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Precipitation radar as a source of hydrometeorological data Bonser, J. D. 1982

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PRECIPITATION RADAR AS A SOURCE OF HYDROMETEOROLOGICAL DATA by J.D. BONSER B . A . S c , U n i v e r s i t y of B r i t i s h C o l u m b i a , 1980 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES De p a r t m e n t Of C i v i l E n g i n e e r i n g We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA A u g u s t 1982 © J.D. B o n s e r , 1982 In presenting t h i s thesis in p a r t i a l fulfilment of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t freely available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by his or her representatives. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of C i v i l Engineering The University of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date: 20 August 1982 i i ABSTRACT The a p p l i c a t i o n of r a d a r - d e r i v e d p r e c i p i t a t i o n measurements t o e n g i n e e r i n g h y d r o l o g y i s i n v e s t i g a t e d i n t h i s t h e s i s . The n a t u r e of p r e c i p i t a t i o n phenomena and c u r r e n t measurement t e c h n i q u e s a r e i n t r o d u c e d , f o l l o w e d by a d e t a i l e d e x p l a n a t i o n o f r a d a r a s a q u a n t i t a t i v e measurement t o o l . A r c h i v e d a t a f o r t h e o p e r a t i o n a l SCEPTRE r a d a r i n A b b o t s f o r d f o r f i v e s t o r m e v e n t s was o b t a i n e d from t h e C a n a d i a n A t m o s p h e r i c E n v i r o n m e n t S e r v i c e . E r r o r s i n h e r e n t i n t h i s d a t a and t h o s e i n t r o d u c e d d u r i n g p r o c e s s i n g a r e i n v e s t i g a t e d , and a c o m p a r i s o n w i t h p o i n t r a i n g a u g e v a l u e s i s g i v e n . An i n t e r a c t i v e c o l o u r image d i s p l a y s y s t e m i s p r e s e n t e d and p r e c i p i t a t i o n p a t t e r n s seen i n t h e d i s p l a y e d image s e q u e n c e s a r e d i s c u s s e d . A p p l i c a t i o n s of r a d a r - d e i r i v e d r a i n f a l l d a t a t o e n g i n e e r i n g r u n o f f models a r e d e s c r i b e d , and t h e b e n e f i t s and l i m i t a t i o n s of t h i s d a t a s o u r c e a r e s t u d i e d . An u r b a n r u n o f f c a s e s t u d y u s i n g t h e Storm Water Management Model t o s i m u l a t e a c a t c h m e n t i n V a n c o u v e r i s g i v e n , and c o n c l u s i o n s r e g a r d i n g t h e s p a t i a l and t e m p o r a l r e s o l u t i o n r e q u i r e m e n t s of r a i n f a l l d a t a s o u r c e s a r e drawn from t h e r e s u l t s . The t h e s i s c o n c l u d e s w i t h recommendations f o r improvements t o t h e SCEPTRE r a d a r and t o t h e a r c h i v e s y s t e m t o make r a d a r d a t a more u s e f u l t o e n g i n e e r i n g h y d r o l o g i s t s . i i i TABLE OF CONTENTS ABSTRACT i i TABLE OF CONTENTS i i i 'LIST OF TABLES v LIST OF FIGURES v i ACKNOWLEDGEMENT i x 1 INTRODUCTION 1 2 PRECIPITATION 3 2.1 I n t r o d u c t i o n 3 2.2 The S t r u c t u r e Of P r e c i p i t a t i o n Systems 3 2.3 The Measurement Of P r e c i p i t a t i o n 5 2.4 H y d r o l o g i c I m p l i c a t i o n s 6 3 RADAR MEASUREMENT OF PRECIPITATION 8 3.1 I n t r o d u c t i o n 8 3.2 P r i n c i p l e s Of Radar 8 3.3 The Radar E q u a t i o n 11 3.4 The Z-R R e l a t i o n 15 3.5 L i m i t a t i o n s To Radar Measurement Of P r e c i p i t a t i o n 17 3.6 D i g i t a l T e c h n i q u e s For Q u a n t i t a t i v e R a i n f a l l Measurement 25 3.7 The SCEPTRE Radar 27 4 RADAR-DERIVED PRECIPITATION MEASUREMENTS OVER THE VANCOUVER AREA 39 4.1 I n t r o d u c t i o n 39 4.2 The A b b o t s f o r d SCEPTRE Radar I n s t a l l a t i o n 39 4.3 Data O b t a i n e d From The AES A r c h i v e 40 4.4 E r r o r s In CAPPI Data 44 4.5 Comparison W i t h R a i n Guage Records 51 4.6 I n t e r a c t i v e Image D i s p l a y System 62 4.7 P a t t e r n s Of P r e c i p i t a t i o n Over The Vancouver Area 74 5 HYDROLOGICAL APPLICATIONS OF SCEPTRE RADAR DATA 85 5.1 I n t r o d u c t i o n 85 5.2 G e n e r a l A p p l i c a t i o n s 85 5.3 A p p l i c a t i o n To E n g i n e e r i n g H y d r o l o g y - Runoff M o d e l l i n g 90 5.4 E n g i n e e r i n g Use Of R a d a r - D e r i v e d P r e c i p i t a t i o n D a t a : Urban Runoff Case Study 93 5.5 Recommendations For Improvements To The SCEPTRE Radar And Data A r c h i v e And R e t r i e v a l 101 6 CONCLUSIONS 105 REFERENCES AND BIBLIOGRAPHY 107 APPENDIX A - SCEPTRE Radar Measurement A l t i t u d e s C o r r e c t e d f o r E a r t h C u r v a t u r e and S t a n d a r d Beam R e f r a c t i o n 113 APPENDIX B - Summary of AES D a i l y Raingauge L o c a t i o n s and Gauge/Radar Measurements 118 APPENDIX C - F l o w c h a r t Showing CAPPI Image G r i d E x t r a c t i o n , E r r o r C o r r e c t i o n , Data T r a n s f e r , and Image G e n e r a t i o n P r o c e s s e s 121 V LIST OF TABLES 3.1 Frequencies used i n weather radar systems 16 3.2 Raytheon WSR-807 radar s p e c i f i c a t i o n s 29 3.3 SCEPTRE C scan range and s e n s i t i v i t y options 35 3.4 Normal CAPPI c o n s t r u c t i o n t a b l e : range gate s e t t i n g s and corresponding e l e v a t i o n angles 36 4.1 Storm records received from AES 42 4.2 2 km CAPPI c o n s t r u c t i o n t a b l e 43 4.3 SCEPTRE DVIP s i g n a l - r a i n f a l l i n t e n s i t y c a l i b r a t i o n ..43 4.4 G/R r a t i o s f o r 5 days of r a i n f a l l data 59 LIST OF FIGURES 3.1 Radar d e t e c t i o n of p r e c i p i t a t i o n 9 3.2 T y p i c a l antenna beam pa t t e r n 10 3 .5 Beam volume 13 3.4 E f f e c t of the curvature of the earth 18 3.5 At t e n u a t i o n of the radar beam by i n t e r v e n i n g p r e c i p i t a t i o n 18 3.6 L i m i t a t i o n of r e s o l u t i o n due to pulse length 21 3.7 L i m i t a t i o n of r e s o l u t i o n due t o beam width 21 3.8 O c c u l t a t i o n of the radar beam ...22 3.9 Cone of s i l e n c e 23 3.10 S u p e r r e f r a c t i o n of the radar beam 24 3.11 CAPPI Cons t r u c t i o n 26 3.12 AES weather radar i n s t a l l a t i o n s i n Canada 27 3.13 SCEPTRE radar schematic 28 3.14 Radar tower and c o n t r o l b u i l d i n g at the Abbotsford SCEPTRE s i t e 30 3.15 Tran s m i t t e r , r e c e i v e r , and antenna c o n t r o l equipment .31 3.16 3.66 m diameter p a r a b o l i c antenna and pedastal mount .32 3.17 PPI i n d i c a t o r and c o n t r o l console 33 3.18 PDP-11/35 minicomputer and system c o n t r o l equipment ..34 3.19 O s c i l l o s c o p e showing a s i n g l e A scan and the PPI d i s p l a y 35 3.20 Processing c y c l e t i m i n g c h a r t 36 3.21 An example of a CAPPI f a c s i m i l e from the Abbotsford SCEPTRE i n s t a l l a t i o n 37 4.1 L o c a t i o n of the Abbotsford SCEPTRE radar w i t h cone of s i l e n c e and 20 km range r i n g s marked 40 4.2 Coverage of 2 km CAPPI 41 4.3 Uncorrected cumulative r a i n f a l l p a t t e r n f o r the December 1980 storm 45 4.4 Convolution pattern f o r image c o r r e c t i o n 47 4.5 Corrected cumulative r a i n f a l l p a t t e r n f o r the December 1980 storm 48 4.6 Comparison of c o r r e c t e d and uncorrected cumulative p r o f i l e s f o r December 1980 storm 49 4.7 Locations of s t a t i o n a r y echoes 50 4.8 Lo c a t i o n of AES raingauge s t a t i o n s with d a i l y records .52 4.9 Radar/raingauge r e g r e s s i o n r e l a t i o n s h i p f o r 20 December 1980 53 4.10 Radar/raingauge re g r e s s i o n r e l a t i o n s h i p f o r 21 December 1980 54 4.11 Radar/raingauge re g r e s s i o n r e l a t i o n s h i p f o r 12 February 1981 55 4.12 Radar/raingauge re g r e s s i o n r e l a t i o n s h i p f o r 13 February 1981 56 4.13 Radar/raingauge re g r e s s i o n r e l a t i o n s h i p f o r 14 February 1981 57 4.14 Hyetal surface r e p r e s e n t a t i o n s of radar and raingauge data f o r 20 December 1980 58 4.15 G/R r a t i o as a f u n c t i o n of distance from the radar ...60 4.16 Character matrix r e p r e s e n t a t i o n of the r a i n f a l l p a t t e r n s 64 4.17 I s o h y e t a l r e p r e s e n t a t i o n of the r a i n f a l l p a t terns ....65 4 . 1 8 H y e t a l surface r e p r e s e n t a t i o n of the r a i n f a l l p a t t e r n s 67 4.19 Colour r e p r e s e n t a t i o n of the r a i n f a l l p a t t e r n s 68 4.20 IBM Personal Computer used f o r d i s p l a y i n g the CAPPI images 71 4.21 MTS host - IBM PC data t r a n s f e r l i n k 72 4.22 Colour monitor d i s p l a y showing range r i n g s and overl a y map 73 4.23 R a i n f a l l i n t e n s i t y p a t t e r n - 1044 GMT 22 December 1980 75 v i i i 4.24 R a i n f a l l i n t e n s i t y p a t t e r n - 1054 GMT 22 December 1980 75 4.25 R a i n f a l l i n t e n s i t y p a t t e r n - 1104 GMT 22 December 1980 76 4.26 R a i n f a l l i n t e n s i t y p a t t e r n - 1114 GMT 22 December , 1980 76 4.27 R a i n f a l l i n t e n s i t y p a t t e r n - 1124 GMT 22 December 1980 77 4.28 R a i n f a l l i n t e n s i t y p a t t e r n - 1134 GMT 22 December 1980 77 4.29 R a i n f a l l i n t e n s i t y p a t t e r n - 1144 GMT 22 December 1980 78 4.30 R a i n f a l l i n t e n s i t y p a t t e r n - 1154 GMT 22 December 1980 78 4.31 R a i n f a l l i n t e n s i t y p a t t e r n - 1204 GMT 22 December 1980 79 4.32 R a i n f a l l i n t e n s i t y p a t t e r n - 1214 GMT 22 December 1980 v 79 4.33 R a i n f a l l i n t e n s i t y p a t t e r n - 1224 GMT 22 December 1980 80 4.34 R a i n f a l l i n t e n s i t y p a t t e r n - 1234 GMT 22 December 1980 80 4.35 R a i n f a l l i n t e n s i t y p a t t e r n - 1244 GMT 22 December 1980 81 4.36 R a i n f a l l i n t e n s i t y p a t t e r n - 1254 GMT 22 December 1980 81 4.37 R a i n f a l l i n t e n s i t y p a t t e r n - 1304 GMT 22 December 1980 82 5.1 Map of Fraserview catchment 95 5.2 SWMM o u t l e t hydrograph f o r the Fraserview catchment, December 1980 storm 96 5.3 Comparison of SWMM o u t l e t hydrographs f o r normal and reversed storm d i r e c t i o n s 97 5.4 Comparison of SWMM hydrographs from ten minute radar and equivalent hourly gauge data 98 5.5 S p a t i a l / t e m p o r a l r e s o l u t i o n requirements of r a i n f a l l data - storm v e l o c i t y 60 kmh 100 i x ACKNOWLEDGEMENTS' I would l i k e to take t h i s opportunity to express my a p p r e c i a t i o n and thanks t o my adv i s o r Dr. B i l l Caselton f o r h i s advice and guidance during the research and the pre p a r a t i o n of t h i s t h e s i s , and to Dr. Denis R u s s e l l f o r h i s val u a b l e suggestions and review of t h i s work. Richard Brun of the UBC C i v i l Engineering Department, Ken Anderson of the M i n i s t r y of Transport, and Rowan B i r c h and Wayne Reese of the C i t y of Vancouver a l s o deserve thanks f o r a l l t h e i r e f f o r t s on my beh a l f . In a d d i t i o n , I would l i k e to commend the UBC Computing Centre f o r the e x c e l l e n t s e r v i c e i t has provided during the course of my research. The f i n a n c i a l a s s i s t a n c e of the N a t i o n a l Research C o u n c i l of Canada i n the form of a s c h o l a r s h i p and research funding i s g r a t e f u l l y acknowledged. F i n a l l y , I would l i k e to express my si n c e r e a p p r e c i a t i o n to many f r i e n d s whose support, encouragement, and kindness throughout the l a s t two years have made my graduate s t u d i e s a pleasant and memorable experience. 1 CHAPTER I INTRODUCTION Water resources management involves the planning, design, • construction, and operation of water control f a c i l i t i e s . In every phase of t h i s management process, decisions are required which demand that the engineer use his knowledge and i n t u i t i v e judgement to achieve close to optimal r e s u l t s . The increasing complexity of water resource systems achieving t h i s high l e v e l of performance has necessitated more complex analysis procedures, which in turn have required greater quantities of r e l i a b l e data. The analysis and design of water resources projects i s i d e a l l y based on long records of hydrometric data. However, in many instances t h i s information i s not a v a i l a b l e , and a l t e r n a t i v e methods must be used. One approach i s to model the runoff and streamflow process and thereby use p r e c i p i t a t i o n records in l i e u of the flow data. This hydrometeorological approach demands accurate p r e c i p i t a t i o n data with s u f f i c i e n t s p a t i a l and temporal resolution to allow r e a l i s t i c modelling practices. The recent a v a i l a b i l i t y of a t r u l y operational p r e c i p i t a t i o n measurement system and data archive o f f e r i n g much higher temporal and s p a t i a l resolution than conventional raingauge networks would, at f i r s t glance, be expected to o f f e r s i g n i f i c a n t and r e l a t i v e l y easy to achieve benefits in 2 many areas of water resources a n a l y s i s . However, at c l o s e r i n v e s t i g a t i o n these advantages are accompanied by sources of e r r o r and problems of r e s o l u t i o n which only become apparent when the high r e s o l u t i o n data i s s c r u t i n i z e d . A d d i t i o n a l problems of d e a l i n g with the l a r g e q u a n t i t i e s of information generated are a l s o r a i s e d . The o r i g i n a l i n t e n t was to focus on the adaptation and a p p l i c a t i o n of the new data source i n conjunction with s p a t i a l l y and temporally s e n s i t i v e water resources models. While t h i s o b j e c t i v e was reached to a degree, the r a d i c a l l y d i f f e r e n t nature of the radar system of measurement n e c e s s i t a t e d f a r greater e f f o r t overcoming the data d e f e c t s and researching ways to access and view the data. The r e s u l t i n g explanation of the radar measurement process and data p r e s e n t a t i o n i n the research arose, not from l o s i n g s i g h t of the p o t e n t i a l data a p p l i c a t i o n s , but by the n e c e s s i t y of addressing a l l data r e l a t e d problems to promote a r e a l i s t i c foundation f o r i t s subsequent e x p l o i t a t i o n . 3 CHAPTER II PRECIPITATION 2.1 I n t r o d u c t i o n P r e c i p i t a t i o n data i s one of the key i n g r e d i e n t s i n any s i m u l a t i o n of urban r u n o f f . Although most of the physics of p r e c i p i t a t i o n mechanisms are understood, from an engineering design viewpoint p r e c i p i t a t i o n inputs to water resources systems are s t i l l not s a t i s f a c t o r a l l y d e f i n e d . Because p r e c i p i t a t i o n i s h i g h l y v a r i a b l e i n both space and time, accurate p o i n t measurement i s d i f f i c u l t t o achieve and e s t i m a t i o n of p r e c i p i t a t i o n depth accumulated over an area i s subject to l a r g e e r r o r . In t h i s chapter the nature of p r e c i p i t a t i o n i s s t u d i e d , and c u r r e n t techniques f o r measurement, i n c l u d i n g raingauge networks, radar systems, and remote sensing by s a t e l l i t e , are reviewed. 2.2 The S t r u c t u r e of P r e c i p i t a t i o n Systems P r e c i p i t a t i o n i s a f a m i l i a r n a t u r a l phenomenon. Although most people have some awareness of the v a r i a b i l i t y of r a i n f a l l i n both space and time, they would have great d i f f i c u l t y i n q u a n t i f y i n g t h e i r i n t u i t i v e impression of t h i s v a r i a b i l i t y . M e t e o r o l o g i s t s have adopted a q u a l i t a t i v e c l a s s i f i c a t i o n scheme and view p r e c i p i t a t i o n phenomena at three s c a l e s : 1 . Synoptic or macroscale. Storms which are d i s c e r n a b l e on 4 weather s a t e l l i t e photographs, a s s o c i a t e d with low pressure and f r o n t a l systems, are synoptic s c a l e events. They are g e n e r a l l y on the order of hundreds of kilometres i n s i z e . In the Vancouver area they are u s u a l l y i n the form of c y c l o n i c systems moving eastward o f f the P a c i f i c Ocean. 2. Mesoscale. Within the band of p r e c i p i t a t i o n from the synoptic system i s a "pebbly s t r u c t u r e " of patterns of p r e c i p i t a t i o n . These areas are t y p i c a l l y ten to f i f t y km i n extent and s i x t y km apart, and move i n step as the band of p r e c i p i t a t i o n sweeps over the e a r t h . Thuderstorms are another example of mesoscale systems. 3 . Convective or m i c r o s c a l e . Within mesoscale events are convective c e l l s . These c e l l s , which are res p o n s i b l e f o r intense bursts of r a i n f a l l over short time i n t e r v a l s , range from two to s e v e r a l kilometres a c r o s s , and l a s t f o r up to an hour. The are generated by a l o c a l i n s t a b i l i t y i n the atmosphere, grow r a p i d l y , and often contain strong updrafts and downdrafts. P r e c i p i t a t i o n i s oft e n c l a s s i f i e d i n t o three p r i n c i p a l c a t e g o r i e s : c y c l o n i c , orographic, and co n v e c t i v e , depending on the dominant l i f t mechanism causing the p r e c i p i t a t i o n . C y c l o n i c r a i n f a l l a r i s e s when moist airmasses i n a f r o n t a l system r i s e due to the h o r i z o n t a l convergence of envelopes of a i r having d i f f e r e n t temperatures. In orographic p r e c i p i t a t i o n , u p l i f t due to the passage of the airmass over a topographic feature causes the p r e c i p i t a t i o n . Convective 5 r a i n f a l l occurs when d i f f e r e n t i a l heating of adjacent airmasses generates a l o c a l i n s t a b i l i t y . In the Vancouver area, e x t r a - t r o p i c a l c y c l o n i c systems are the p r i n c i p a l source of p r e c i p i t a t i o n , w i t h orographic e f f e c t s superimposed to y i e l d l o c a l v a r i a t i o n s i n the amount of r a i n f a l l received [Hay 73]. 2.3 The Measurement of P r e c i p i t a t i o n The s u c c e s s f u l design and operation of water resources p r o j e c t s depends on the c o l l e c t i o n and accurate i n t e r p r e t a t i o n of basic hydrometeorological data. P r e c i p i t a t i o n measurements play an important r o l e i n many water resources analyses, yet the amount and q u a l i t y of the data provided are often inadequate f o r engineering purposes. The e a r l i e s t , and s t i l l most common, source of r a i n f a l l data are p o i n t raingauges. Although these gauges take many forms, ranging from simple v e r t i c a l c y l i n d r i c a l r e s e r v o i r s manually read on a d a i l y b a s i s t o s o p h i s t i c a t e d automatic re c o r d i n g devices t a k i n g measurements every few minutes, they a l l provide only point measurements. A r e a l v a r i a t i o n s and accumulations must be i n t e r p o l a t e d from a network of such instruments and are t h e r e f o r e subject to e r r o r . Since the 1940's an a l t e r n a t i v e method of sensing p r e c i p i t a t i o n has been e v o l v i n g using radar. Radar measurement of r a i n f a l l i s accomplished by the i n t e r p r e t a t i o n of r a d i o wave echoes from regions of hydrometeors i n the 6 atmosphere. I t provides information on the s p a t i a l d i s t r i b u t i o n of the p r e c i p i t a t i o n with a temporal r e s o l u t i o n comparable to or b e t t e r than that of a recording gauge, but, because i t remotely senses the p r e c i p i t a t i o n , i t i s more prone t o ^ e r r o r than d i r e c t gauge readings. A more r e c e n t l y developed p o t e n t i a l source of r a i n f a l l data i s s a t e l l i t e imagery. S a t e l l i t e s provide wide-range coverage of the e a r t h and are an i n v a l u a b l e source of information f o r macroscale systems. However, r e s o l u t i o n c o n s t r a i n t s make measurements over small basins i m p r a c t i c a l and hence s a t e l l i t e data does not appear to o f f e r an a l t e r n a t i v e to radar data i n small basins and urban runoff s t u d i e s . 2.4 Hydrologic I m p l i c a t i o n s In the context of small b a s i n s , i t i s the microscale p r e c i p i t a t i o n source which i s mostly r e s p o n s i b l e for the peak runoff response. As the area of the basin increases i t s c r i t i c a l runoff response becomes more dependent upon the character of the mesoscale and e v e n t u a l l y the macroscale events. While t h i s i s suggested by experience, there i s , as y e t , no way of s p e c i f y i n g what temporal and s p a t i a l r e s o l u t i o n s are adequate f o r any p a r t i c u l a r basin or r e g i o n . Because of the cost and d i f f i c u l t i e s i n v o l v e d , very l i t t l e experience has been gained w i t h p r e c i p i t a t i o n data bases having s p a t i a l and temporal r e s o l u t i o n s which approach or 7 exceed minimal requirements. Radar measurement of p r e c i p i t a t i o n now o f f e r s the promise of p r o v i d i n g much higher r e s o l u t i o n p r e c i p i t a t i o n data bases than have been a v a i l a b l e i n the p a s t . This form of measurement i s des c r i b e d i n d e t a i l i n ' t h e f o l l o w i n g chapter. 8 CHAPTER I I I RADAR MEASUREMENT OF PRECIPITATION 3.1 I n t r o d u c t i o n In t h i s chapter both the t h e o r e t i c a l and p r a c t i c a l aspects of the measurement of r a i n f a l l by conventional ground-based radar systems are considered. A f t e r o u t l i n i n g the basic p r i n c i p l e s of radar, the radar equation used i n p r e c i p i t a t i o n s t u d i e s i s developed, followed by a d i s c u s s i o n of some of the l i m i t a t i o n s to the use of radar as a measurement t o o l . The chapter concludes with an examination of an e x i s t i n g o p e r a t i o n a l radar system, the Canadian Atmospheric Environment S e r v i c e s SCEPTRE radar, from which the r a i n f a l l data used i n t h i s research was obtained. 3.2 P r i n c i p l e s of Radar Radar has been defined as a "system f o r a s c e r t a i n i n g the d i r e c t i o n and range of obj e c t s from the electromagnetic waves which they r e f l e c t " [ O x f o 5 l ] . In the context of p r e c i p i t a t i o n measurement by radar, the ob j e c t s are hydrometeors such as r a i n d r o p l e t s , i c e p a r t i c l e s , and snowflakes which cause s c a t t e r i n g or r e f l e c t i o n of r a d i o waves. The d e t e c t i o n and subsequent a n a l y s i s of the r e f l e c t e d energy patterns y i e l d s i n f o r m a t i o n on the c h a r a c t e r i s t i c s of the p r e c i p i t a t i o n . In a t y p i c a l radar system, a s i n g l e antenna serves as 9 both the t r a n s m i t t e r and r e c e i v e r of the radio energy. The d i s t a n c e t o the t a r g e t i s determined from the time elapsed between transmission and rec e p t i o n of the waveform, while the p r e c i p i t a t i o n i n t e n s i t y i s r e l a t e d t o the streng t h of the returned s i g n a l ( f i g . 3.1). The t r a n s m i t t e d energy i s sent Figure 3.1 - Radar-detection of p r e c i p i t a t i o n i n short pulses (about one microsecond d u r a t i o n ) , separated by r e l a t i v e l y long s i l e n t periods during which the r e f l e c t e d s i g n a l s are re c e i v e d . The pulse r e p e t i t i o n frequency i s g e n e r a l l y about 300 to 400 per second [Sauv8l]. This f a c t o r determines the maximum u s e f u l range of the radar, which may be no greater than the distance t r a v e l l e d by a r a d i o wave i n h a l f the i n t e r v a l between pu l s e s . I f the per i o d between pulses i s too s h o r t , the echo from a d i s t a n t t a r g e t w i l l have i n s u f f i c i e n t time to retu r n to the r e c e i v e r before the next pulse i s t r a n s m i t t e d , producing image wraparound. A high r e p e t i t i o n frequency enhances the q u a l i t y of the image because a l a r g e r number of pulses are returned from each t a r g e t , but 10 f o r a given system power the energy output of each pulse w i l l be lower. The upper range l i m i t f o r a radar with a pulse r e p e t i t i o n frequency of 300 i s about 500 km, with a co n s i d e r a b l y shorter p r a c t i c a l range. In order to maximize the p r e c i s i o n of the measurement, the t r a n s m i t t e d beam-width i s made as narrow as p o s s i b l e . The t r a n s m i t t e d beam p a t t e r n i s a f u n c t i o n of the s i z e and shape of the antenna and the wavelength of the radar. By using a c i r c u l a r p a r a b o l i c antenna, a symmetric beam p a t t e r n with a h a l f power width of about one degree may be acheived ( f i g . 3.2) [Sau v 8 l ] . Figure 3.2 - T y p i c a l antenna beam p a t t e r n To obt a i n a complete three-dimensional survey of the p r e c i p i t a t i o n system, the radar must scan through m u l t i p l e 11 e l e v a t i o n angles as w e l l as r o t a t e through 360 degrees of azimuth. The returned radar echoes are i n t e g r a t e d to form a comprehensive p i c t u r e of the p r e c i p i t a t i o n . The antenna r o t a t e s at about s i x r e v o l u t i o n s per minute, and i s stepped through the e l e v a t i o n angles under computer c o n t r o l . A complete c y c l e takes about f i v e minutes, the a c t u a l time depending on the number of e l e v a t i o n angles scanned. 3.3 The Radar Equation In order to q u a n t i t a t i v e l y determine the p r e c i p i t a t i o n observed by the radar, a r e l a t i o n s h i p between returned s i g n a l power and p r e c i p i t a t i o n i n t e n s i t y i s r e q u i r e d . Probert-Jones [Prob62] and Battan [Batt59] develop such an equation. Battan gives the power received by a radar antenna f o r s c a t t e r i n g from a s i n g l e target as p . f t A p ° i 1 ( 3 - ° where P t i s the t r a n s m i t t e d power, A p i s the a p e r t u r a l area of a p a r a b o l o i d a l antenna, A i s the wavelength of the r a d i a t i o n , r i s the distance to t a r g e t , and i s the b a c k - s c a t t e r i n g c r o s s - s e c t i o n , which i s defined as "the area i n t e r c e p t i n g that amount of power which, i f s c a t t e r e d i s o t r o p i c a l l y , would r e t u r n to the r e c e i v e r an amount of power equal to that a c t u a l l y r e c e i v e d . " The e f f e c t i v e aperture i s a f u n c t i o n of A and the gain of the antenna, G, which i s defined as "the r a t i o of the power r a d i a t e d by an i s o t r o p i c antenna necessary to 12 produce a given f i e l d s t r e n g t h at a given d i s t a n c e t o the power r a d i a t e d by a d i r e c t i o n a l antenna producing the same f i e l d s t r e n g t h at the same di s t a n c e i n the d i r e c t i o n of maximum tr a n s m i s s i o n " [Prob62], ' In the case of hydrometeors, a lar g e group of t a r g e t s i n t e r c e p t the radar beam at any one time, and thus the returned s i g n a l i s an i n t e g r a t i o n of i n d i v i d u a l s i g n a l s from each of the p a r t i c l e s w i t h i n the volume i l l u m i n a t e d . When the received power i s averaged over a lar g e number of random arr a y s of p a r t i c l e s , equation 3.1 becomes n I l - o (3.2) w i t h the summation over a volume V from which the back-s c a t t e r e d s i g n a l i s r e c e i v e d . This volume i s given approximately by V - *(rl)(r±) \ 2 2 2 (3.3) where 6 and • are the h o r i z o n t a l and v e r t i c a l beam widths r e s p e c t i v e l y , and -| i s the length of the t r a n s m i t t e d pulse ( f i g . 3.3). Thus the radar equation may be r e w r i t t e n as 72X 2r 2 (3 .4) The s c a t t e r i n g of r a d i o energy by a s i n g l e s p h e r i c a l 13 p u l i t I t n g t h ^ Figure 3.3 - Beam v o l ume azimuth beomwidth 6 • livation btamwidth dS d r o p l e t i s given by the Rayl e i g h approximation [Batt59] '1 - 64 |K|2 A 6 A* (3.5) where A i s the wavelength of the r a d i a t i o n , K i s the complex index of r e f r a c t i o n which i s a f u n c t i o n of the r e f r a c t i v e index of the transmis s i o n medium and the absorption c o e f f i c i e n t of the targe t m a t e r i a l , and a ± i s the droplet r a d i u s . The average returned power from a region of hydrometeors may now be c a l c u l a t e d by s u b s t i t u t i n g i n equation 3.4 to y i e l d p . 8*5 p t A p e * h r — r — , K 1 r 2 V (3.6) Probert-Jones [Prob62] completes a s i m i l a r d e r i v a t i o n using a more accurate but complex estimate of the i l l u m i n a t e d volume to y i e l d 14 l o g e 2 P t A | 6 * h i V (3.7) where A e i s the e f f e c t i v e a e r i a l aperture, which i s A p adjusted f o r lo s s e s i n the waveguide and radome. S p e c i f y i n g the s i z e of the p a r t i c l e s by t h e i r diameters and using the symbol Z, the r e f l e c t i v i t y f a c t o r i n d e c i b e l s , to represent 10 l o g 1 0 ). a ± * equation 3.7 becomes V P r - —1 _L_£ ± J _ Z (3.8) 64 l o g „ 2 \ A 6 / r 2 This equation may be broken down i n t o f i v e segments. The f i r s t term i s a constant. The terms w i t h i n the parentheses are c h a r a c t e r i s t i c s of the radar and are a l s o constant f o r a given system. For d r o p l e t s of water i n the atmosphere, the |K.|2 term i s approximately equal to 0.93, and f o r i c e p a r t i c l e s i s about 0.19, but 0.93 i s g e n e r a l l y used since the t a r g e t i s assumed to be water [Sa u v 8 l ] . Thus the d e t e c t i o n of p r e c i p i t a t i o n i s p r i m a r i l y a f u n c t i o n of the s i z e of the hydrometeors and t h e i r d i s t a n c e from the radar. The decrease i n returned s i g n a l power with i n c r e a s i n g d i s t a n c e i s accomodated i n the r 2 term, with n o r m a l i z a t i o n of the range accomplished by " s e n s i t i v i t y time c o n t r o l . " The d e r i v a t i o n of t h i s equation i s based on a number of assumptions, the most important of which are: 15 1. the radar r e f l e c t i v i t y i s uniform over the i l l u m i n a t e d volume; 2. the Rayleigh approximation i s v a l i d ( d r o p l e t s i z e i s small r e l a t i v e to the wavelength); 3. the i l l u m i n a t e d volume i s completely f i l l e d w ith hydrometeors; 4. a l l echoes come from the same type of hydrometeor ( r a i n , snow, e t c . ) ; 5. the beam i n t e n s i t y cross s e c t i o n can be approximated by a normal curve; 6. the amount of m u l t i p l e s c a t t e r i n g i s n e g l i g i b l e ; 7. the i n c i d e n t and back-scattered r a d i a t i o n are l i n e a r l y p o l a r i z e d [Croz75]. Under o p e r a t i o n a l c o n d i t i o n s , Z i s g e n e r a l l y accurate to w i t h i n a f a c t o r of about 1.5, on the order of the measurement p r e c i s i o n of the radar [Sauv8l]. 3.4 The Z-R R e l a t i o n P r e c i p i t a t i o n i n t e n s i t y (R) must be r e l a t e d to the radar r e f l e c t i v i t y f a c t o r (Z) before measurements of r a i n f a l l can be made. Since the d i s t r i b u t i o n of drop s i z e s i s not g e n e r a l l y known and v a r i e s i n time and space, and since v e r t i c a l a i r c u r r e n t s o f t e n e x i s t which e f f e c t the rate at which d r o p l e t s reach the ground i n the form of p r e c i p i t a t i o n , an exact t h e o r e c t i c a l Z-R r e l a t i o n i s not p o s s i b l e . A number of d i f f e r e n t researchers have e s t a b l i s h e d e m p i r i c a l r e l a t i o n s h i p s between Z and R f o r v a r i o u s r a i n and snow c o n d i t i o n s [Mars48], 16 [Wexl48], [Best50], [Jone55], [Gunn58], a l l of which take the form Z - aR b (3.9) where a and b are constants. The Marshall-Palmer r e l a t i o n i s the most widely used f o r the measurement of r a i n , f o r which the c o e f f i c i e n t s a and b have the values 200 and 1.6 r e s p e c t i v e l y [ W i l s 7 9 ] , [ S a u v 8 l ] . The minimum dro p l e t s i z e detectable by a radar i s q u i t e s e n s i t i v e to the wavelength of the r a d i a t i o n chosen (equation 3.8). For met e o r o l o g i c a l work, wavelengths i n the range one to twenty cm are g e n e r a l l y used ( t a b l e 3.1). Shorter Band Wavelength Range Frequency Uses K 0.75 - 2.4 cm 25 GHz cloud physics research X 2.4 - 3.75 cm 10 GHz weather surveillance (on board a i r c r a f t ) C 3.75 - 7.5 cm 6 GHz p r e c i p i t a t i o n measurement S 7.5 - 15 cm 3 GHz p r e c i p i t a t i o n measurement, terminal a i r - t r a f f i c control L 15 - 30 cm 1 .3 GHz route a i r - t r a f f i c control Table 3.1 - Frequencies used i n weather radar systems wavelengths are appropriate f o r cloud physics s t u d i e s , since smaller d r o p l e t s may be detected, while f i v e to ten cm radars are p r e f e r r e d f o r p r e c i p i t a t i o n measurement because they are l e s s s u s c e p t i b l e to a t t e n u a t i o n . Because ten cm systems r e q u i r e much more powerful t r a n s m i t t e r s and l a r g e r antennas, 17 f i v e cm radars are most common i n Canadian o p e r a t i o n a l p r a c t i c e [ S a u v 8 l ] . 3.5 L i m i t a t i o n s to Radar Measurement of P r e c i p i t a t i o n Each radar system must be c a l i b r a t e d before i t becomes a u s e f u l measurement t o o l . Based on the c o r r e l a t i o n of values computed using equation 3.7 and measured re c e i v e d power, Probert-Jones [Prob62] showed that on average the measured values were s l i g h t l y l e s s than 1.5 dB lower than those p r e d i c t e d by the theory. Even f o l l o w i n g c a r e f u l c a l i b r a t i o n , there remain p o t e n t i a l l y s e r i o u s sources of e r r o r i n the measurements and l i m i t a t i o n s to the d e t e c t i o n c a p a b i l i t y of the radar. The t h e o r e t i c a l maximum range d e f i n e d by the pulse r e p e t i t i o n frequency may be superceded by another c o n s t r a i n t : the e f f e c t of the curvature of the ea r t h ( f i g . 3.4). At a dist a n c e of about 400 km from the radar the beam, even at i t s minimum e l e v a t i o n angle, w i l l pass over the top of most p r e c i p i t a t i o n systems [ W i l l 7 3 ] . The output power of the radar may a l s o be a l i m i t i n g f a c t o r . The minimum t h r e s h o l d of s i g n a l d e t e c t i o n may determine the e f f e c t i v e maximum range of a low power system. A t t e n u a t i o n of the radar beam by i n t e r v e n i n g p r e c i p i t a t i o n , clouds, and atmospheric gases may be a se r i o u s problem, p a r t i c u l a r l y f o r shorter wavelength radars ( f i g . 3.5). Of these, a t t e n u a t i o n by p r e c i p i t a t i o n i s the most 18 radar biom - radius ef curvature it 1.33 time* thot of the earth Figure 3.4 - E f f e c t of the curvature of the earth Figure 3.5 - Attenuation of the radar beam by i n t e r v e n i n g p r e c i p i t a t i o n important. For a f i v e cm radar, Weible and Sirmans [Weib76] give the a t t e n u a t i o n as A ± - I _ R j 0 ' 9 9 2 0.00374Ar (3.10) where A A i s the a t t e n u a t i o n r a t i o expressed i n dB, Rj i s the tru e r a i n f a l l i n t e n s i t y i n mm/hr f o r the j t h beam segment, and Ar i s the length of the segment i n km. The a t t e n t u a t i o n r a t i o i s 19 A ± - 10 l o g 1 0 - f T (3.11) where R ' i s the attenuated r a i n f a l l r a t e . Using t h i s r e l a t i o n , s equation 3.10 may be r e w r i t t e n i n a more u s e f u l form as R 1 n j - i 10 0 . 00037»» R ,0 # 9 9 2 A r (3.12) For example, the recorded r a i n f a l l r ate on a f i v e cm radar decreases about one mm/hr for every ten km i n which the beam passes through ten mm/hr p r e c i p i t a t i o n . The e f f e c t for higher r a i n f a l l r a t e s i s even more s i g n i f i c a n t , and s e v e r a l authors [Weib76], [ H i t s 5 4 ] , [ A t l a 5 l ] recommend against using a f i v e cm radar f o r q u a n t i t a t i v e measurement of severe storms. In a d d i t i o n , the minimum d e t e c t a b l e r a i n f a l l r ate increases with d i s t a n c e from the radar. Thus, to obtai n c o n s i s t e n t measurements which are s p a t i a l l y independent, the minimum s i g n a l t h r e s h o l d f o r the e n t i r e area scanned by the radar must be set to a l e v e l corresponding to the minimum detectable p r e c i p i t a t i o n rate at the maximum range. The b u i l d u p of a p r e c i p i t a t i o n f i l m on the surface of the radome a l s o attenuates the re c e i v e d s i g n a l , and since the th i c k n e s s of the f i l m v a r i e s w i t h the angle and surface c h a r a c t e r i s t i c s of the radome s h e l l , the amount of at t e n u a t i o n i s a f u n c t i o n of the e l e v a t i o n angle and d i r e c t i o n of the beam. Kodaira [Koda80] p r e d i c t s an increase i n a t t e n u a t i o n of 20 over three dB f o r f i v e mm/hr or more p r e c i p i t a t i o n at the s i t e of a f i v e cm radar, while Wilson [Wils78] contends that t h i s value should be only one dB f o r up to f o r t y mm/hr r a i n f a l l . Wilson and Brandes [Wils79] summarize some of the mi c r o p h y s i c a l and kinematic e f f e c t s on the Z-R r e l a t i o n s h i p , and hence on the accuracy of radar r a i n f a l l measurements. Evaporation, c o l l i s i o n and coalescence of d r o p l e t s , s i z e s o r t i n g i n regions of strong i n f l o w and outflow, and v e r t i c a l u p drafts are given as causes of overestimation of p r e c i p i t a t i o n . S i m i l a r l y , a c c r e t i o n of cloud p a r t i c l e s , d r o p l e t breakup, and v e r t i c a l downdrafts lead to underestimates. These "processes act i n combination to modify the d r o p - s i z e d i s t r i b u t i o n and produce a complex net r e s u l t . " There are two p r i n c i p l e f a c t o r s which l i m i t the r e s o l u t i o n of the radar. F i r s t l y , s ince each t a r g e t i s i l l u m i n a t e d by the e n t i r e l e n g t h of the emitted p u l s e , an echo i s returned which i s one pulse length longer than the targe t i t s e l f . The r e c e i v e r processor halves the t o t a l d i stance t r a v e l l e d by the pulse to determine the range of the o b j e c t , with the r e s u l t that a l l echoes appear longer by h a l f a pulse l e n g t h . Thus the radar i s incapable of d i s t i n g u i s h i n g d i s t i n c t t a r g e t s which l i e on the same azimuthal l i n e and have a separation of l e s s than ^ ( f i g . 3.6). For a radar set wi t h a two microsecond pulse emission, t h i s d i s t a n c e i s 300 m. The second problem i s due to the increase i n the width of the beam wit h d i s t a n c e from the radar ( f i g . 3.7). For example, a 21 t •2 separa te ce l ls oppeor os a s i n g l e e c h o Figure 3.6 - L i m i t a t i o n of r e s o l u t i o n due to pulse length F i g u r e 3.7 - L i m i t a t i o n of r e s o l u t i o n due to beam width one degree beam has a width of over four km at a range of 240 separ a t i o n of l e s s than one beam width produce a s i n g l e echo r e t u r n , and the p r o b a b i l i t y that the e n t i r e i l l u m i n a t e d volume i s not f i l l e d w ith hydrometeors increases as the beam width grows. The net e f f e c t i s a l o s s of r e s o l u t i o n , leading to an averaging or smoothing of i n t e n s i t i e s at longer ranges. Poor s i t i n g of the radar antenna may lead to problems of ground c l u t t e r and reduced accuracy of measurements made with small beam e l e v a t i o n angles [Smit72]. Obstacles such as b u i l d i n g s and ve g e t a t i o n c l o s e t o the radar s i t e , or more d i s t a n t mountains, may p a r t i a l l y or completely obstruct the beam at c e r t a i n angles ( f i g . 3.8). These objects not only 2 separate c e l l s a p p e a r a s a t i n g l e e c h o km. As a consequence, d i s c r e t e t a r g e t s with an azimuthal 22 Figure 3.8 - O c c u l t a t i o n of the radar beam prevent measurements from being made i n t h e i r shadows, but often appear as anomolous p r e c i p i t a t i o n i n the recorded data. With appropriate processing software the spurious data p o i n t s can be removed, but l i t t l e can be done to r e p a i r the o c c u l t a t i o n "holes" i n the area covered by the radar. There are two f a c t o r s which l i m i t the usefulness of the radar at short ranges. The f i r s t i s the e f f e c t of si d e lobes, which may produce echo d i s t o r t i o n s f o r t a r g e t s w i t h i n ten to twenty km of the radar. Secondly, since the maximum e l e v a t i o n angle of the radar i s u s u a l l y l e s s than f o r t y degrees, there i s a cone-shaped area around the radar (known as the "cone of s i l e n c e " ) i n which no measurements are p o s s i b l e ( f i g . 3.9) [Sa u v 8 l ] . Electromagnetic waves r e f r a c t when they pass through a d e n s i t y change i n the transmission medium. Since the atmosphere decreases i n d e n s i t y w i t h i n c r e a s i n g h e i g h t , microwaves do not t r a v e l i n a s t r a i g h t l i n e , but in s t e a d f o l l o w a path which i s very n e a r l y the arc of a c i r c l e with r a d i u s about 1.33 times that of the earth (the f a c t o r depends on atmospheric c o n d i t i o n s but g e n e r a l l y l i e s between 1.1 and 23 du* to ground eluttor ond t f t t c t of ( i d * lobe* Figure 3.9 - Cone of s i l e n c e 1.6) [ B a t t 5 9 ] . When the temperature and humidity g r a d i e n t s d e v i a t e from normal c o n d i t i o n s , such as during an i n v e r s i o n , anomolous propogation occurs. S u p e r r e f r a c t i o n i s abnormal downward bending of the beam, while abnormal upward bending i s termed s u b r e f r a c t i o n . Both of these phenomena lead to s p a t i a l d i s t o r t i o n of the p r e c i p i t a t i o n measurements, but excessive s u p e r r e f r a c t i o n i s more i n s i d i o u s , since echoes from the ground some dis t a n c e from the radar s i t e are p o s s i b l e ( f i g . 3.10). Another problem i s d u c t i n g : under c e r t a i n atmospheric c o n d i t i o n s the beam may be channeled i n a duct which ac t s as a wave guide and d i r e c t s the beam long d i s t a n c e s w i t h i n a narrow l a y e r near the surface of the e a r t h . The l a s t source of measurement e r r o r to be considered i s the " b r i g h t band" e f f e c t . In the area j u s t below the f r e e z i n g l e v e l the i n t e n s i t y of radar echoes may increase by s e v e r a l orders of magnitude, due p r i m a r i l y to the melting of the 24 g r o u n d Figure 3.10 - S u p e r r e f r a c t i o n of the radar beam hydrometeors (which changes t h e i r r e f l e c t i v i t y and t e r m i n a l v e l o c i t y ) [ B a t t 5 9 ] . The p o t e n t i a l sources of e r r o r and measurement l i m i t a t i o n s o u t l i n e d combine to s i g n i f i c a n t l y reduce the accuracy of data obtained from the radar system. Some, such as the e f f e c t s of ground c l u t t e r , s i d e lobes, and the cone of s i l e n c e , are temporally and s p a t i a l l y i n v a r i a n t , and thus r e l a t i v e l y easy to c o r r e c t [Geot76], [Aoya78], [Tate78]. R e s o l u t i o n problems due to beam width, pulse l e n g t h , and range are more d i f f i c u l t to overcome, but are determinate and can be taken i n t o account. However, the e f f e c t s of a t t e n u a t i o n , m e t e o r o l o g i c a l phenomena, and anomolous propogation are f u n c t i o n s of both space and time, and are exceedingly d i f f i c u l t to adjust f o r [Orms72]. The " s u c c e s s f u l implementation of radar i n t o a p r e c i p i t a t i o n measurement system r e q u i r e s that c a r e f u l e l e c t r o n i c c a l i b r a t i o n procedures be followed and that an independent check of system biases be made by comparing radar estimates with r a i n gauge or disdrometer measurements. Data users should be cognizant of those c o n d i t i o n s i n which the radar r a i n f a l l may be erroneous or have l i t t l e v a lue. The search f o r systematic e r r o r 25 patterns holds promise, but u n t i l such p a t t e r n s can be unabiguously e s t a b l i s h e d i t w i l l be necessary to use gauges to adjust the radar" [Wils79]. 3.6 D i g i t a l Techniques f o r Q u a n t i t a t i v e R a i n f a l l Measurement E a r l y radar measurements of p r e c i p i t a t i o n were made by studying images on plan p o s i t i o n i n d i c a t o r (PPI) or range height i n d i c a t o r (RHI) scopes. With t h i s equipment, the video s i g n a l from the radar was processed t o produce an analog d i s p l a y with a r e f r e s h l i n e moving on the screen to match the t r a v e l of the antenna. The s i g n a l s returned by the hydrometeors e x h i b i t s i g n i f i c a n t f l u c t u a t i o n s i n i n t e n s i t y , caused by rearrangement of the p a r t i c l e s due both to movement of the hydrometeors with respect to each other and movement of the whole mass r e l a t i v e to the radar [ B a t t 5 9 ] . With the i n t r o d u c t i o n of d i g i t a l p rocessing of radar s i g n a l s , some method of averaging or i n t e g r a t i n g the sequence of pulse returns i s r e q u i r e d (the p e r s i s t e n c e of the screen phosphor has the e f f e c t of averaging the s i g n a l i n an analog d i s p l a y [Croz75]). A device c a l l e d the d i g i t a l video i n t e g r a t o r processor (DVIP) has been developed which converts the input analog s i g n a l s to d i g i t a l radar echo i n t e n s i e s . The inputs to the processor are l o g a r i t h m i c radar video together with antenna s y n c h r o n i z a t i o n i n f o r m a t i o n . The processor r e c u r s i v e l y f i l t e r s the incoming s i g n a l , a p p l i e s a di s t a n c e n o r m a l i z a t i o n 26 c o r r e c t i o n , samples i n d i s c r e t e range i n t e r v a l s , and t r a n s l a t e s i t t o d i g i t a l form. Output i s i n the form of in t e g r a t e d d i g i t a l i n t e n s i t y values f o r each b i n (a volume of space s p e c i f i e d by a f i x e d range, azimuth, and e l e v a t i o n angle) [Glov72]. A p r e c i p i t a t i o n map can be generated from t h i s s p a t i a l l y referenced i n t e n s i t y data by c o n s t r u c t i n g a constant a l t i t u d e plan p o s i t i o n i n d i c a t o r (CAPPI). A CAPPI i s produced by combining i n t e n s i t y values from segments of p r o g r e s s i v e l y lower angle PPI's with i n c r e a s i n g range to generate an image corresponding to a roughly constant a l t i t u d e , a l l o w i n g f o r curvature of the earth ( f i g . 3.11). Beyond that d i s t a n c e Range a l l o w a n c e gate for curvoture of the eorth Figure 3.11 - CAPPI Construction from the radar where the lowest beam angle i n t e r s e c t s the CAPPI e l e v a t i o n , the CAPPI becomes equivalent to a PPI. The 27 advantage of using a CAPPI f o r p r e c i p i t a t i o n s t u d i e s i s that the e f f e c t s of the v a r i a t i o n i n r a i n f a l l i n t e n s i t y due to changing measurement height are reduced, and i n a d d i t i o n i t i s not as a f f e c t e d by the problems of ground c l u t t e r near the radar as a low e l e v a t i o n angle PPI. 3.7 The SCEPTRE Radar Atmospheric Environment S e r v i c e s operates a number of weather radar systems across Canada ( f i g . 3.12). The most Figu r e 3.12 - AES weather radar i n s t a l l a t i o n s i n Canada r e c e n t l y developed o p e r a t i o n a l system, SCEPTRE (System f o r Constant E l e v a t i o n P r e c i p i t a t i o n Transmission and REcording), 28 i s a network of r a i n f a l l measurement radars which produce r e a l time CAPPI's and record p r e c i p i t a t i o n f o r a r c h i v e purposes. SCEPTRE i n s t a l l a t i o n s are remotely s i t e d f i v e cm radars which operate unattended (with r o u t i n e weekly s e r v i c i n g ) , t r a n s m i t t i n g CAPPI f a c s i m i l e s to the nearest AES weather c e n t r e . Remote operation allows a choice of s i t e which gives the best coverage of the area independent of the l o c a t i o n of the weather o f f i c e . The SCEPTRE u n i t c o n s i s t s of the radar i t s e l f together with c o n t r o l and data processing equipment and software ( f i g . 3.13). t r a n s n l t t v r dup1«x«r wav*0u1d« c o m p o n e n t s I RADAR CONTROL CENTRE P P I a n d c o n t r o l c o n a o 1 a c o n t r o l a n d d a t a p r o c a a a l n g a l n l c o a p u t a r t a p a a r c M v a f a c a l M l I t a a c h l n a PROCESSOR CONTROL CENTRE Figure 3.13 - SCEPTRE radar schematic Each i n s t a l l a t i o n has a 250 kW Raytheon WSR-807 radar 29 ( t a b l e 3.2) housed i n a weather-proof radome atop a f i f t e e n T r a n s m i t t e r : Wavelength Frequency Nominal Peak Power Pulse Length Pulse Repetition Frequency Receiver: Receiver System Minimum Detectable Signal Dynamic Range Antenna: Reflector Type Reflector Diameter Feed Type Feed P o l a r i z a t i o n Gain Side Lobe Level Scan Rate Elev a t i o n Range Radome General: Minimum Detectable Z Minimum Detectable R 5.3 cm 5.450-5.825 GHz 250 kW 2.0 ± 0.1 „s 324 ± 1 logar1thmlc -104 dB 80 dB paraboloid 3.658 m horn vert1ca1 43 dB -25 dB 6 rpm -2.5' to 45' 5.8 m diameter p l a s t i c on aluminum space frame 13 dB 0.2 mm/hr Table 3.2 - Raytheon WSR-807 radar s p e c i f i c a t i o n s metre s t e e l tower ( f i g . 3.14). The radar t r a n s m i t t e r and r e c e i v e r equipment ( f i g . 3.15) are l o c a t e d i n an enclosure on the tower, with the antenna d i s h and pedastal mount ( f i g . 3 . 1 6 ) i n the radome on the f l o o r above. A small b u i l d i n g on s i t e s h e l t e r s the PPI i n d i c a t o r and c o n t r o l console ( f o r manual operation) ( f i g . 3.17) as w e l l as a DEC PDP-11/35 minicomputer which monitors and c o n t r o l s the operation of the system and processes the d i g i t a l radar s i g n a l s ( f i g . 3 . 1 8 ) . Computing Devices Company provided the DVIP and other s p e c i a l i z e d s i g n a l processing and system c o n t r o l hardware. Each s i t e a l s o has a f a c s i m i l e machine to d i s p l a y the CAPPI's being t r a n s m i t t e d to the l o c a l weather o f f i c e ( f i g . 3.17), 30 F i g u r e 3.14 - Radar tower and c o n t r o l b u i l d i n g a t the A b b o t s f o r d SCEPTRE s i t e and two 9 - t r a c k magnetic tape d r i v e s used f o r l o a d i n g the system s o f t w a r e and r e c o r d i n g the a r c h i v e d a t a . The r e a l time computer d a t a p r o c e s s i n g and c o n t r o l system a r e what d i s t i n g u i s h e s t h e SCEPTRE network - the r a d a r equipment i t s e l f i s not v e r y d i f f e r e n t from t h a t found i n many o t h e r f i v e cm r a d a r systems. The PDP-11 minicomputer p r o c e s s e s the DVIP o u t p u t u s i n g a h i e r a r c h y of t h r e e scan s t a g e s . The A scan i s a s i n g l e p u l s e r e t u r n c o r r e s p o n d i n g t o one e l e v a t i o n and a z i m u t h a n g l e . The summation of A scans 31 Figure 3.15 - Transmitter, receiver, and antenna control equipment over one complete revolution of the antenna i s one B scan (a single A scan i s shown on the oscilloscope ( f i g . 3.19) while the PPI displays the B scan). With a pulse re p e t i t i o n frequency of 324 pulses per second and an antenna period of ten seconds, there are 3240 A scans per B scan, or nine per degree of azimuth. A complete three dimensional survey of the p r e c i p i t a t i o n i s a C scan, made up of a set of B scans, each at a predetermined elevation angle. The SCEPTRE system normally uses a cycle of twenty-nine B scans to produce three C scans which correspond to p a r t i c u l a r DVIP operational 32 I F i g u r e 3.16 - 3.66 m d i a m e t e r p a r a b o l i c antenna and p e d a s t a l mount s e t t i n g s and ranges ( t a b l e 3.3) [CDC 7 9 a ] . The system has a twenty minute p r o c e s s i n g c y c l e which i s d i v i d e d i n t o two t e n minute o p e r a t i o n p e r i o d s . D u r i n g each p e r i o d , d a t a i s a c q u i r e d , p r o c e s s e d , and a r c h i v e d , and two CAPPI c h a r t s a r e produced and t r a n s m i t t e d ( f i g . 3.20) [CDC 79b]. The g e n e r a t i o n of the r e a l - t i m e CAPPI c h a r t s and the a r c h i v i n g of the d a t a on 9 - t r a c k tape a r e independent o p e r a t i o n s , and d i f f e r e n t s o u r c e d a t a i s used f o r each. A l a r g e p o r t i o n of t h e a v a i l a b l e minicomputer p r o c e s s o r t i m e i s used t o produce t h e r e a l - t i m e CAPPI's. Of the n i n e A scans r e c e i v e d d u r i n g t h e time t h e antenna sweeps one a z i m u t h a l degree, e i g h t a r e used as CAPPI d a t a , but the computer a c t u a l l y p r o c e s s e s o n l y a p p r o x i m a t e l y one h a l f of t h e s e . The DVIP s i g n a l s f o r each s e t of e i g h t scans a r e 33 F i g u r e 3.17 - PPI i n d i c a t o r and c o n t r o l c o n s o l e a c c u m u l a t e d i n 115 r e g i s t e r s , one f o r e a c h r a n g e b i n , t h e n t h o s e v a l u e s w i t h i n t h e r a n g e g a t e s f o r t h e r e q u i r e d CAPPI a r e s t o r e d i n memory ( t a b l e 3 . 4 ) . The c o m p u t e r a l s o m o n i t o r s t h e a z i m u t h a l and e l e v a t i o n a n g u l a r p o s i t i o n o f t h e a n t e n n a , and r e c o r d s t h i s d a t a w i t h e a c h A s c a n s t o r e . I t i s programmed t o p r i n t a w a r n i n g i f t h e a n g u l a r v e l o c i t y d e v i a t e s f r o m s i x rpm by more t h a n two p e r c e n t o r t h e e l e v a t i o n a n g l e i s i n c o r r e c t by more t h a n 0.3 d e g r e e s . I f g r o s s a n t e n n a p o s i t i o n i n g e r r o r s o c c u r t h e computer s h u t s down t h e e n t i r e s y s t e m . Once t h e c o m p l e t e s e t o f B s c a n s h a s been a c q u i r e d a n d s t o r e d , s c a n 34 F i g u r e 3.18 - PDP-11/35 m i n i c o m p u t e r and s y s t e m c o n t r o l e q u i pment c o n v e r s i o n t a k e s p l a c e . The p o l a r p r e c i p i t a t i o n maps a r e c o n v e r t e d t o c a r t e s i a n c o o r d i n a t e s and t h e a r e a o f p r e c i p i t a t i o n f o r e a c h i n t e n s i t y l e v e l i s c a l c u l a t e d [CDC 7 9 b ] . An e l a b o r a t e d e c i s i o n p r o g r a m i s u s e d t o s e l e c t t h e c h a r t s p r o d u c e d a n d t r a n s m i t t e d , b a s e d on t h e t i m e o f t h e o p e r a t i n g p e r i o d and t h e amount o f p r e c i p i t a t i o n a t v a r i o u s CAPPI e l e v a t i o n s . The s y s t e m c a n g e n e r a t e c h a r t s a t CAPPI l e v e l s o f 1.5 km, 4 km, 7 km, 11 km, a n d 15 km, a s w e l l a s e c h o t o p , l o n g r a n g e ( i n summer o n l y ) , a n d h i g h s e n s i t i v i t y ( i n w i n t e r o n l y ) d i s p l a y s [ H o r i 8 0 ] . The c h a r t s , w h i c h i n c l u d e 35 F i g u r e 3.19 - O s c i l l o s c o p e showing a s i n g l e A s c a n and t h e PPI d i s p l a y C Scan B Scans Range Bin Size Normal 1 - 19 240 km 2 km Long Range 20 - 24 360 km 3 km High S e n s i t i v i t y 25 - 29 120 km 2 km T a b l e 3.3 - SCEPTRE C s c a n r a n g e a n d s e n s i t i v i t y o p t i o n s s y s t e m s t a t u s i n f o r m a t i o n and a map o v e r l a y , a r e t r a n s m i t t e d t o t h e l o c a l w e a t h e r c e n t r e o v e r a t e l e p h o n e l i n e . B e c a u s e t h e c h a r t i s s e n t i n a n a l o g mode, o n l y f o u r p r e c i p i t a t i o n l e v e l s a r e a v a i l a b l e , d e p i c t e d a s d i f f e r e n t g r e y l e v e l s [ T r y 72] ( f i g . 3 . 2 1 ) . No s o f t w a r e was i n c l u d e d i n t h e 36 Data Acqulaltlon (B Scana) PROCESSING CYCLE TIMING Data Acquisition (B Scana) Data Procaaalng Scan Convaralon UChart Production Chart Transnlsalon '•t Operating Parlod 2nd Oparatlng Parlod 10 Tlaa (alnutaa) ao Figure 3.20 - Processing c y c l e t i m i n g chart S c a n E l e v a t i o n Normal CAPPI Range G a t e S e t t I n g s N o . A n g l e 1 .5 km 4 . 0 km 7 . 0 km 1 1 . 0 km 1 5 . 0 km ( d e g r e e s ) (km) (km) (km) (km) (km) 1 0 . 5 0 92 - 240 190 _ 240 2 0 80 72 - 92 146 - 190 224 - 240 3 1 19 54 - 72 130 - 146 198 - 224 4 1 6 0 44 - 54 102 - 130 166 - 198 236 - 240 5 2 10 34 - 44 88 - 102 142 - 166 208 - 236 6 2 60 30 - 34 72 - 88 122 - 142 180 - 208 234 - 240 7 3 19 24 - 30 62 - 72 104 - 122 156 - 180 204 - 234 8 3 88 20 - 24 52 - 62 88 - 104 132 - 156 176 - 204 9 4 69 18 - 20 44 - 52 74 - 88 116 - 132 152 - 176 10 5 60 14 - 18 38 - 44 64 - 74 98 - 116 132 - 152 11 6 69 12 - 14 30 - 38 54 - 64 84 - 98 112 - 132 12 7 88 28 - 30 46 - 54 72 - 84 98 - 1 12 13 9 30 22 - 28 40 - 46 62 - 72 82 - 98 14 11 10 20 - 22 32 - 40 52 - 62 72 - 82 15 13 19 16 - 20 30 - 32 44 - 52 58 - 72 16 16 10 12 - 16 22 - 30 36 - 44 50 - 58 17 19 69 20 - 22 30 - 36 40 - 50 18 2 5 . 88 16 - 20 26 - 30 34 - 40 19 2 9 . OO 12 - 16 12 - 26 18 - 34 Table 3.4 - Normal CAPPI c o n s t r u c t i o n t a b l e : range gate s e t t i n g s and corresponding e l e v a t i o n angles SCEPTRE system to remove s t a t i o n a r y echoes, so rectangular grey areas were added to the overlay map to mask regions from 37 F i g u r e 3.21 - An example o f a CAPPI f a c s i m i l e f r o m t h e A b b o t s f o r d SCEPTRE i n s t a l l a t i o n 38 which ground echoes were received. One complete archive record i s written on magnetic tape during each operating period. This record contains system status flags as well as DVIP and antenna po s i t i o n data. Every ni-nth A scan i s used as the source of the archive data, with a l l two km range bins recorded which l i e within preset upper and lower elevation gate settings (twenty-two and zero km respectively) for each elevation angle [CDC 79b]. The data i s written at 1600 bpi on 730 m 9-track magnetic tapes which are forwarded to AES headquarters near Toronto for storage. Records from th i s archive of operational p r e c i p i t a t i o n data for the f i v e SCEPTRE radars are available to the public from AES [AES 81]. 39 CHAPTER IV RADAR-DERIVED PRECIPITATION MEASUREMENTS OVER THE VANCOUVER AREA 4/1 I n t r o d u c t i o n Data obtained from an o p e r a t i o n a l p r e c i p i t a t i o n measuring radar near Abbotsford provided the ba s i s f o r the a n a l y s i s i n t h i s chapter. The source of t h i s information and inherent e r r o r s i n the images deri v e d from i t are discussed. The radar measurements are c o r r e l a t e d with raingauge data and the r e s u l t s of t h i s comparison of a r e a l and point measurements are considered. The chapter concludes with a d e s c r i p t i o n of the image d i s p l a y system used and the pat t e r n s seen i n the images produced. 4.2 The Abbotsford SCEPTRE Radar I n s t a l l a t i o n Continuous s p a t i a l p r e c i p i t a t i o n observations f o r the Vancouver area became a v a i l a b l e i n l a t e 1978 when the Abbotsford SCEPTRE radar began o p e r a t i o n . Located f i v e km due south of Aldergrove, B.C. (at 49° 0' 56" l a t i t u d e , 122° 29' 11" longitude [Hans82]), the radar scans a 240 km radius area which encompasses the lower mainland, Gulf i s l a n d s , the southern p o r t i o n of Vancouver I s l a n d , and northwestern Washington State ( f i g . 4.1). This radar i s i d e a l l y s i t e d f o r r a i n f a l l measurements over greater Vancouver since the 40 Figure 4 .1 - Location of the Abbotsford SCEPTRE radar with cone of s i l e n c e and 20 km range r i n g s marked metrop o l i t a n area l i e s between f i f t e e n and s i x t y - f i v e km from the radar: outside the twelve km radius cone of s i l e n c e and i n s i d e the range of the 1 .5 km true CAPPI. However, p r e c i p i t a t i o n measurement i s obscured over a l a r g e p o r t i o n of the area w i t h i n 240 km by i n t e r v e n i n g mountains, with the r e s u l t that useable records are a v a i l a b l e f o r only a r e l a t i v e l y small area ( f i g . 4 . 2 ) . 4 . 3 Data Obtained from the AES Archive A l l SCEPTRE radar tapes r e c e i v e d at AES headquarters are processed to ensure a standard format and q u a l i t y c o n t r o l before they enter the a r c h i v e . Incoming records are checked f o r both radar and processor c o n s i s t e n c y by procedures such as 41 Figure 4.2 - Coverage of 2 km CAPPI s t a t i s t i c a l l y a n a l y z i n g the recorded b i t patterns and comparing adjacent bins and scans, both h o r i z o n t a l l y and v e r t i c a l l y , to detect anomolous c o n d i t i o n s . Data which i s suspected to be i n e r r o r i s not c o r r e c t e d or d e l e t e d , but i s flagged and enters the a r c h i v e . Monthly e r r o r summaries are compiled f o r each radar s i t e [Hogg78]. Radar p r e c i p i t a t i o n records f o r s e v e r a l of the most severe storms over the Vancouver area from the time the system became o p e r a t i o n a l i n 1978 to the f a l l of 1981 were requested 42 from AES. Due t o radar and/or computer malfunctions, data f o r most of these storms was not a v a i l a b l e (the Abbotsford SCEPTRE radar was unserviceable f o r a major p o r t i o n of the f i r s t two years of i t s o p e r a t i o n ) . P a r t i a l storm records were obtained for f i v e events between December 1979 and March 1981 (ta b l e 4.1). 1. 0004 GMT 12 Dec 1979 to 0624 GMT 12 Dec 1979 - 0 missing records 2216 GMT 12 Dec 1979 to 1114 GMT 14 Dec 1979 - 3 missing records 2. 1204 GMT 25 Dec 1979 to 0004 GMT 28 Dec 1979 - 14 missing records 3. 0O04 GMT 10 Jul 1980 to 2124 GMT 10 Jul 1980 - 0 missing records 4. 2354 GMT 19 Dec 1980 to 1954 GMT 22 Dec 1980 - 0 missing records 5. O004 GMT 11 Feb 1981 to 0244 GMT 16 Feb 1981 - 0 missing records 1944 GMT 17 Feb 1981 to 2354 GMT 18 Feb 1981 - 0 missing records Table 4.1 - Storm records received from AES The data from the ar c h i v e was processed i n t o CAPPI images by AES. Processing d i f f i c u l t i e s prevented standard 1.5 km CAPPI's from being produced which had complete coverage of the area, so AES chose to generate CAPPI's f o r an e l e v a t i o n of 2000 m f o r t h i s p r o j e c t . This n e c e s s i t a t e d the c a l c u l a t i o n of a new CAPPI c o n s t r u c t i o n t a b l e ( t a b l e 4.2). CAPPI images were con s t r u c t e d on a two km square c a r t e s i a n g r i d over the 240 km radius range using the a r c h i v e d A scan records, one f o r each ten minute operating p e r i o d . These were formulated i n t o a 240 x 240 matrix c o n t a i n i n g the c i r c u l a r scan area, t o which was added a header f i e l d c o n t a i n i n g the time and date of the measurement, and then w r i t t e n onto 1600 bpi magnetic tape. AES r e q u i r e d s e v e r a l months to complete the processing of a l l the data that was requested f o r t h i s study. 43 Elevation Angle Range Gate Settings (degrees) (km) 0 . 5 0 114 - 240 0 . 8 0 8 6 - 1 1 4 1 . 19 68 - 86 1 . 6 0 56 - 68 2 . 10 44 - 56 2 . 6 0 38 - 44 3 . 19 32 - 38 3 . 8 8 2 6 - 3 2 4 .69 2 2 - 2 6 5 . 6 0 18 - 22 6 . 6 9 14 - .18 Table 4.2 - 2 km CAPPI c o n s t r u c t i o n t a b l e [Hans82] The CAPPI g r i d s , which were received on tape i n the form of DVIP s i g n a l i n t e n s i t i e s , were converted i n t o p r e c i p i t a t i o n i n t e n s i t i e s ( i n mm/hr) based on the c a l i b r a t i o n t a b l e f o r the SCEPTRE radar ( t a b l e 4.3) (For the Abbotsford radar the noise Detection Level DVIP Intensity Value P r e c i p i t a t i o n Rate (mm/hr) 0 0 - 7 0 1 8 - 15 0 . 25 2 16 - 23 0 . 5 3 24 - 31 1 4 32 - 39 2 5 40 - 47 4 6 48 - 55 8 7 56 - 63 16 8 64 - 71 32 9 72 - 79 64 10 80 - 87 128 11 88 - 95 256 12 96 - 103 512 13 104 - 111 1024 14 112 - 119 15 120 - 127 Table 4.3 - SCEPTRE DVIP s i g n a l - r a i n f a l l i n t e n s i t y c a l i b r a t i o n [Sauv8l] t h r e s h o l d has been set at the DVIP s i g n a l l e v e l of twenty-six, which corresponds to a minimum detectable p r e c i p i t a t i o n i n t e n s i t y of about one mm/hr.) Over 2000 image g r i d s were 44 re c e i v e d , representing a t o t a l of 337 hours of r a i n f a l l measurements f o r the f i v e storm events. 4.4 E r r o r s i n CAPPI Data " When the CAPPI images were d i s p l a y e d , s e v e r a l e r r o r s became apparent. These e r r o r s came from two sources: those i n the o r i g i n a l radar measurements and those introduced during the CAPPI processing by AES. The a n a l y s i s and attempted c o r r e c t i o n of these problems r e q u i r e d a considerable expenditure of e f f o r t . The most obvious e r r o r was the presence of c i r c u l a r r i n g s of higher i n t e n s i t y p r e c i p i t a t i o n . These were p a r t i c u l a r l y n o t i c e a b l e i n the cumulative r a i n f a l l p a t t e r n s f o r the storm events which were generated by summing the ten minute i n t e n s i t i e s over the du r a t i o n of the storm and d i s p l a y i n g as a h y e t a l surface ( f i g . 4.3). The c o n c e n t r i c nature of the r i n g s , centred on the radar s i t e , and the di s t a n c e s at which the peaks occurred, i n d i c a t e d that they were an a r t i f a c t introduced during the c o n s t r u c t i o n of the CAPPI. Since the o r i g i n a l radar r e t u r n s i g n a l s were not a c c e s s i b l e , the only remedial a c t i o n a v a i l a b l e was to attempt to c o r r e c t the alre a d y processed data. I t was assumed that the r i n g s were caused by the v a r i a t i o n s i n the height at which the p r e c i p i t a t i o n measurements were made, and c o r r e c t i o n was attempted on t h i s b a s i s . This was p o s s i b l y due to a p o r t i o n of the r a i n f a l l 45 Figure 4.3 - Uncorrected cumulative r a i n f a l l p a t t e r n f o r the December 1980 storm forming i n the v i c i n i t y of the CAPPI a l t i t u d e , r e s u l t i n g i n more p r e c i p i t a t i o n being measured below the CAPPI e l e v a t i o n than above i t . The e l e v a t i o n s of the two km CAPPI measurements, c o r r e c t e d f o r the curvature of the earth and standard beam r e f r a c t i o n (appendix A), vary between a minimum 46 of 1636 m a t a range of fourteen km and 5835 m at 240 km (the two km CAPPI i s e f f e c t i v e l y a 0.5 degree PPI beyond a range of 125 km). A number of d i f f e r e n t c o r r e c t i o n procedures were t r i e d , i n c l u d i n g attempts to vary the amount of c o r r e c t i o n with the d i s t a n c e from the radar, but the most s u c c e s s f u l a l g o r i t h m used a m u l t i p l i c a t i v e f a c t o r based s o l e l y on the r a t i o of the a c t u a l measurement a l t i t u d e to the nominal CAPPI e l e v a t i o n ( f i g . 4.4 and 4.5). Although the value of the c o r r e c t i o n f a c t o r was c l o s e to one ( i n the range 0.9 to 1.1 f o r the working image a r e a ) , the r a i n f a l l i n t e n s i t y values changed by a c o n s i d e r a b l e amount because t h i s f a c t o r was a p p l i e d to the DVIP readings, to which r a i n f a l l i n t e n s i t y i s r e l a t e d e x p o n e n t i a l l y . A p r o f i l e of the uncorrected cumulative r a i n f a l l at an azimuth of 270° from the radar ( f i g . 4.6) shows the l a r g e v a r i a t i o n s i n the amount of p r e c i p i t a t i o n measured. An improvement i s noted i n the c o r r e c t e d p r o f i l e f o r the same storm which has a s i g n i f i c a n t r eduction i n the v a r i a t i o n . The true c o r r e c t e d p r o f i l e i s not known but would be f r e e of the systematic r i n g p a t t e r n s . As can be seen, t h i s a l g o r i t h m does not completely remove the p e r i o d i c i n t e n s i t y s p i k e s , but i t does reduce them and i s more e f f e c t i v e with i n c r e a s i n g range. More work would be r e q u i r e d to o b t a i n a complete c o r r e c t i o n method, but t h i s i s not warranted without access t o the o r i g i n a l data as i t can best be e l i m i n a t e d when 47 Figure 4.4 - Convolution p a t t e r n f o r image c o r r e c t i o n the CAPPI's are generated. For example, by t a k i n g a weighted average of values from bins above and below the CAPPI a l t i t u d e , i t might be p o s s i b l e t o co n s t r u c t an image free from t h i s systematic e r r o r . A second problem with the data was the appearance of strong s t a t i o n a r y echos i n the images. The p o s i t i o n of these echos matched the l o c a t i o n s of nearby mountains with e l e v a t i o n s great enough to block the radar beam at the CAPPI e l e v a t i o n ( f i g . 4.7). No c o r r e c t i o n was made f o r t h i s source 48 Figure 4.5 - Corrected cumulative r a i n f a l l p a t t e r n f o r the December 1980 storm of e r r o r because these anomolies were e a s i l y i d e n t i f i e d i n the images and do not occur i n the urban areas, which were the prime regions of i n t e r e s t i n t h i s study. This problem has been overcome i n other radar a p p l i c a t i o n s , such as a i r t r a f f i c c o n t r o l , by processing the radar s i g n a l s to r e j e c t non-moving t a r g e t s . The s o l u t i o n to t h i s problem i s f o r AES to add moving t a r g e t i n d i c a t o r (MTI) a n a l y s i s to t h e i r processing software at each SCEPTRE i n s t a l l a t i o n . P r i o r removal of 49 DECEMBER 20 -2 2 Z < d —I w> 2 O o i 1 1 1 1 1 1 1 r UNCORRECTED PROFILE CORRECTED PROFILE 22 1980 STORM — i — i — T -i 1 r J L _l L - I 1 1 L _ l L - J 1 I L 0.0 tOX 20.0 30.0 40.0 50.0 60.0 70.0 80.0 DISTANCE FROM RADAR SITE (KM) 90.0 WO.0 Figure 4.6 - Comparison of c o r r e c t e d and uncorrected cumulative p r o f i l e s f o r December 1980 storm s t a t i o n a r y echoes would be e s s e n t i a l f o r any subsequent s p a t i a l or s t a t i s t i c a l a n a l y s i s by a user of t h i s data. In a d d i t i o n t o the long periods of missing records which occurred when the Abbotsford radar was completely shut down, there were a l s o numerous short i n t e r v a l s , between ten minutes and s e v e r a l hours d u r a t i o n , when no data was recorded. Several of these i n t e r v a l s occurred during the storm events f o r which records were r e c e i v e d , r e s u l t i n g i n gaps of one to twelve images i n the sequences. A few of the records had i n c o r r e c t times or dates, but t h i s minor problem was easy to c o r r e c t when the images were processed here. Another small 50 Figure 4 .7 - Locations of s t a t i o n a r y echoes e r r o r was the existance of h a l f images at the end of two of the sequences, presumably due to processing e r r o r s by AES. These problems would most c e r t a i n l y f r u s t r a t e any attempt to automated processing of t h i s data i n i t s present form. Accurate reading of the three CAPPI data tapes provided by AES proved to be another d i f f i c u l t y . A l a r g e number of data e r r o r s on a l l three tapes caused i n c o n s i s t e n t i n t e r p r e t a t i o n of the images. Comparison of two copies of the same image read from tape on separate occasions revealed d i f f e r i n g values of some of the i n d i v i d u a l measurements, and what was more s e r i o u s , i n about one percent of the cases a p o r t i o n of the record was completely m i s s i n g . This problem was caused when the tapes were w r i t t e n at AES, and was due e i t h e r to using very o l d tapes or w r i t i n g on a d i r t y tape 51 d r i v e . This poor q u a l i t y data processing does not appear to be c o n s i s t e n t with the investment i n v o l v e d i n a l l of the p r i o r phases of the a c q u i s i t i o n of t h i s i n f o r m a t i o n . 4 .5 Comparison with Rain Guaqe Records To v e r i f y the accuracy of the radar measurements and i n v e s t i g a t e the r e l a t i o n s h i p between s p a t i a l l y - a v e r a g e d and point-source p r e c i p i t a t i o n data, the radar-derived estimates of r a i n f a l l were compared with raingauge measurements. From s t u d i e s by other authors, i t was expected that the radar would, on average, sense l e s s r a i n f a l l than that measured i n the gauges, and that the magnitude of t h i s discrepancy would vary from storm to storm and increase w i t h d i s t a n c e from the radar s i t e . These trends were a l s o observed i n t h i s study. The area w i t h i n which t h i s comparison was undertaken encompassed the lower mainland, Gulf i s l a n d s , and southeastern Vancouver I s l a n d . D a i l y a c c u l u l a t i o n s were chosen as the b a s i s f o r the comparison because of the p a u c i t y of gauges with recording frequencies of l e s s than twenty-four hours w i t h i n t h i s area and because random v a r i a t i o n s tend to dominate over shorter p e r i o d s , making the comparison l e s s meaningful. Five days of d a i l y records were obtained from the AES Monthly  Record of M e t e o r o l o g i c a l Observations i n Western Canada fo r ninety-seven s t a t i o n s i n B r i t i s h Columbia ( f i g . 4 . 8 ) . The l a t i t u d e and longitude of each s t a t i o n (given i n the AES  Monthly Record of M e t e o r l o l o g i c a l Observations i n Canada 52 Figure 4.8 - Location of AES raingauge s t a t i o n s with d a i l y records Supplement) were converted to U n i v e r s a l Transverse Mercator (UTM) coordinates by l o c a t i n g each s t a t i o n on a 1:50 000 s c a l e topographic map. This coordinate system served as the reference g r i d f o r the comparison with the radar data. The radar values were obtained by summing over 144 ten minute i n t e n s i t i e s (beginning with the record f o r 0804 l o c a l time one day and ending with the 0754 record on the next - t h i s corresponded to the observation p e r i o d f o r the d a i l y raingauge data) and d i v i d i n g the t o t a l by s i x . For comparison purposes, the radar measurement was taken as the value f o r the two-k i l o m e t r e square which contained the p o i n t gauge. The raingauge and corresponding radar data are summarized i n appendix B. To analyze the c o r r e l a t i o n between the radar and raingauge values, l i n e a r r e gressions were computed for f i v e 53 days of data ( f i g . 4.9 through 4.13). In each case the S RADAR/RAINGAUGE CORRELATION - DECEMBER 20 1980 2 2 < or < o < cr ~i i 1 1 1 1 1 1 1 1 1 1 1 r NUMBER OF OBSERVATIONS = 81 CORRELATION COEFFICIENT = 0.737 STANDARD ERROR OF ESTIMATE = 4.208 "i 1 1 r - 1 1 1 1 1 1 1 1 1 1 i i i • t i i • • 0 8 B 24 S2 40 48 5 6 ' 64 72 80 RAINGAUGE MEASUREMENT (MM) Figure 4.9 - Radar/raingauge r e g r e s s i o n r e l a t i o n s h i p f o r 20 December 1980 comparison * was based on about eighty o b s e r v a t i o n s . The c o r r e l a t i o n c o e f f i c i e n t s ranged between 0.665 and 0.737, i n d i c a t i n g t h a t a strong c o r r e l a t i o n e x i s t e d but a l s o that there was s i g n i f i c a n t v a r i a t i o n from the best f i t l i n e . The standard e r r o r of estimate ( l i m i t s of d e v i a t i o n from the 54 R A D A R / R A I N G U A G E C O R R E L A T I O N - D E C E M B E R 2 1 1 9 8 0 s j — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — _ NUMBER OF OBSERVATIONS = 81 p _ CORRELATION COEFFICIENT = 0.665 . STANDARD ERROR OF ESTIMATE = 2.524 ie _ ' 2 ui U i e I 1 I 1 I 1 1 1 I I I I I I I I I I I I I 0 B 16 24 32 40 48 56 64 72 60 RAINGAUGE MEASUREMENT (MM) Figure 4.10 - Radar/raingauge r e g r e s s i o n r e l a t i o n s h i p f o r 21 December 1980 reg r e s s i o n l i n e w i t h i n which about two-thirds of the observations f a l l ) ranged from 2.3 to 5.8 mm. In a l l cases the radar over-estimated l i g h t r a i n f a l l s and under-estimated heavy ones, which i s c o n s i s t e n t with the f i n d i n g s of Wilson and Brandes [ W i l s 7 9 ] , The three-dimensional h y e t a l surface r e p r e s e n t a t i o n s f o r both the radar and raingauge data f o r 20 December 1980 ( f i g u r e 55 S RADAR/RAINGAUGE CORRELATION -to < or; < < or I I I 1 1 1 1 1 1 1 1— NUMBER OF OBSERVATIONS = 80 CORRELATION COEFFICIENT = 0.711 STANDARD ERROR OF ESTIMATE = 2.293 FEBRUARY 12 1981 — i — i — "i 1 r - i — i — i — i — i — i ' • • • - j — i — i — i — i i ' i 24 32 40 48 56 RAINGUAGE MEASUREMENT (MM) 64 72 80 Figure 4.11 - Radar/raingauge r e g r e s s i o n r e l a t i o n s h i p f o r 12 February 1981 4.14) serve t o i l l u s t r a t e the complexity of the c o r r e l a t i o n problem. The upper, r a d a r - d e r i v e d image was computed using only one-quarter of the 6300 i n d i v i d u a l measurements radar took over the area, and shows s i g n i f i c a n t v a r i a t i o n between adjacent p o i n t s (the very high spikes are echos from mountains, not r a i n f a l l measurements). The lower p i c t u r e , computed from the i r r e g u l a r p a t t e r n of eighty-one l o c a t i o n s at which gauge measurements were taken, i s n a t u r a l l y much 5 6 8 R A D A R / R A I N G A U G E C O R R E L A T I O N - F E B R U A R Y 13 1 9 8 1 2> 2 "T 1 1 1 1 1 1 1 1 1 1— NUMBER OF OBSERVATIONS = 76 CORRELATION COEFFICIENT = 0.685 STANDARD ERROR OF ESTIMATE = 3.390 i 1 1 1 1 1 1—~r -i 1 1—-—t 1 1 i I I J I L 24 52 40 48 56 RAINGAUGE MEASUREMENT (MM) 72 80 Figure 4.12 - Radar/raingauge r e g r e s s i o n r e l a t i o n s h i p f o r 13 February 1981 smoother because, on average, the measurement l o c a t i o n s are more than three times f u r t h e r apart than those of the radar. The raingauge surface i n c l u d e s l e s s area because no values were obtained f o r Washington State nor over regions of open water. Despite the much rougher surface t e x t u r e of the radar p i c t u r e and the area of missi n g data due to the cone of s i l e n c e , the o v e r a l l p a tterns of s p a t i a l v a r i a t i o n agree, as was expected. To obtai n the same l e v e l of point to point 57 RADAR/RAINGAUGE CORRELATION - FEBRUARY 14 1981 s i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — . NUMBER OF OBSERVATIONS = 76 ~ . CORRELATION COEFFICIENT = 0.713 _ STANDARD ERROR OF ESTIMATE = 5.848 •* _ 2 2 0 8 16 24 32 40 48 56 64 72 80 RAINGAUGE MEASUREMENT (MM) Figure 4.13 - Radar/raingauge r e g r e s s i o n r e l a t i o n s h i p f o r 14 February 1981 v a r i a t i o n d e t a i l s seen i n the radar p i c t u r e , the raingauge network d e n s i t y would have to be increased f o r t y f o l d . The r a t i o s of gauge to radar r a i n f a l l depth estimates were computed f o r the f i v e days of data ( t a b l e 4.4). The o v e r a l l average value of 1.76 i s g e n e r a l l y l a r g e r than that found by other researchers, but the amount of day-to-day v a r i a t i o n i n t h i s r a t i o i s not. In a study of fourteen storms 58 Figure 4.14 - Hyetal surface representations of radar and raingauge data f o r 20 December 1980 i n Oklahoma using a ten cm radar, Wilson and Brandes [Wils79] found an average r a t i o of 1.04, but measured r a t i o s as low as 0.41 and as high as 2.41, i n d i c a t i n g a great deal of v a r i a t i o n on a storm-to-storm b a s i s , and l i t t l e i n d i c a t i o n of day-to-day c o r r e l a t i o n . They report that " l a r g e wanderings i n the gauge to radar r a t i o s are not unexpected i n view of the observed 59 D a t e N o . o f V a l u e s G/R Mean C o e f f . o f V a r i a t i o n 20 Dec 1980 81 1 .734 O .284 21 Oec 1980 81 2 . 146 0 .445 12 Feb 1981 80 1 .729 0 . 285 13 Feb 1981 7G 1 .218 0 . 382 14 Feb 1981 70 1 .973 0 . 984 T o t a l 388 1 . .761 0 . 595 Table 4.4 - G/R r a t i o s f o r 5 days of r a i n f a l l data range i n reported Z-R r e l a t i o n s h i p s and the v a r i a b l e nature of the drop s i z e d i s t r i b u t i o n . " The c o e f f i c i e n t of v a r i a t i o n f o r the f i v e day p e r i o d was s i x t y percent, which compares favourably w i t h the s i x t y - t h r e e percent observed by Wilson and Brandes, who go on to s t a t e that "much of the radar e r r o r r e s u l t s from storm-to-storm d i f f e r e n c e s i n the r e l a t i o n s h i p between rada r - r e c e i v e d power and r a i n f a l l r a t e " [ W i l s 7 9 ] . By removing the mean storm b i a s ( m u l t i p l y i n g the radar values by the average gauge to radar r a t i o f o r the storm) they reduced t h e i r e r r o r ( c o e f f i c i e n t of v a r i a t i o n ) to twenty-four percent. Humphries and Barge [Hump79a] observed gauge to radar r a t i o s of 1.1 and 1.3 f o r periods between f i v e and 420 minutes during two summer's operation of a ten cm radar i n A l b e r t a . Although t h e i r c o e f f i c i e n t s of v a r i a t i o n were q u i t e high (230 and 240 p e r c e n t ) , they reported that "accumulations over a point f o r long periods of time (1-2 months) can be accepted with a high degree of confidence without using a c a l i b r a t i o n raingauge t o adjust the radar measurements." Using c a l i b r a t e d radar v a l u e s , they found a s u b s t a n t i a l increase i n the e r r o r of the radar estimates with i n c r e a s i n g range - from f i f t e e n 60 percent at f i f t y km to ei g h t y percent at 120km, with r a t i o s at greater d i s t a n c e s showing a considerable underestimation of the p o i n t v a l u e s . The c o r r e l a t i o n of the gauge/radar r a t i o s w i t h d i s t a n c e i n t h i s study showed that there was a trend towards i n c r e a s i n g r a t i o with d i s t a n c e ( f i g . 4.15) but G A U G E / R A D A R RATIO C O R R E L A T E D WITH DISTANCE O "! i . i 9 or in < or < < O < ~ I I 1 1 1 1 1 1 1 r— NUMBER OF OBSERVATIONS = 388 CORRELATION COEFFICIENT = 0.135 L STANDARD ERROR OF ESTIMATE = 1.037 ~i r ~i 1 1 r J L W W 6.0 310 47.0 63.0 79.0 95.0 1110 127.0 143.0 DISTANCE FROM THE RADAR SITE (KM) 159.0 175.0 Figure 4.15 - G/R r a t i o as a f u n c t i o n of di s t a n c e from the radar although the radar underestimated r a i n f a l l to a greater degree f u r t h e r from the radar s i t e , no increase i n the e r r o r was observed. Other s t u d i e s have shown s i m i l a r r e s u l t s . A u s t i n 61 [Aust80a] found t h a t by using " j u d i c i o u s " raingauge c a l i b r a t i o n , a ccuracies on the order of t h i r t y percent could be expected f o r one. hour accumulations, while Huff e t . a l . [Huff80] and Vogel [Voge80] observed that under r e a l time o p e r a t i o n a l c o n d i t i o n s , twenty percent was the best e r r o r that could be achieved. The e r r o r f i g u r e s given have a l l been based on the assumption that the raingauge data was accurate, but the gauge measurements themselves may be i n e r r o r . Both A u s t i n and Wilson and Brandes note that the raingauge estimates of a r e a l r a i n f a l l are accurate to w i t h i n about f i v e percent f o r widespread, long-duration r a i n , but may be g r o s s l y i n e r r o r f o r convective showers - A u s t i n makes mention of a storm which caused s i g n i f i c a n t f l o o d i n g i n Ottawa but which d i d not pass over any of the gauges i n the c i t y . " I f there are s i g n i f i c a n t s p a t i a l g radients i n the accumulated amounts then i t i s p o s s i b l e that the radar b e t t e r represents the accumulation over that area than the point gauge measurement. Thus i t i s not c l e a r that a l l the e r r o r normally a t t r i b u t e d to the radar should be so placed f o r h y d r o l o g i c a l purposes" [Aust80a]. There are many p o s s i b l e causes of the di s c r e p a n c i e s between radar and raingauge measurements. R e f l e c t i v i t y v a r i a t i o n s , a t t e n u a t i o n of the beam, and changing beam e l e v a t i o n w i t h distance from the radar s i t e have been discussed p r e v i o u s l y . In a d d i t i o n to unrepresentative gauge sampling, A u s t i n [Aust80b] p o i n t s out that the method of time 62 i n t e g r a t i o n of the radar data may be important: the time i n t e g r a t i o n w i l l be i n e r r o r i f the time r e q u i r e d f o r intense echos to move from one g r i d point to an adjacent p o i n t i s l e s s that the i n t e g r a t i o n i n t e r v a l , as was the case w i t h the data in^ t h i s study. These f a c t o r s must be considered when radar-d e r i v e d s p a t i a l l y - b a s e d p r e c i p i t a t i o n data i s used i n engineering h y d r o l o g i c a l a p p l i c a t i o n s . 4.6 I n t e r a c t i v e Image D i s p l a y System The fourteen days of radar data received contained a vast amount of i n f o r m a t i o n . Each CAPPI g r i d c o n s i s t e d of over 45 000 p r e c i p i t a t i o n i n t e n s i t y measurements, y i e l d i n g a t o t a l of more than ninety-one m i l l i o n i n d i v i d u a l values f o r the 337 hours of records. For p r a c t i c a l a p p l i c a t i o n s i n engineering hydrology t h i s enormous amount of information had to be reduced and presented i n such a manner that i t could be e a s i l y and meaningfully a s s i m i l a t e d . The f i r s t step i n the reduction i n v o l v e d the choice of a subset of the radar coverage area. A 180 x 140 km region around the radar bounded by approximately 121° 30' and 124° longitude and 48° 20' and 49° 30' l a t i t u d e was chosen because i t i n c luded the metropolitan Vancouver and V i c t o r i a areas and excluded most of the occluded p o r t i o n s of the CAPPI measurement area. This reduced by a f a c t o r of seven the amount of data which had to be processed while r e t a i n i n g the s a l i e n t f e a t u r e s of the images. 63 P r e s e n t a t i o n of the data i n a manner such that there was a lar g e throughput of information while the important features were s t i l l e a s i l y d i s t i n g u i s h a b l e was the next c o n s i d e r a t i o n . Since humans have a "well-developed two- and three-d i m e n s i o n a l l y o r i e n t e d eye-brain p a t t e r n r e c o g n i t i o n mechanism which a l l o w s us to perceive and process many types of data very r a p i d l y and e f f i c i e n t l y i f the data are presented p i c t o r i a l l y " [Fole82], some form of a g r a p h i c a l r e p r e s e n t a t i o n of the information was the obvious choice. . Several a l t e r n a t i v e p i c t o r i a l formats were p o s s i b l e . The simplest method in v o l v e d s u b s t i t u t i n g a d i f f e r e n t character f o r each r a i n f a l l i n t e n s i t y to produce a character matrix image ( f i g . 4.16). This procedure i s very inexpensive, produces an unambiguous i n t e r p r e t a t i o n , and all o w s values to be measured from the image very e a s i l y . However, the p i x e l key i s awkward to use, p a t t e r n r e c o g n i t i o n i s d i f f i c u l t because many of the p i x e l characters are s i m i l a r , and the image i s not very a e s t h e t i c a l l y p l e a s i n g . The second a l t e r n a t i v e was i s o h y e t a l maps ( f i g . 4.17). Although t h i s r e p r e s e n t a t i o n , which i s f a m i l i a r t o engineers, a l l o w s values to be i n t e r p o l a t e d from the map, the steep gradients and r e c t i l i n e a r coordinates of the radar data often produce unusual contours which are d i f f i c u l t to i n t e r p r e t , and pa t t e r n s can be d i f f i c u l t t o f o l l o w from image t o image. This method of pr e s e n t a t i o n a l s o obscures the e s s e n t i a l l y matrix format of the data. P r e s e n t a t i o n of the r a i n f a l l data as a 64 Figure 4.16 - Character matrix r e p r e s e n t a t i o n of the r a i n f a l l p a t t e r n s 65 1934GMT 80/12/20 1944GMT 80/12/20 1954GMT 80/12/20 Figure 4.17 - I s o h y e t a l r e p r e s e n t a t i o n of the r a i n f a l l p a t t e r n s 66 three-dimensional surface was another option ( f i g . 4.18). In t h i s format patterns are r e l a t i v e l y easy to d i s t i n g u i s h and f o l l o w through s e q u e n t i a l images, but measurements from the p i c t u r e are impossible. The l a s t a l t e r n a t i v e considered was a col o u r image ( f i g . 4 . 1 9 ) . This has an advantage over the previous two options because l e s s processing of the data i s r e q u i r e d , w h i l e , given a s u f f i c i e n t l y l a r g e c o l o u r p a l e t t e , an unambiguous image can be obtained on which p a t t e r n s are e a s i l y recognized and from which measurements may be r e a d i l y made. The c o l o u r p i c t o r i a l r e p r e s e n t a t i o n was chosen as the primary method of pr e s e n t a t i o n f o r the radar-derived r a i n f a l l p atterns i n t h i s study. The amount and format of the data n e c e s s i t a t e d some type of computer processing system. A v a r i e t y of op t i o n s , i n c l u d i n g a graphics t e r m i n a l on a l a r g e m u l t i - u s e r computer, a powerful dedicated image a n a l y s i s system, and a microcomputer were considered. A microcomputer with colour graphics c a p a b i l i t y was chosen f o r the f o l l o w i n g reasons: 1. a v a i l a b i l i t y and low c o s t : a complete system, i n c l u d i n g d i s k storage, colour monitor, communications i n t e r f a c e , and software could be purchased o f f the s h e l f f o r about 6000 d o l l a r s , and the techniques and software developed here could e a s i l y be t r a n s f e r r e d elsewhere and placed i n t o immediate o p e r a t i o n ; 2. f l e x i b i l i t y : a microcomputer could be programmed to analyze and modify the images as w e l l as d i s p l a y them; 3. ease of programming: microcomputer software i s g e n e r a l l y Figure 4.18 - Hyetal surface r e p r e s e n t a t i o n of the r a i n f a l l p a t t e r n s F i g u r e 4 . 1 9 - C o l o u r r e p r e s e n t a t i o n o f t h e r a i n f a l l p a t t e r n s 69 w r i t t e n i n BASIC - an easy to l e a r n , i n t e r a c t i v e langauge wi t h b u i l t i n s c i e n t i f i c f u n c t i o n s and h i g h e r - l e v e l langauge c o n s t r u c t s ; 4. dedicated use: time- or use-sharing systems impose cost and time c o n s t r a i n t s on the a v a i l a b i l i t y of the computer, p a r t i c u l a r l y where r e a l - t i m e processing of images i s contemplated, but t h i s i s not the case with a microcomputer. However, the choice of a microcomputer was not without i t s disadvantages. Probably the most important drawback was processing speed: the small microprocessor word s i z e (eight or s i x t e e n b i t s ) and narrow data path width ( g e n e r a l l y e i g h t b i t s ) combined with the repeated reprocessing of statements by the BASIC i n t e r p r e t e r make microcomputer "number-crunching" p a i n f u l l y slow. The performance can be improved by recoding i n t o assembly langauge those segments which consume the gre a t e s t number of machine c y c l e s , but t h i s decreases the ease with which program m o d i f i c a t i o n s can be made and req u i r e s the programmer to have a much greater in-depth knowledge of the computer system. Most engineers are not prepared to invest the amount of time r e q u i r e d to gain t h i s knowledge, but as the requirements of most users of the radar data would be very s i m i l a r , standard software packages c o u l d be developed. A second disadvantage i s memory s i z e . Eight b i t processors have a memory a d d r e s s a b i l i t y c o n s t r a i n t of 64K bytes, which r e s t r i c t s the s i z e of programs which can be loaded and executed without swapping. The newer s i x t e e n b i t processors 70 overcome t h i s problem, and on these machines program s i z e i s not g e n e r a l l y a r e s t r i c t i o n . T h i s expenditure on a microcomputer system was e a s i l y j u s t i f i e d i n view of the amount of p r e c i p i t a t i o n information which c o u l d be accessed. A number of microcomputer systems were considered before the d e c i s i o n was made to purchase an IBM Personal Computer. The IBM was picked because i t had a s u p e r i o r processor a r c h i t e c t u r e ( s i x t e e n b i t word s i z e , 1 000 000 byte a d d r e s s a b i l i t y ) , higher r e s o l u t i o n graphics d i s p l a y c a p a b i l i t y , and b e t t e r documentation than any of the other systems a v a i l a b l e at the time f o r about the same c o s t . As set up t o d i s p l a y the CAPPI images, the computer was c o n f i g u r e d as: IBM PC (8088 processor) w i t h 40 K bytes ROM and 128 K bytes RAM 2 - 5 1/4" floppy d i s k d r i v e s w i t h 160K storage c a p a c i t y per d r i v e RS-232 s e r i a l communications i n t e r f a c e Amdek RGB colour monitor. This equipment was set up i n a l a b o r a t o r y i n the C i v i l Engineering b u i l d i n g ( f i g . 4.20). Software provided by IBM included the d i s k operating system, a BASIC i n t e r p r e t e r , and an 8086 assembler. The image d i s p l a y and a n a l y s i s programs were w r i t t e n i n BASIC. To t r a n s f e r the CAPPI data onto the microcomputer d i s k e t t e s i t was necessary to e s t a b l i s h a l i n k to a computer equipped wi t h 9-track tape d r i v e s . The U n i v e r s i t y of B r i t i s h 71 Figure 4.20 - IBM Personal Computer used for displaying the CAPPI images Columbia multi-user MTS system was used to read the tapes provided by AES and transmit the information to the microcomputer. To save time, the mainframe was also used to select the working portion of the g r i d , apply corrections, and convert the DVIP values to r a i n f a l l i n t e n s i t i e s , but these procedures could as e a s i l y have been implemented on the microcomputer. A s e r i a l communications l i n k with the UBC computer was i n s t a l l e d , and using software provided by a systems programmer at the Computing Centre, the CAPPI g r i d data was transferred to the microcomputer and stored on floppy disk ( f i g . 4 . 2 1 , appendix C). In a computer with a fixed colour display buffer si z e , a trade-off exists between the number of colours available and the resolution of the image. To obtain the screen resolution 72 Q_D 9-track tap* drlva dlak drlvaa Amdahl 470 IBM PC 0 o waInfrana • • r i a l communications 11nk microcomputer floppy dlak drlvaa Figure 4.21 - MTS host - IBM PC data t r a n s f e r l i n k necessary to d i s p l a y the 180 x 140 km region (320 x 200 p i x e l d i s p l a y mode), the number of co l o u r s p o s s i b l e was l i m i t e d to four. Thus only four p r e c i p i t a t i o n l e v e l s c ould be di s p l a y e d unambiguously. This could be increased by r e c y c l i n g the colour s c a l e f o r higher i n t e n s i t i e s , at the cost of making the image more d i f f i c u l t to i n t e r p r e t . This problem was solved by c r e a t i n g an eight colour d i s p l a y using the p r i n c i p l e of d i t h e r i n g . Since each p r e c i p i t a t i o n g r i d square was represented by four screen p i x e l s , i t was p o s s i b l e to simulate a new col o u r by mixing two of the basic c o l o u r s w i t h i n one g r i d square. Using t h i s process and a l i m i t e d c olour scale r e c y c l e , p r e c i p i t a t i o n images with an i n t e n s i t y r e s o l u t i o n of one mm/hr were produced. To a i d the i n t e r p r e t a t i o n , an o u t l i n e map of the area was overlayed on the screen ( f i g . 4.22). The north-south e l o n g a t i o n of the image i s due to the c l o s e r h o r i z o n t a l spacing of the screen p i x e l s . The microcomputer was programmed to provide a simple 73 A b b o t s f o r d SCEPTRE Radar L o c a t i on o f padai* & cone of s i l e n c e F i g u r e 4 .22 - C o l o u r m o n i t o r d i s p l a y s h o w i n g r a n g e r i n g s and o v e r l a y map i n t e r a c t i v e a n a l y s i s o f t h e p r e c i p i t a t i o n d a t a a s w e l l a s d i s p l a y i t . One u s e r - s e l e c t a b l e o p t i o n computed t h e t o t a l a r e a c o v e r e d by e a c h r a i n f a l l i n t e n s i t y l e v e l . From t h i s i n f o r m a t i o n t h e t o t a l d e p t h o f p r e c i p i t a t i o n r e c e i v e d d u r i n g e a c h measurement i n t e r v a l c o u l d e a s i l y be c a l c u l a t e d . A s e c o n d o p t i o n was programmed t o g e n e r a t e a h y e t o g r a p h f o r any l o c a t i o n w i t h i n t h e map a r e a . The u s e r s e l e c t e d t h e l o c a t i o n on t h e map by p o s i t i o n i n g a c u r s o r on t h e s c r e e n , and t h e h y e t o g r a p h was c o m p i l e d a s t h e images were d i s p l a y e d and t h e n p l o t t e d i n g r a p h f o r m . The amount o f r a i n f a l l a c c u m u l a t i o n o v e r t h e map a r e a f o r any p e r i o d c o u l d a l s o be computed and d i s p l a y e d . C o m b i n i n g s i m p l e i n t e r a c t i v e d a t a a n a l y s i s w i t h t h e image d i s p l a y c a p a b i l i t y y i e l d s a p o w e r f u l t o o l w h i c h a l l o w s e n g i n e e r s t o see t h e t y p e s o f r a i n f a l l p a t t e r n s w h i c h may be e x p e r i e n c e d d u r i n g s t o r m e v e n t s and a t t h e same t i m e observe how these r e l a t e t o the p o i n t hyetographs and r a i n f a l l accumulations normally used i n design c a l c u l a t i o n s . This i n t e r a c t i o n a i d s the development of an i n t u i t i v e f e e l f o r the r a i n f a l l data and promotes c o n s i d e r a t i o n of the s p a t i a l as w e l l as the temporal m u t a b i l i t y of p r e c i p i t a t i o n i n design p r a c t i c e . 4.7 Patterns of P r e c i p i t a t i o n over the Vancouver Area The p r e c i p i t a t i o n p a t t e r n s seen i n the 337 hours of radar data f o r the f i v e p a r t i a l storm records e x h i b i t e d the c h a r a c t e r i s t i c s t r u c t u r e s o u t l i n e d by Eagleson [Eagl70]. The area covered by the image precluded observation of any synoptic s c a l e p a t t e r n s . However, meso- and microscale s t r u c t u r e s were e a s i l y i d e n t i f i e d i n the p i c t u r e s . I t should be noted that the a c t u a l values measured on the images are probably too low by a f a c t o r of almost two. The causes of t h i s e r r o r , which v a r i e s i n both time and space, have already been o u t l i n e d i n previous s e c t i o n s . An e l l i p t i c a l area w i t h i n which no values are given i s included on the images (see the 1154Z image to gauge i t s extent) - t h i s corresponds to the c i r c u l a r cone of s i l e n c e around the radar s i t e . The sequence of images ( f i g . 4.23 to 4.37) from the December 1980 storm show the p r e c i p i t a t i o n r e s u l t i n g from an occluded f r o n t of a low pressure system passing over the Vancouver area. A "broad loose band" of p r e c i p i t a t i o n with a 75 . HX»XHJ t S l ^ u i u Radar 19 M i n u t e average r a i n f a l l intensity — . H H / h r 1 8 I 2 F i g u r e 4.23 - R a i n f a l l i n t e n s i t y p a t t e r n - 1044 GMT 22 December 1980 "V W aal • . ninute average r a i n f a l l intensity M M/hr F i g u r e 4.24 - R a i n f a l l i n t e n s i t y p a t t e r n - 1054 GMT 22 December 1980 " p e b b l y s t r u c t u r e " i s t h e most s t r i k i n g m e s o s c a l e f e a t u r e of t h e s e c y c l o n i c s t o r m s [ A u s t 5 9 ] a n d i s e a s i l y i d e n t i f i e d i n 76 F i g u r e 4.25 - R a i n f a l l i n t e n s i t y p a t t e r n - 1104 GMT 22 December 1980 F i g u r e 4.26 - R a i n f a l l i n t e n s i t y p a t t e r n - 1114 GMT 22 December 1980 t h i s s e q u e n c e . T h i s w e l l - d e f i n e d band moved i n an e a s t -n o r t h e a s t e r l y d i r e c t i o n , p e r p e n d i c u l a r t o t h e l i n e o f t h e 77 18 Minute average r a i n f a l l i n t e n s i t y | r ~ ' "—< 1 **/hr F i g u r e 4.27 - R a i n f a l l i n t e n s i t y p a t t e r n December 1980 - 1124 GMT 22 F i g u r e 4.28 - R a i n f a l l i n t e n s i t y p a t t e r n - 1134 GMT 22 December 1980 f r o n t , and t h e a v e r a g e p r e c i p i t a t i o n i n t e n s i t y i n t h e band i n c r e a s e d a s i t a p p r o a c h e d t h e m a i n l a n d c o a s t . The r a i n f a l l 78 F i g u r e 4.29 - R a i n f a l l i n t e n s i t y p a t t e r n - 1144 GMT 22 December 1980 F i g u r e 4.30 - R a i n f a l l i n t e n s i t y p a t t e r n - 1154 GMT 22 December 1980 a h e a d o f t h e f r o n t i s o r g a n i z e d i n t o i r r e g u l a r p a t c h e s a t t h e m e s o s c a l e l e v e l ( f i g 4.19) w h i c h move i n s t e p a s t h e c y c l o n i c 79 1 0 M i n u t e a v e r a g e r a i n f a l l i n t e n s i t y fcf « . * 7 1 MM/hr F i g u r e 4.31 - R a i n f a l l i n t e n s i t y p a t t e r n - 1204 GMT 22 December 1980 F i g u r e 4.32 - R a i n f a l l i n t e n s i t y p a t t e r n - 1214 GMT 22 December 1980 s y s t e m sweeps e a s t w a r d . Houze e t . a l . [Houz76] c l a s s i f i e d t h e r a i n f a l l bands f r o m P a c i f i c c y c l o n i c s t o r m s i n t o s i x 80 , • • J tm.»--» a i t • w, 1 0 M i n u t e a v e r a g e r a i n f a l l i n t e n s i t y Figure 4.34 - R a i n f a l l i n t e n s i t y p a t t e r n - 1234 GMT 22 December 1980 ca t e g o r i e s according to the type of f r o n t a s s o c i a t e d with the band. They noted that " i n some cases rainbands were 81 nju&nj V 3 i u m J \ , t r I JVC IVdltiajr 1 1 0 Minute a v e r a g e r a i n f a l l i n t e n s i t y --T - 7 ^ — T — J 1 «*/h* F i g u r e 4.35 - R a i n f a l l i n t e n s i t y p a t t e r n - 1244 GMT 22 December 1980 F i g u r e 4.36 - R a i n f a l l i n t e n s i t y p a t t e r n - 1254 GMT 22 December 1980 i n t e r s p e r s e d w i t h l a r g e r i r r e g u l a r l y s h a p e d r e g i o n s o f l i g h t r a i n , w h i l e i n o t h e r c a s e s s m a l l non-banded m e s o s c a l e r a i n 82 F i g u r e 4.37 - R a i n f a l l i n t e n s i t y p a t t e r n - 1304 GMT 22 December 1980 a r e a s o c c u r r e d between t h e b a n d s . " T h e i r f i n d i n g s were c o n f i r m e d i n t h i s s t u d y , where many non-banded m e s o s c a l e a r e a s were o b s e r v e d i n a d d i t i o n t o t h e wide c o l d - f r o n t a l r a i n b a n d s . The e f f e c t o f t h e m o u n t a i n o u s t o p o g r a p h y n o r t h o f t h e F r a s e r R i v e r i s a l s o c l e a r l y v i s i b l e i n t h i s s e q u e n c e o f i m a g e s . The band moves i n a c o h e r e n t f o r m u n t i l t h e n o r t h e r n end r e a c h e s t h e m o u n t a i n s n o r t h o f V a n c o u v e r , w h e r e a f t e r t h i s p o r t i o n i s r e t a r d e d r e l a t i v e t o t h e c e n t r a l p o r t i o n moving o v e r t h e f l a t F r a s e r R i v e r l o w l a n d s w h i c h c o n t i n u e d i t s g e n e r a l l y e a s t w a r d p r o g r e s s up t h e v a l l e y . The r e s u l t i s t h a t t h e a r e a n o r t h o f t h e F r a s e r R i v e r r e c e i v e s g r e a t e r p r e c i p i t a t i o n t h a n t h e l o w l a n d s due n o t o n l y t o t h e o r o g r a p h i c e f f e c t o f t h e m o u n t a i n s but a l s o due t o t h e r e t a r d a t i o n o f t h e f l o w w h i c h keeps t h e r a i n f a l l b e a r i n g a i r m a s s o v e r t h e a r e a 83 f o r a greater p e r i o d of time. This phenomenon i s p a r t i c u l a r l y obvious i n the l a t t e r h a l f of the image sequence. The p r e c i p i t a t i o n bands move in l a n d under the in f l u e n c e of the upper a i r flow. The v e l o c i t y of the system measured from t h i s sequence of images was f i f t y k i l ometres per hour, which was t y p i c a l of the v e l o c i t i e s observed f o r the other storms, a l l of which f e l l i n the t h i r t y to s i x t y - f i v e k ilometre per hour range of average f r o n t a l v e l o c i t i e s measured by Hobbs and Biswas [Hobb79] over Washington State. M i c r o s c a l e patterns can a l s o be d i s t i n g u i s h e d i n the images. The i n d i v i d u a l convective c e l l s ( g e n e r a l l y at the red or blue i n t e n s i t y l e v e l ) form w i t h i n the broad r a i n f a l l areas. Although other authors [Hobb79], [Aust59] have noted that the c e l l s move at a d i f f e r e n t v e l o c i t y to the general r a i n band, t h i s phenomenon was not observed i n the over 300 hours of storm records here: the convective c e l l s appeared to remain i n p o s i t i o n r e l a t i v e to the broad r a i n f a l l areas. By ta k i n g a lagrangian p e r s p e c t i v e , the temporal growth and decay of the i n d i v i d u a l c e l l s can be observed. The i n t e r v a l s during which the c e l l s remained i d e n t i f i a b l e ranged between t h i r t y and s i x t y minutes, which i s t y p i c a l of the durations found by other researchers [Aust59], [Eagl70], The peak i n t e n s i t y was u s u a l l y observed i n only one image, i n d i c a t i n g that the durat i o n of the maximum r a i n f a l l rate was ten minutes or sh o r t e r . Eagleson [Eagl70] has suggested that t h i s i n t e r v a l i s as short as a few minutes. 84 I t i s only by observing these patterns that one begins to ap p r e c i a t e the complexity inherent i n the p r e c i p i t a t i o n , a complexity not at a l l apparent from conventional hyetograph records. Current p r a c t i c e i s to analyze p o i n t r a i n f a l l data by" i g n o r i n g the movement of storms, assuming a s t a t i o n a r y growth and decay, or to consider a constant r a i n f a l l rate over an area f o r a c r i t i c a l time p e r i o d . An e x p l i c i t c o n s i d e r a t i o n of storm growth, v e l o c i t y , and track i s a p r e f e r a b l e approach, but t h i s r e q u i r e s knowledge of the s p a t i a l and temporal v a r i a t i o n of p r e c i p i t a t i o n . The Abbotsford SCEPTRE radar data a r c h i v e together with the data processing and v i s u a l d i s p l a y sofware developed here provide an economical and e a s i l y assimulated source of t h i s i n f o r m a t i o n . 85 CHAPTER V HYDROLOGICAL APPLICATIONS OF SCEPTRE RADAR DATA 5.1 I n t r o d u c t i o n P o t e n t i a l a p p l i c a t i o n s of SCEPTRE p r e c i p i t a t i o n data to engineering hydrology are discussed i n t h i s chapter. A f t e r o u t l i n i n g general uses of radar-derived r a i n f a l l i n f o r m a t i o n , the p o s s i b i l i t y of using SCEPTRE data as input to hydrologic runoff models i s i n v e s t i g a t e d . Both the b e n e f i t s and l i m i t a t i o n s of t h i s data source i n urban runoff modelling are demonstrated i n a case study of a Vancouver catchment simulated using the Storm Water Management Model. The chapter concludes w i t h recommendations f o r improvements to the SCEPTRE radar system and AES data a r c h i v e to provide higher q u a l i t y data and improved access f o r engineering h y d r o l o g i c a p p l i c a t i o n s . 5.2 General A p p l i c a t i o n s There are many p o t e n t i a l a p p l i c a t i o n s f o r comprehensive, s p a t i a l l y - r e f e r e n c e d p r e c i p i t a t i o n data. Radar, which i s the primary source of such data, was f i r s t adapted f o r p r e c i p i t a t i o n measurement i n the l a t e 1940's, but i t wasn't u n t i l the development of d i g i t a l systems i n the 1970's that i t s use i n engineering hydrology became f e a s i b l e . Moreover, only r e c e n t l y have attempts been made t o apply radar-derived 8 6 r a i n f a l l measurements to engineering problems, and the use of such data i s s t i l l f a r from r o u t i n e . Research i n t h i s area continues, and new a p p l i c a t i o n s w i l l be found as the r e l i a b i l i t y and accuracy of the radar systems i s improved and the u t i l i z a t i o n of radar-derived p r e c i p i t a t i o n records becomes accepted by the general engineering community. M e t e o r o l o g i c a l research i n t o the s t r u c t u r e of storms and the p h y s i c s of p r e c i p i t a t i o n was one of the f i r s t a p p l i c a t i o n s of weather radar, and continues to play an important r o l e . New techniques, such as the a p p l i c a t i o n of doppler radar to meteorology, have been developed at the research i n s t a l l a t i o n s , and the e x i s t i n g technology has been r e f i n e d using these s i t e s as prototypes f o r o p e r a t i o n a l systems. The l i t e r a t u r e contains many d e s c r i p t i o n s of t h i s research work, but most of i t i s too t h e o r e t i c a l to have immediate a p p l i c a t i o n i n engineering hydrology. C u r r e n t l y , the primary use of p r e c i p i t a t i o n - m e a s u r i n g radar i s f o r r a i n f a l l f o r e c a s t i n g . A network of ten cm WSR-57 radars has been e s t a b l i s h e d f o r t h i s purpose i n the United S t a t e s , while i n Canada, the d i g i t a l SCEPTRE system i s used p r i n c i p a l l y i n t h i s r o l e . S i m i l a r use i s made of weather radar i n s e v e r a l other c o u n t r i e s ( B r a z i l and Great B r i t a i n both operate such equipment). Sauvageau [ S a u v 8 l ] gives an overview of a l l of the p r e c i p i t a t i o n f o r e c a s t i n g systems c u r r e n t l y i n operation i n Canada. One of the a p p l i c a t i o n s of radar r a i n f a l l measurements 87 which has engineering s i g n i f i c a n c e i s streamflow p r e d i c t i o n and f l a s h f l o o d warning. This u t i l i z e s the radar data as input to a runaff model to generate streamflow p r e d i c t i o n s i n r e a l - t i m e . A runoff model capable of making use of the s p a t i a l l y d i s t r i b u t e d p r e c i p i t a t i o n input data i s required i n t h i s s i t u a t i o n . Koren [Kore78] d e s c r i b e s an implementation of f l a s h f l o o d p r e d i c t i o n i n the S o v i e t Union. In the United S t a t e s , S a f f l e and Greene [Saff78] i l l u s t r a t e another approach w i t h a case study using the D/RADEX d i g i t a l radar system. A p p l i c a t i o n of radar data to q u a l i t a t i v e streamflow f o r e c a s t i n g i n A l b e r t a was demonstrated by Humphries and Barge [Hump79b], who computed d a i l y r a i n f a l l maps f o r remote headwaters to enable h y d r o l o g i s t s to p r e d i c t streamflows downstream i n more populated areas. Radar-derived p r e c i p t i a t i o n data has been u t i l i z e d i n the r e a l - t i m e c o n t r o l of r e s e r v o i r s and storm sewer systems. Recent work by Huff, Towery, Vogel, and others [Huff78], [Voge80], [Huff80] of the I l l i n o i s State Water Survey has demonstrated the v i a b i l i t y of r e a l - t i m e radar data used i n c o n j u n c t i o n w i t h telemetered raingauge measurements as data input t o an urban water c o n t r o l system. The complexity of the Chicago sewer and storm drainage system demands some form of automated c o n t r o l , and t h i s i n turn r e q u i r e s access to p r e c i p i t a t i o n data i n r e a l - t i m e . Two weather radars and a dense raingauge network are being used to study the time-space c h a r a c t e r i s t i c s of storms and f o r e c a s t a r e a l r a i n f a l l i n the m e t r o p o l i t a n Chicago area. James and Robinson [Jame8l] have 88 proposed a s i m i l a r system f o r the Hamilton area. In t h e i r study, the monitoring of both the q u a l i t y and q u a n t i t y of the runoff was of concern, They proposed to minimize p o l l u t a n t loadings on the Hamilton r e c e i v i n g waters by using a re a l - t i m e c o n t r o l system based on a n a l y s i s using the Storm Water Management Model (SWMM). Although the use of c a l i b r a t e d radar data i s not s p e c i f i c a l l y mentioned i n the propo s a l , a s u i t a b l e radar system would be a p r a c t i c a l a l t e r n a t i v e to the telemetered raingauge network that was suggested. The r e a l -time urban runoff management techniques o u t l i n e d above r e q u i r e accurate, comprehensive, and time l y p r e c i p i t a t i o n data, and a c a l i b r a t e d weather radar i s a v i a b l e source of such i n f o r m a t i o n . Automated r e a l - t i m e f o r e c a s t i n g of r a i n f a l l r e q u i r e s the r e c o g n i t i o n and e x t r a p o l a t i o n of p r e c i p i t a t i o n p a t t e r n s . Some researchers have been working to develop c e l l i d e n t i f i c a t i o n and t r a c k i n g a l gorithms. Blackmer and Duda [Blac72], w e l l -known authors i n the p a t t e r n r e c o g n i t i o n f i e l d , used c l u s t e r i n g techniques to d e l i m i t radar echoes and l o c a l c o r r e l a t i o n procedures f o r echo t r a c k i n g . In the work of Brady, e t . a l . [Brad78], echoes were grouped i n t o complexes and tracked by simple c o r r e l a t i o n techniques. Neither of these papers demonstrated completely accurate and fool p r o o f methods f o r re c o g n i z i n g and t r a c k i n g storm c e l l s : more research i s needed i n t h i s area before automated r e a l - t i m e drainage c o n t r o l systems such as that envisaged f o r Chicago can be s u c c e s s f u l l y implemented. 89 From an engineering hydrology p e r s p e c t i v e , one of the most promising a p p l i c a t i o n s of p r e c i p i t a t i o n - m e a s u r i n g radar i s i n the study of r a i n f a l l p a t terns w i t h a view t o determining a more r e a l i s t i c r e p r e s e n t a t i o n of the design storm. "The v e r i f i c a t i o n of the suggestion, due to J.S. M a r s h a l l , that a few hours of radar data c o n t a i n i n a re p r e s e n t a t i v e way the var i o u s kinds of convective p r e c i p i t a t i o n that can occur i n a l o c a l i t y over a l a r g e period of time" [Druf76] means that extreme l o c a l events may be synthesized from a study of a much shorter complete a r e a l records. As was described i n a previous chapter, convective r a i n f a l l c e l l s grow and decay as they move. In the context of urban r u n o f f , the design r a i n f a l l i n t e n s i t y i s u s u a l l y due t o a s i n g l e c e l l t r a c k i n g d i r e c t l y over a basin while simultaneaously reaching i t s peak r a i n f a l l r a t e . The i d e n t i f i c a t i o n of c e l l growth and movement i s impossible except from a s p a t i a l d e s c r i p t i o n of the p r e c i p i t a t i o n , which r e q u i r e s a very l a r g e , dense gauge network or a weather radar. Hence the study of storm c e l l p a t t e r n s from radar r a i n f a l l images i s an i d e a l approach to develop b e t t e r design storm parameters which encompass the v a r i a b l i l i t y of c e l l s i z e , shape, growth r a t e , spacing, v e l o c i t y , and t r a c k . Konrad [Konr78] g i v e s a survey of attempts t o desc r i b e s t a t i s t i c a l l y the c h a r a c t e r i s t i c s of p r e c i p i t a t i o n c e l l s and develops h i s own a n a l y s i s f o r convective rainshowers. However, the values of these parameters vary from region to re g i o n , thus although 90 analyses have been undertaken for several areas of the United States and Canada, a study which takes into consideration the factors influencing p r e c i p i t a t i o n in the Vancouver area using l o c a l data i s necessary to determine design storm parameters for t h i s region. 5.3 Application to Engineering Hydrology - Runoff Modelling The p o t e n t i a l of radar-derived p r e c i p i t a t i o n data in engineering hydrology applications has not yet been f u l l y r e a l i z e d . As a data source in runoff simulation, s p a t i a l l y referenced radar measurements of f e r some d i s t i n c t advantages over t r a d i t i o n a l point raingauge records. However, t h i s r e l a t i v e l y new tool i s not without i t s l i m i t a t i o n s , and the s p e c i f i c application w i l l determine the degree of a p p l i c a b i l i t y of radar-derived r a i n f a l l data. These strengths and weaknesses are discussed here. From the viewpoint of data c o l l e c t i o n and management, radar measurement of r a i n f a l l i s a very a t t r a c t i v e a l t e r n a t i v e . Given the high cost of i n s t a l l i n g and operating a dense network of telemetered or recording raingauges, the c e n t r a l l i z e d measurement f a c i l i t y of the radar system may be s i g n i f i c a n t l y cheaper o v e r a l l . This advantage i s p a r t i c u l a r l y important where real-time processing of the data i s required, but even in the non-telemetered gauge s i t u a t i o n the radar eliminates the need for the time consuming and labour intensive e f f o r t of compiling and entering the gauge data -91 computer c o n t r o l l e d d i g i t a l r a d a r systems g e n e r a t e r e c o r d s i n an o r g a n i z e d , machine r e a d a b l e f o r m a t . I n a d d i t i o n , r a d a r measurements o b v i a t e t h e n e c e s s i t y of c o n s i d e r i n g c/auge s i t i n g f a c t o r s , such as exposure and e l e v a t i o n , when u s i n g the d a t a . The s p a t i a l and t e m p o r a l measurement c h a r a c t e r i s t i c s a r e a n o t h e r f o r t e of r a d a r - d e r i v e d r a i n f a l l d a t a . Because r a d a r measurements a r e made i n the atmosphere, independent of s u r f a c e f e a t u r e s , l a n d use, and v e g e t a t i o n , r e a d i n g s may be o b t a i n e d f o r a r e a s f o r which r a i n g a u g e measurements would be i m p r a c t i c a l , such as over l a k e s , dense f o r e s t s , e t c . In a d d i t i o n , the r a d a r d a t a g r i d i s e v e n l y spaced over the whole r e g i o n , e l i m i n a t i n g t h e problems of a r e a l b i a s i n r e c o r d s , and hence i n any s i m u l a t i o n c a r r i e d out u s i n g the d a t a , due t o n o n - u n i f o r m i t i e s i n the d i s t r i b u t i o n of gauge l o c a t i o n s . T e m p o r a l l y , r a d a r measurements may be o b t a i n e d f o r as s h o r t or s h o r t e r p e r i o d s than gauge v a l u e s . Time i n t e r v a l s between s u c c e s s i v e r e c o r d s of f i v e or t e n minutes a r e t y p i c a l , d epending on the s a m p l i n g regime implemented. As d i s c u s s e d i n t h e p r e v i o u s c h a p t e r , the a c c u r a c y of the r a d a r measurements i s one of t h e weak p o i n t s of t h i s d a t a s o u r c e . U s i n g one or two r a i n g a u g e s t o c a l i b r a t e the r a d a r , r e s u l t s w i t h an e r r o r of about t h i r t y p e r c e n t may be o b t a i n e d . I t was p o i n t e d out e a r l i e r t h a t t h i s e r r o r d e c r e a s e s s i g n i f i c a n t l y w i t h i n c r e a s i n g l e n g t h of a c c u m u l a t i o n p e r i o d : t h u s the r a d a r r a i n f a l l d a t a may c u r r e n t l y be b e t t e r s u i t e d t o l o n g - t e r m , c o n t i n u o u s s i m u l a t i o n than t o s i n g l e event 92 modelling. When viewed as an o p e r a t i o n a l source of p r e c i p i t a t i o n data f o r engineering h y d r o l o g i c a l purposes,, the e x i s t i n g SCEPTRE radar has d i s t i n c t shortcomings. For use i n large f o r e c a s t i n g models, such as the UBC Watershed Model, the r e s o l u t i o n of the radar i s too f i n e : more data i s generated than i s of p r a c t i c a l use i n the s i m u l a t i o n . Although t h i s problem c o u l d be overcome by lumping the values i n t o a coarser g r i d , the l i m i t e d u s e f u l range of the system precludes the measurement of r a i n f a l l over a l l but a small p o r t i o n of the t o t a l area being modelled. Radar measurements are p a r t i c u l a r l y s u s c e p t i b l e to i n t e r f e r e n c e from topography, a very important c o n s i d e r a t i o n given the rugged t e r r a i n found i n B r i t i s h Columbia. In a d d i t i o n , the d i f f e r i n g r e f l e c t i v i t y c o e f f i c i e n t s f o r r a i n and snow make the use of radar much more d i f f i c u l t i n regions where both r a i n and snow occur. Thus the SCEPTRE radar could not be economically j u s t i f i e d s o l e l y on the b a s i s of p r o v i d i n g m e t e r o l o g i c a l data f o r l a r g e basin runoff m o d e l l i n g . In the context of urban runoff modelling, where the basin le n g t h i s oft e n smaller than the two km square g r i d spacing, the SCEPTRE radar provides a coarser s p a t i a l r e s o l u t i o n than would be i d e a l . At t h i s l e v e l of d e t a i l , h i g h - i n t e n s i t y convective p r e c i p i t a t i o n dominates as the design c r i t e r i a . Although the SCEPTRE radar data provides comprehensive s p a t i a l r a i n f a l l i nformation which i n c l u d e s measurements of i n t e n s i t y 93 i n the convective c e l l s , the r e s o l u t i o n i s not f i n e enough to show the e f f e c t of the d i r e c t i o n and v e l o c i t y of c e l l movement on the runoff from the b a s i n . Since the storm speed i s o f t e n on the order of f i f t y k ilometres per hour, a c e l l w i l l t r a v e l almost three g r i d squares i n the ten minutes between samples, and may pass over a small basin without being detected d i r e c t l y over i t . Thus the temporal r e s o l u t i o n of t h i s radar i s a l s o inadequate f o r most urban runoff modelling. Here again, the o p e r a t i o n a l SCEPTRE radar cannot be j u s t i f i e d s o l e l y on the b a s i s of being an engineering measurement t o o l . 5.4 Engineering use of Radar-Derived P r e c i p i t a t i o n Data: Urban  Runoff Case Study Despite the f a c t that the SCEPTRE radar system s u f f e r s from d e f i c i e n c i e s which l i m i t i t s usefulness as a source of s p a t i a l r a i n f a l l data f o r urban runoff modelling, the p r i n c i p l e of using r a d a r - d e r i v e d measurements i n runoff s i m u l a t i o n s i s sound. Since the c h a r a c t e r i s t i c s of the basin being modelled vary i n two-dimensions, the r a i n f a l l input should vary l i k e w i s e to o b t a i n accurate runoff values. Engineers experienced i n urban runoff modelling have advised that "even f o r small catchments, runoff and consequent model p r e d i c t i o n s may be very s e n s i t i v e to s p a t i a l v a r i a t i o n s i n r a i n f a l l " [Hube8l]. However, these same authors f a i l to recognize t h a t t h i s v a r i a b i l i t y extends t o f r o n t a l systems as w e l l when they s t a t e that " i f the r a i n f a l l i s uniform s p a t i a l l y , as might be expected from c y c l o n i c storms, these 94 s p a t i a l c o n s i d e r a t i o n s are not as important." To i n v e s t i g a t e the s e n s i t i v i t y pf an urban catchment to s p a t i a l and temporal v a r i a t i o n s i n r a i n f a l l , a catchment i n the F a i r v i e w area of southeast Vancouver was modelled with the Storm Water Management Model using the Abbotsford SCEPTRE radar data as p r e c i p i t a t i o n input. The catchment i s a r e l a t i v e l y new s u b d i v i s i o n with separate storm and s a n i t a r y sewers (much of Vancouver i s on combined sewer systems). The long, narrow basin i s o r i e n t e d with the long a x i s approximately north-south, and d r a i n s i n t o the Fraser River at the south end ( f i g . 5.1). The basin was d i s c r e t i z e d i n t o twelve subcatchments. Standard i n f i l t r a t i o n and roughness c o e f f i c i e n t s were adopted f o r the s i m u l a t i o n [SWMM76]. The runoff block of the model was used to c a l c u l a t e an o u t l e t hydrograph at the Fraser River o u t f a l l . No q u a l i t y modelling was i n c l u d e d . P r e c i p i t a t i o n data input was taken from the Abbotsford SCEPTRE radar for the December 1980 storm event. The catchment spanned two radar measurement g r i d squares: the three most n o r t h e r l y subcatchments i n one square and the remainder i n an adjacent one. Input hyetographs for the subcatchments were taken as the values f o r the radar g r i d squares i n which they were s i t u a t e d . The model time increment was taken as the same value as the i n t e r v a l between p r e c i p i t a t i o n measurements: ten minutes. The o u t l e t hydrograph ( f i g . 5.2) i s i n d i c a t i v e of a basin with a 95 Figure 5.1 - Map of Fraserview catchment r e l a t i v e l y f a s t response time - i n t h i s case due to the comparatively steep slopes i n p o r t i o n s of the b a s i n . To determine the s p a t i a l s e n s i t i v i t y of the b a s i n , the s i m u l a t i o n was repeated w i t h the storm d i r e c t i o n reversed. A comparison of the r e s u l t i n g hydrographs ( f i g . 5.3) shows only minor d i f f e r e n c e s . S i m i l a r r e s u l t s were obtained when the storm t r a c k was s h i f t e d two kilometres east and west of i t s a c t u a l t r a c k . This a n a l y s i s seems to imply that storm d i r e c t i o n and path are not very c r i t i c a l f a c t o r s i n runoff 96 FRASERVIEW CATCHMENT OUTLET HYDROGRAPH e> •- .. ** I i i i 1 1 1 1 — - i 1 1 1 1 1 1 1 1 1 1 r 0.0 20.0 40.0 60.0 80.0 100.0 120.0 U0.O 160.0 1B0.O 200.0 TIME (MINUTES) (X101 ) . Figure 5.2 - SWMM o u t l e t hydrograph f o r the Fraserview catchment, December 1980 storm modelling, and hence i n storm sewer design. This i s somewhat contr a r y to what was expected from a study of the p r e c i p i t a t i o n p a tterns themselves. This lack of s e n s i s t i v i t y may i n part be due to the s p a t i a l r e s o l u t i o n l i m i t a t i o n s of the radar - sin c e most of the basin l i e s w i t h i n one radar g r i d square, the model places the same r a i n f a l l over the most of the basin area at the same time, and thus the e f f e c t s of storm motion are not seen. Therefore the r e s u l t s may best be 97 F R A S E R V I E W C A T C H M E N T O U T L E T H Y D R O G R A P H o -9 L "I I I I I I I I 1 1 1 1 1 1 1 1 1 1 r-CORRECT DIRECTION REVERSED DIRECTION Aj. i 1 0.0 7C.0 «C.O 60.0 80.0 lOOJO 120.0 UO 0 TIME (MINUTES) (X10 1 ) 16C.C 180.0 700.0 F i g u r e 5 . 3 - Comparison of SWMM o u t l e t hydrographs f o r normal and reversed storm d i r e c t i o n s d e scribed as i n c o n c l u s i v e as f a r as demonstrating s p a t i a l s e n s i t i v i t y : higher s p a t i a l r e s o l u t i o n radar data i s needed before a general c o n c l u s i o n may be made. The temporal s e n s i t i v i t y of the model was demonstrated by app l y i n g equivalent hourly p r e c i p i t a t i o n data from the nearest r e c o r d i n g raingauge, nine kilometres away, to the same ba s i n . The t o t a l volume of t h i s r a i n f a l l was comparable to that 98 obtained from the radar. A comparison of the r e s u l t i n g hydrographs ( f i g . 5 . 4 ) c l e a r l y shows the inadequacy of the FRASERVIEW CATCHMENT OUTLET HYDROGRAPH 20.0 40.0 60.0 80.0 100.0 120.0 UO.O 160 0 180 C 70C 0 TIME (MINUTES) (X10 1 ) F i g u r e 5 .4 - Comparison of SWMM hydrographs from ten minute radar and equivalent hourly gauge data hourly data i n t h i s model. The peak runoff from the hourly data underestimates that from the radar data by a f a c t o r of thr e e , and although the timings of the other runoff peaks agree i n both hydrographs, a l l those from the hourly values 99 show lower flows. This dramatic d i f f e r e n c e i s l a r g e l y due to the averaging of the peak p r e c i p i t a t i o n i n t e n s i t i e s i n the hourly records, reducing the maximum values, which when input to the model, produce more i n f i l t r a t i o n and hence l e s s d i r e c t r u n o f f . As was noted e a r l i e r , r a i n f a l l accumulations derived from s p a t i a l p r e c i p i t a t i o n data by i n t e g r a t i n g p e r i o d i c measurements w i l l be g r o s s l y i n e r r o r i f the storm v e l o c i t y i s such that c e l l movement between samples i s greater than one g r i d spacing. This i s a l s o one f a c t o r i n determining the s u i t a b i l i t y of a data base of s p a t i a l p r e c i p i t a t i o n records to runoff modelling. S p a t i a l r e s o l u t i o n c r i t e r i a are a f u n c t i o n of the s i z e of the basin and the type of model employed. The necessary temporal r e s o l u t i o n i s e s t a b l i s h e d by the basin response time. But the combination of the two i s a l s o c r i t i c a l , and depends on the v e l o c i t y of the storm system. This r e l a t i o n s h i p may be seen i n the p l o t of the s p a t i a l versus temporal r e s o l u t i o n of r a i n f a l l data sources ( f i g . 5.5) The l i n e represents matching r e s o l u t i o n s under the storm v e l o c i t y c r i t e r i a . The basin s i z e and response time c r i t e r i a would be shown as h o r i z o n t a l and v e r t i c a l l i n e s r e s p e c t i v e l y . Thus the minimum s p a t i a l and temporal r e s o l u t i o n r e quired corresponds t o the i n t e r s e c t i o n of the diagonal l i n e w i t h the time or space c r i t e r i a l i n e s which l i e s c l o s e s t to the o r i g i n . A l t e r n a t i v e l y , given a source of s p a t i a l r a i n f a l l data with known r e s o l u t i o n l i m i t a t i o n s , the type of basin and model i t i s best s u i t e d f o r may be determined. As can be seen, the 100 S P A T I A L / T E M P O R A L RESOLUTION OF RAINFALL MEASUREMENTS 3 5 7 » • 3 5 7 10" 3 5 7 K>» 3 5 7 10* 3 5 7 KJ' TIME BETWEEN RECORDS (MINUTES) Figure 5.5 - Sp a t i a l / t e m p o r a l r e s o l u t i o n requirements of r a i n f a l l data - storm v e l o c i t y 60 kmh radar data l i e s below the l i n e , i n d i c a t i n g that temporal r e s o l u t i o n i s the c r i t i c a l d e f i c i e n c y . S i m i l a r l y , the d a i l y gauge data, when taken as a s p a t i a l network of observations, i s inadequate f o r modelling a l l but the l a r g e s t of basins. In an urban runoff modelling s i t u a t i o n , a s p a t i a l c r i t e r i a of h a l f a kilometre r e s o l u t i o n would then a l s o r e q u i r e t h i r t y second temporal r e s o l u t i o n . Coordinated measurements on t h i s time s c a l e would be d i f f i c u l t to obtain from raingauges, but a 101 radar system dedicated to high r e s o l u t i o n measurement over an urban area c o u l d f u l f i l l these requirements. The i n c r e a s i n g cost of water resource systems i s f o r c i n g engineers t o undertake more extensive analyses using more complicated modelling procedures to avoid expensive overdesign p r a c t i c e s . These complex models r e q u i r e an extensive h i s t o r i c a l p r e c i p i t a t i o n data base, or a r e a l i s t i c design storm which takes i n t o account the e f f e c t s of l o c a l phenomena, to produce v i a b l e r e s u l t s . The e x i s t i n g p r e c i p i t a t i o n gauge network i s inadequate f o r t h i s purpose, and the SCEPTRE radar, while a d i s t i n c t improvement i n s p a t i a l and temporal r e s o l u t i o n over the poin t gauge data, has drawbacks which l i m i t i t s usefulness as a source of engineering p r e c i p t i a t i o n data. 5.5 Recommendations f o r Improvements to the SCEPTRE Radar and  Data Archive and R e t r i e v a l There are a number of improvements which would be r e l a t i v e l y easy to implement on the SCEPTRE radar to allow more widespread access to the data i t provides. Given the la r g e c a p i t a l investment and maintenance c o s t s f o r such a f a c i l i t y , more use of the data would provide a greater r e t u r n on the investment and j u s t i f y the c o n t i n u a t i o n of the data a r c h i v e . The c u r r e n t p r a c t i c e of mai n t a i n i n g a complete a r c h i v e of p r e c i p i t a t i o n data may have to be abandoned i n favour of a 102 procedure which saves only s i g n i f i c a n t storm events. C e r t a i n l y , the vast m a j o r i t y of engineering hydrology a p p l i c a t i o n s r e q u i r e only data f o r major storms, not a complete record. The reduction i n the amount of data to be a r c h i v e d would allow more money and e f f o r t t o be spent on processing and a n a l y s i s of the important records, y i e l d i n g i n f o r m a t i o n of much more value t o the engineering community than i s c u r r e n t l y provided by the complete radar data a r c h i v e . There are s e v e r a l ways i n which the r e a l - t i m e r a i n f a l l i n formation could be made a v a i l a b l e to the p u b l i c which would r e q u i r e very l i t t l e equipment or software to be added to the system. The f i r s t i s to i n s t a l l a low speed, s e r i a l communication d i a l - u p f a c i l i t y to a l l o w a user w i t h a computer and a modem connection to obtain d i g i t a l r a i n f a l l i n t e n s i t i e s and accumulations f o r a region around the radar s i m i l a r i n extent to that chosen i n t h i s study. For example, by choosing a subset of the coverage region which contains most of the populous area of southwestern B r i t i s h Columbia while excluding most of the areas occluded by mountains, one complete image data-set could t r a n s m i t t e d i n about three minutes at 300 baud. The a v a i l a b i l i t y of s m a l l , inexpensive computer systems w i t h communications i n t e r f a c e c a p a b i l i t y makes t h i s p r a c t i c a l f o r a wide v a r i e t y of users of p r e c i p i t a t i o n data. Such a s e r v i c e would be of great use t o many companies and government agencies i n the area, such as those operating r e s e r v o i r s , storm sewer c o n t r o l f a c i l i t i e s , and sewage treatment p l a n t s , to a l l o w them to make d e c i s i o n s based on general or l o c a l 103 a c c u r a t e , up-to-date information rather than based ' on estimates from l o c a l weather f o r e c a s t s . In a s i m i l a r v e i n , the new Telidon i n t e r a c t i v e information r e t r i e v a l system o f f e r s the opportunity to provide these radar r a i n f a l l p a t t e r n s to a wide range of people at a very low c o s t . The Te l i d o n data base could be updated w i t h a new colour p r e c i p i t a t i o n map on an hourly b a s i s . This i n f o r m a t i o n could be of un t o l d use to many small businessmen, farmers, e t c . who would then have access to more r e a l i s t i c short-term r a i n f a l l i n f o r m a t i o n . The returns to the community would amply repay the modest investment i n v o l v e d , and provide j u s t i f i c a t i o n f or the continued operation and improvement of the system. Before wider use and acceptance of the radar-derived r a i n f a l l information i s p o s s i b l e , enhancements to the SCEPTRE data processing software are necessary. The a d d i t i o n of moving t a r g e t i n d i c a t o r processing would remove the spurious r a i n f a l l values caused by echos o f f nearby mountains and e l i m i n a t e the need f o r the overlay mask. These d e t r a c t from the image pres e n t a t i o n and obscure some areas w i t h i n which v a l i d measurments are p o s s i b l e . A second requirement i s that the images be free of r i n g a r t i f a c t s caused during CAPPI c o n s t r u c t i o n . Again, by enhancing the e x i s t i n g software i t should be p o s s i b l e t o e l i m i n a t e t h i s e r r o r source. Many small engineering c o n s u l t a n t s do not have access to a computer supporting a 9-track tape d r i v e , which i s c u r r e n t l y a p r e r e q u i s i t e to reading AES su p p l i e d magnetic tapes. These 104 companies of t e n do own or would be w i l l i n g to purchase a small minicomputer or microcomputer, which uses floppy d i s k s f o r mass storage. As a s e r v i c e to the engineering community, which o f t e n makes p r a c t i c a l use of h i s t o r i c p r e c i p i t a t i o n data, AES should consider making both radar and raingauge r a i n f a l l h i s t o r i c data a v a i l a b l e on t h i s medium as an a l t e r n a t i v e to the more expensive and l e s s e a s i l y accessed magnetic tapes. Using a standard format on widely accepted operating systems such as CPM, UNIX, e t c . , t h i s s e r v i c e would g r e a t l y enhance a c c e s s i b i l i t y to the data f o r a minimal increased cost to AES. By adding a small amount of e x t r a c a p a b i l i t y to the SCEPTRE system, a r c h i v i n g only s i g n i f i c a n t storm events, and p r o v i d i n g p r e c i p i t a t i o n data on more widely useable medium i n standard formats, AES can v a s t l y improve the access to t h e i r m e t e o r o l o g i c a l data. These improvements would be of great b e n e f i t to the engineering community, and i n d i r e c t l y to the p u b l i c , compounding the r e t u r n on investment from the m e t e o l o l o g i c a l d a t a - c o l l e c t i o n network f o r a minimal a d d i t i o n a l c o s t . 105 CHAPTER VI CONCLUSIONS The development of a n a l y t i c a l water resource models which r e q u i r e accurate and comprehensive p r e c i p i t a t i o n data has not been accompanied by appropriate improvements i n p r e c i p i t a t i o n data bases. Radar measurement of r a i n f a l l i s a method which o f f e r s the promise of p r o v i d i n g data w i t h the necessary s p a t i a l and temporal r e s o l u t i o n at a reasonable c o s t . The existe n c e of a major o p e r a t i o n a l radar system and data archive would n a t u r a l l y suggest the u s e f u l a p p l i c a t i o n of t h i s data. This study revealed t h a t , while i t has co n s i d e r a b l e p o t e n t i a l , the c a p a b i l i t i e s of the present SCEPTRE system do not properly meet engineering hydrology needs. However, some s i g n i f i c a n t b e n e f i t s are s t i l l a t t a i n a b l e . The s p a t i a l l y - r e f e r e n c e d SCEPTRE radar data provides new i n s i g h t i n t o the s t r u c t u r e and movement of p r e c i p i t a t i o n p a t t e r n s over the Vancouver area which i s p r e s e n t l y impossible to obtain from any other source. Some of the p o t e n t i a l b e n e f i t s of the SCEPTRE data were demonstrated when the radar imagery was presented i n a colour g r a p h i c a l format which allowed the vast q u a n t i t y of r a i n f a l l i n formation provided by the radar t o be e a s i l y a s s i m i l a t e d . The s e n s i t i v i t y of urban catchments to s p a t i a l and temporal v a r i a t i o n s i n p r e c i p i t a t i o n was i n v e s t i g a t e d by app l y i n g the radar data to an engineering runoff model. Time-space r e s o l u t i o n c r i t e r i a f o r s p a t i a l 106 p r e c i p i t a t i o n data employed i n water resources models were determined from an examination of the d e f i c i e n c i e s of the SCEPTRE data. P r e c i p i t a t i o n radar i s a v i a b l e source of hydrometeorological data. This study has explored the c a p a b i l i t i e s and inherent l i m i t a t i o n s of one o p e r a t i o n a l source of radar p r e c i p i t a t i o n data. From the r e s u l t s obtained, recommendations f o r improvements t o the system to enhance i t s s u i t a b i l i t y f o r a p p l i c a t i o n s to engineering hydrology have been suggested. 107 REFERENCES AND BIBLIOGRAPHY Ackerman, B., 1959: "Orographic-Convective P r e c i p i t a t i o n as Revealed by Radar", Physics of  P r e c i p i t a t i o n , American Geophysical Union, Washington, D.C, pp. 79-85. [AES 81] 1981: Flood Hydrology Guide f o r Canada: Hydrometeoroloqical Techniques, W. I . Pugsley, e d i t o r , Atmospheric Environment S e r v i c e P u b l i c a t i o n CL13-81, Downsview, On t a r i o . [Aoya78] Aoyagi, J . , 1978: "Ground C l u t t e r R e j e c t i o n by MTI Weather Radar", P r e p r i n t s , 18th Conference on Radar  Meteorology ( A t l a n t a ) , American M e t e o r o l o g i c a l S o c i e t y , Boston, pp. 358-363. 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[Wils79] Wilson, J.W. and Brandes, E.A., 1979: "Radar Measurement of R a i n f a l l - A Summary", B u l l e t i n of the American M e t e o r o l o g i c a l S o c i e t y , v o l . 60, no. 9, pp. 1048-1058. 113 APPENDIX A SCEPTRE Radar Measurement A l t i t u d e s Corrected f o r Earth Curvature and Standard Beam R e f r a c t i o n SCEPTRE Radar Beam Measurement A l t i t u d e ( C o r r e c t e d f o r Standard Beam R e f r a c t i o n and E a r t h C u r v a t u r e ) (metres) Range Beam E l e v a t i o n Angle ( m e t r e s ) ( d e g r e e s ) 0.50 0.80 1. 19 1 .60 2. 10 2.60 3. 19 3.88 4.69 5.60 6.69 7 .88 9.30 1 1 . 10 13. 19 2000. 18. 28. 42. 56. 74. 91 . 111 . 135. 163. 195. 232. 273. 321. 381 . 449 4000. 36. 57. 84. 113. 147. 182. 223. 271 . 327. 390. 465. 546. 642. 761 . 897 6000. 54. 86. 127. 169. 222. 274. 335. 407. 491 . 586. 698. 819. 963. 1 142. 1347 8000. 73. 115. 169. 227. 296. 366. 448. 544. 656. 782. 931 . 1093. 1285. 1524. 1796 1OO00. 93. 145. 213. 284. 372. 459. 561 . 681 . 821 . 978. 1165. 1367. 1607. 1906. 2246 12000. 112. 175. 257. 343. 447. 552. 675. 818. 987 . 1175. 1399. 1642. 1930. 2289. 2697 14000. 135. 208. 303. 403. 525. 647. 791 . 958. 1 154. 1374. 1636. 1919. 2255. 2673. 3150 16000. 155. 239. 348. 462. 602. 741. 905. 1096. 1321 . 1572. 1871. 2195. 2578. 3057. 3601 18000. 176. 270. 393. 522. 678. 835. 1020. 1235. 1487. 1770. 2106. 2471 . 2902. 3440. 4053 20000. 198. 302. 438. 581 . 756. 930. 1135. 1374. 1654. 1968. 2342. 2747. 3226. 3824. 4505 22000. 221. 337. 486. 644. 835. 1027 . 1252. 1516. ' 1824 . 2169. 2580. 3026. 3553. 4209. 4957 24000. 244. 369. 533. 704 . 913. 1122. 1368. 1656. 1992. 2369. 2817. 3303. 3878. 4596. 5412 26000. 266. 402. 579. 765. 992. 1218. 1485. 1796. 2160. 2568. 3054. 3581. 4203. 4981 . 5865 28000. 291 . 438. 629. 829. 1073. 1316. 1604. 1939. 2329. 2768. 3292. 3859. 4529. 5367. 6319 30000. 315. 472. 676. 891. 1152. 1413. 1721 . 2080. 2500. 2971 . 3532. 4139. 4857. 5755. 6775 32000. 339. 506. 724. 953. 1232. 1510. 1838. 2222. 2670. 3172. 3770. 4418. 5184. 6141. 7229 34000. 365. 543. 775. 1018. 1314. 1610. 1958. 2366. 2842 . 3375. 4011 . 4699. 5513. 6530. 7686 36000. 390. 579. 824. 1081 . 1394. 1708. 2077. 2508. 3012. 3577. 4250. 4979. 5841 . 6917. 8141 38000. 417 . 616. 875. 1146. 1477. 1808. 2198. 2653. 3185 . 3781 . 4491 . 5261 . 6171 . 7305. 8597 40000. 443. 652. 924. 1210. 1559. 1907. 2317. 2796. 3357. 3984. 4731 . 5542. 6499. 7695. 9055 SCEPTRE Radar Beam Measurement A l t i t u d e ( C o r r e c t e , Ra"9e B e a m E ( m e t r e s ) 0.01 0.01 0.02 0.03 0.04 0.05 0.06 420O0. 471 . 691 . 977. 1277. 1643. 2008. 2439 44000. 497. 728. 1027. 1342. 1725. 2108. 2559 46000. 526. 767. 1080. 1409. 1810. 2210. 2682 48000. 554. 805. 1131 . 1475. 1893. 2310. 2803 50000. 583. 845. 1185. 1543. 1978. 2413. 2926 52000. 614. 886. 1239. 1611 . 2064. 2517. 3050 54000. 642. 925. 1292. 1678. 2149. 2618. 3172. 56000. 673. 966. 1347. 1747. 2235. 2723. 3297. 58000. 704. 1008. 1403. 1817. 2322. 2827. 3422. 60000. 736. 1050. 1459. 1887. 2410. 2932. 3548. 62000. 766. 1091. 1513. 1956. 2496. 3036. 3671. 64000. 799. 1134. 1570. 2027. 2585. 3142 . 3798. 66000. 832. 1178. 1627. 2098. 2673. 3248. 3925. 68000. 866. 1222. 1684. 2170. 2763. 3354. 4052. 70000. 900. 1266. 1742. 2243. 2852. 3462. 4179. 72000. 934. 1311 . 1801 . 2315. 2943. 3569. 4307. 74000. 969. 1356. 1859. 2388. 3033. 3677. 4436. 76000. 1004. 1402. 1919. 2462. 3124. 3785. 4565. 7SOOO. 1039. 1448 . 1978. 2536. 3215. 3894. 4694. 80000. 1076. 1494 . 2038. 2610. 3307. 4003. 4824 . I f o r Standard Beam R e f r a c t i o n and E a r t h C u r v a t u r e ) (metres) e v a t l o n Angle degrees) 0.07 0.08 0. 10 0. 12 0. 14 0. 16 0. 19 0.23 2942. 3530. 4189. 4974. 5825. 6830. 8083. 9511 3086. 3702. 4392. 5215. 6106. 7159. 8474. 9970 3232. 3877. 4598. 5458. 6390. 7490. 8866. 10427 3377. 4050. 4803. 5700. 6672. 7820. 9255. 10887 3525. 4225. 5009. 5944. 6956. 8153. 9648. 11347 3672. 4401. 5217. 6188. 7241 . 8483. 10O38. 11805 3819. 4575. 5422. 6431 . 7525. 8817 . 10431. 12266. 3967. 4752. 5630. 6676. 7810. 9150. 10824. 12727. 4116. 4929. 5838. 6922. 8096. 9484. 11216. 13187. 4266. 5106. 6045. 7166. 8381 . 9817. 11610. 13649. 4414. 5282. 6254. 7413. 8668. 10152. 12005. 14111 . 4564. 5461 . 6464. 7660. 8956. 10487. 124O0. 14574. 4714. 5639. 6674. 7907. 9243. 10822. 12795. 15035. 4866. 5818. 6885. 8155. 9532. 11158. • 13189. 15499. 5017. 5998. 7095. 8403. 9820. 11493. 13585. 15963. 5169. 6178. 7307. 8650. 10107. 11830. 13981. 16427. 5321 . 6358. 7516. 8899. 10397. 12167. 14378. 16892. 5474. 6539. 7728. 9148 . 10687. 12505. 14776. 17357. 5627. 6718. 7941 . 9398. 10977. 12843. 15173. 17823. 5781 . 6902 . 8154 . 9648. 11268. 13181. 15572. 18289. V SCEPTRE Radar Beam Measurement A l t i t u d e ( C o r r e c t e d f o r S t a n d a r d Beam R e f r a c t i o n and E a r t h C u r v a t u r e ) (metres) Range Beam E l e v a t i o n Angle ( m e t r e s ) ( d e g r e e s ) 0.01 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0. 10 0. 12 0. 14 0. 16 0. 19 0.23 82000. 1112. 1541. 2099. '2685. 3399. 4113. 4954. 5935. 7084. 8367. 9899. 11559. 13520. 15970. 18755 84000. 1149. 1589. 2160. 2760. 3492. 4223. 5084. 6089. 7266. 8583. 10150. 11850. 13859. 16369. 19222 86000. 1186. 1636. 2221 . 2836. 3585. 4333. 5215. 6244. 7449. 8797. 10404. 12142. 14199. 16768. 19689 88000. 1224. 1684. 2283. 2912. 3678. 4444. 5346. 6400. 7632. 9012. 10656. 12437. 14539. 17168. 20157 90000. 1262. 1733. 2345. 2988. 3772. 4556. 5478. 6555. 7816. 9227. 10908. 12730. 14880. 17568. 20625 92000. 1300. 1782. 2408. 3065. 3867. 4667. 5610. 6711 . 8000. 9442. 11161. 13023. 15223. 17969. 21093 94000. 1341. 1833. 2473. 3143. 3961 . 4779. 5743. 6868. 8185. 9658. 11414. 13316. 15564. 18370. 21562 96000. 1381 . 1883. 2536. 3222. 4059. 4894. 5878. 7027. 8372. 9874. 11667. 13610. 15906. 18773. 22031 98000. 1420. 1933. 2600. 3301. 4154. 5007. 6012. 7184. 8557. 10093. 11923. 13905. 16248. 19175. 22500 100000. 1461. 1984. 2664. 3379. 4250. 5120. 6145. 7342. 8743. 10310. 12178. 14202. 16591. 19577. 22972 1020O0. 1503. 2037. 2731 . 3460. 4348. 5236. 6280. 7500. 8929. 10528. 12433. 14497. 16936. 19980. 23443 104OOO. 1544. 2089. 2796. 3540. 4445. 5350. 6416. 7661 . 9118. 10748. 12688. 14792. 17279. 20385. 23913. 106000. 1586. 2141. 2862. 3619. 4543. 5465. 6552. 7820. 9305. 10966. 12945. 15090. 17623. 20788. 24385. 108000. 1630. 2195. 2930. 3702. 4642. 5582. 6689. 7979. 9492. 11185. 13202. 15387. 17969. 21192. 24858. 110000. 1672. 2248.' 2996. 3782. 4740. 5697. 6825. 8141 . 9682. 11406. 13460. 15684. 18314. 21598. 25330. 112000. 1715. 2301 . 3063. 3863. 4839. 5813. 6961. 8302. 9870. 11626. 13717. 15983. 18659. 22003. 25802. 114000. 1760. 2357. 3132. 3947. 4940. 5932. 7100. 8464. 10061. 11848. 13974. 16281. 19006. 22408. 26277. 116000. 1803. 2411 . 3200. 4029. 5039. 6048. 7237. 8625. 10250. 12068. 14234. 16581. 19352. 22816. 26750. 118OO0. 1849. 2467. 3270. 4113. 5141 . 6167. 7377. 8789. 10441. 12291. 14492. 16880. 19700. 23221. 27226. 120OO0. 1894. 2522. 3338. 4196. 5241 . 6285. 7515. 8951 . 10631. 12512. 14753. 17180. 20047. 23630. 27700. SCEPTRE Radar Beam Measurement A l t i t u d e Range (m e t r e s ) 0.01 0.01 0.02 0.03 0.04 0.05 1220CO. 1941 . 2579. 3409. 4281 . 5344. 6405 124000. 1988. 2637. 3480. 4367. 5447. 6525 12G000. 2034. 2693. 3550. 4451 . 5548. 6644 128000. 2082. 2752. 3622. 4537. 5652. 6765 130000. 2130. 2810. 3695. 4624. 5754. 6885 132000. 2177. 2868. 3766. 4709. 5859. 7007 134O00. 2226. 2928. 3839. 4797. 5964. 7130 136000. 2276. 2988 . 3913. 4885. 6069. 7253 138000. 2324. 3046. 3985. 4972. 6173. 7374 140000. 2375. 3108. 4060. 5060. 6280. 7498 142000. 2426. 3169. 4135. 5150. 6386. 7622 144000. 2477. 3231 . 4210. 5240. 6494. 7746 146OO0. 2529. 3293. 4286. 5330. 6601 . 7871 148000. 2581 . 3356. 4363. 5420. 6709. 7997 150000. 2634. 3419. 4439. 5511 . 6818. 8121 152000. 2687. 3483. 4517. 5603. 6925. 8247 154000. 2741. 3547. 4594. 5695. 7034. 8373 156000. 2795. 3611 . 4672. 5787. 7144. 8501 158OO0. 2849. 3676. 4751 . 5880. 7254 . 8628 160000. 2904. 3741 . 4830. 5973. 7366. 8756 C o r r e c t e d f o r S t a n d a r d Beam R e f r a c t i o n and E a r t h Beam E l e v a t i o n ( d e g r e e s ) Angle 0.06 0.07 0.08 0. 10 0. 12 0. 14 7656 9115. 10824. 12736. 15011. 17480 7794 9278. 11015. 12958. 15273. 17782 7936 9443. 11208. 13182. 15535. 18082 8077 9609. 11401. 13405. 15795. 18384 8218 9773. 11593. 13631. 16057. 18687 8360 9939. 11788. 13856. 16318. 18989 8503 10106. 11983. 14081. 16582. 19293 8647 10271. 12176. 14307. 16846. 19597 8788 10439. 12372. 14534. 17110. 19900 8933 10607. 12568. 14761. 17373. 20205. 9077 10776. 12764. 14987. 17638: 20510. 9222 10945. 12959. 15216. 17903. 20816. 9368, 11114. 13157. 15444. 18169. 21122. 9514 , 11282. 13354. 15673. 18436. 21427. 9658. 11452. 13553. 15903. 18702. 21734. 9805. 11623. 13751. 16133. 18969. 22042. 9952. 11794. 13950. 16363. 19237. 22349. 10099. 11966. 14150. 16594. 19505. 22658. 10247. 12137. 14349. 16825. 19773. 22967. 10396. 12310. 14550. 17056. 20042. 23276. C u r v a t u r e ) (metres) 0.16 0.19 0.23 20396. 24036. 28176 20743. 24445. 28651 21093. 24853. 29128 21444. 25263. 29603 21792. 25673. 30081 22143. 26081. 30557 22493. 26493. 31036 22845. 26902. 31515 23197. 27314. 31993 23550. 27726. 32473 23901. 28139. 32953 24255. 28550. 33432 24609. 28963. 33913 24963. 29377. 34394 25318. 29792. 34876 25673. 30206. 35358. 26029. 30621. 35841. 26385. 31037. 36322. 26739. 31453. 36806. 27096. 31869. 37290. APPENDIX B Summary of AES D a i l y Raingauge Locations and Gauge/Rada Measurements Station Name Location UTM Coordinate Latitude Longitude North East Gauge/Radar Measurements Dec 20 Dec 21 Feb 12 Feb 13 F«b 14 Agassiz CDA 49" 15' Alouette Lake 49' 17' Bamberton Ocean Cement 48' 35' Buntzen Lake 49* 23' Burnaby Capitol H i l l 49' 17' Burnaby Cariboo Dam 49' 15' Burnaby East 49' 13' Burnaby Mtn Terminal 49' 16' Burnaby Simon Fraser U 49' 17' Central Saanlch I s l View 48' 34' Central Saanlch Veyaness 48' 35' Chll1Iwack 49" 07' Ch1l11wack Gibson Road 49' 11' Coqultlam Como Lake Ave 49* 16' Coqultlam Lake 49' 22' Cordova Bay South 48* 31' Cowlchan Bay 48' 44' Cowlchan Lake Weir 48' 50' Cultus Lake 49' 05' Delta Ladner South 49* 04' Delta Tsawwassen Beach 49* 01' Duncan Forestry 48' 47' Edenbank SardIs 49' 08' Esqulmalt Metoc 48' 26' Gal1ano South 2 48' 53' Gambler Harbour 49' 27' Ganges Mansel1 Rd 48* 52' Gibsons Gower Point 49* 23' Haney Corrl Instn 49' 15' Haney East 49* 12' Haney UBC RF Admin 49* 16' Hollyburn Ridge 49' 22' Hopkins Landing 49' 28' loco Refinery 49* 18' Langley P r a i r i e 49' 09' Mayne Island 48' 50' Metchosln 48' 23' Metchosln Happy Valley 48' 25' M111 Bay Kllmalu 48' 39' Mlsslon 49' 08' Mission Hartley Rd 49' 15' Mission West Abbey 49* 09' Nanlamo Departure Bay 49' 13' N Vancouver Capllano 49' 20' N Vancouver Cleveland 49' 22' N Vancouver Cloverly 49' 19' N Vane Grouse Mtn Resort 49' 23' N Vancouver Lynn Creek 49* 22' N Vancouver Redonda Dr 49' 22' * Mixed r a i n and snow: snowfall 121* 46' 5455000 590000 12 /16 122' 29' 5459100 537500 54 /21 123" 31' 5381400 461600 / 122' 52' 5469000 510000 58 /28 122' 59' 5459000 501000 33 /25 122' 55' 5455000 506000 34 /20 122' 45' 5450500 503500 / 122* 56' 5457000 505000 33 /20 122' 55' 5458500 506000 41 /27 123' 22' 5379700 473000 16 /11 123' 25' 538140O 469200 15 /12 122' 06' 5441700 566400 19 /13 121' 53' 5448300 5813CO 19 /16 122' 52' 5456600 5097CO 30 /22 122' 48' 5466500 516300 / 123' 22' 5373600 473000 / 123' 35' 5396700 457000 25 /10 124' 04' 5408200 422300 / 121' 59' 5436300 574500 14 / i o 123' 05' 5434600 494000 31 /22 123' 06' 5429900 492700 28 /20 123' 41' 5403400 449700 34 /16 121' 58' 5442600 57580O 17 /1T 123* 26' 5364000 468000 13 / i o 123" 21 ' 5414400 474400 23 /12 123' 26' 5476700 468500 43 /15 123* 30' 5412500 463300 30 /15 123' 32' 5470100 461100 28 /12 122' 31 ' 5454400 535100 47 /31 122' 34' 5450OO0 531500 37 /24 122" 34' 5456600 531200 / 123' 12' 5469400 486200 60 /18 123' 29' 5474500 465300 36 /17 122' 53' 5461COO 508500 43 /28 122' 39' 5443700 525900 40 /34 123' 16' 5408700 480400 22 /14 123' 32' 5358700 460400 12 / 8 123' 33' 5362500 460600 14 /10 123' 33' 5388400 459200 21 /10 122' 18' 5443000 551000 28 /18 122' 14' 5455300 555800 / 122' 16' 5444600 5533CO 28 /28 123' 57' 5451100 430500 15 /10 123' 06' 54640O0 492700 37 /21 123' 06' 5467300 492300 42 /20 123' 03' 5462900 496700 30 /19 123' 05' 5469400 494000 59 /22 123" 02' 5467300 498100 50 /22 123' 05' 5467500 493500 40 /21 converted to water equivalent and 14 /14 12 /10 25 /IB 11 /17 32 /13 27 /11 20 /20 33 /32 / / / / 62 /18 39 /16 34 /21 40 /25 38 /15 23 /13 24 /16 10 /II 27 /12 23 /11 15 /14 12 /13 / / / / 37 /11 23 /II 22 /14 11 /14 34 /18 24 /16 15 /16 12 /13 13 /10 16 /11 16 /16 11 / 1 11 /10 8 /12 10 /14 14 / 3 25 /II 23 /11 24 /18 33 /23 22 /15 17 /12 25 /18 10 /20 34 /15 25 /13 15 /17 9 /16 / 37 /17 36 /25 45 /25 / / / / 16 / 7 13 / 7 7 / 8 15 / 8 / / / / 15 / 8 22 /13 25*/15 12 /16 19 /15 21 /16 10 /12 12 / 3 16 /13 20 /16 10 /12 4 / 1 20 / 7 16 / 9 16 / 8 11 / 5 17 /13 18 /12 24 /20 9 /17 11 / 8 10 / 6 16 /16 9 / 7 16 / 9 18 /II 13 /11 4 / 0 40 /13 26 /II 13 / 7 7 / 6 2 /11 13 /11 1 0 / 8 6 / 0 29 /10 18 /11 9 / 5 4 / 0 30 /17 / / / 23 /14 / / / / 24 /12 15 /16 26 /27 59 /11 40 /14 29 /15 33 /14 47 /13 35*/15 17 / 6 13 / 2 34 /19 / / 18 /16 20 /16 42 /15 10 /20 12 /15 15 / 9 14 /11 14 /14 7 / 0 1 1 / 9 13 / 8 14 /15 7 / 8 13 / 9 12 / 9 16 /15 27 / 9 19 / 7 16 / 9 14 /11 18 /10 23 /IS 26 /12 24 /18 14 /20 / 22 /13 25 /23 37 /30 23 /18 25 /13 21 /21 14 /22 20 / 5 14 / 8 9 / 5 3 / 2 40 /17 25 /17 17 /16 19 /11 50 /15 / / / 40 /13 25 /13 23 /18 18 /18 72 /16 51*/17 13 /20 10 /20 55 /16 / / / 46 /17 27 /15 / / added to r a i n f a l l value Station Name Location UTM Coordinate Latitude Longitude North East Gauge/Radar Measurements Dec 20 Dec 21 Feb 12 Feb 13 Feb 14 N Vancouver Seymour Blvd 49* 19' 123* 01' 5462500 498700 43 /22 32 /14 25 /14 21 /19v 23 /19 N Vane Sonara Dr 49' 22' 123" 06' 5467000 491000 41 /20 32 /15 / / / N Vancouver Upper Lynn 49* 21 ' 123" 02' 5465700 498000 / / / / / N Vancouver Wharves 49' 19' 123' 07' 5462400 491500 30 /19 40 /14 19 /15 22 /14 10 / 9 Piers Island 48' 42' 123' 25' 5395000 469400 19 /12 13 / 9 12 / 9 13 /13 16 / 2 P i t t Meadows STP 49' 13' 122' 42' 5450400 522000 37 /24 26 /13 28 /13 13 /16 18 /16 P i t t Polder 49' 18' 122' 38' 5460700 526700 43 /28 31 /15 24 /13 16 /21 31 /27 Point Atkinson 49' 20' 123" 16' 5464O0O 480800 18 /14 23 /11 20 /14 10 /12 4 / 6 Port Mellon 49* 31' 123' 29' 5485300 464700 44 /16 45 /14 33 /12 48 /14 19 / 8 Port Moody Gulf 011 Rfy 49* 17' 122" 53' 5458500 508300 42 /19 41 /II 26 /12 16 /16 15 /16 Richmond Geal Rd 49' 09' 123* 10' 5444000 488000 27 /16 19 /11 24 /15 12 /12 3 / 3 Richmond Nature Park 49' 10' 123* 06' 5446300 493200 31 /19 21 /12 22 /14 15 /13 12 / 6 Roseda1e 49* 11' 121* 48' 5448O0O 587lOO 12 /12 16 /11 14 /H 22 /21 12 /18 Saanlchton CDA 48* 37' 123" 25' 5385300 469500 18 /12 14 / 9 15 /H 14 /13 14 / 4 Sa l t s p r i n g Is Cusheon Lk 48* 49' 123" 27' 5406500 466400 24 /13 16 / 8 16 / 9 12 / 8 8 / 1 Sa l t s p r l n g St Mary's L 48* 53' 123" 33' 5414400 460200 28 /18 21 /11 16 /11 1 0 / 9 1 0 / 0 Saturna Island Light 48' 47' 123' 03' 5403200 496700 5 /14 2 / 9 9 /13 9 /12 5 / 0 Seymour F a l l s 49' 26' 122' 58' 5476200 502500 56 /28 72 /20 47*/21 73 /34 47 /26 Shawn1gan Lake 48* 39' 123" 37' 5389O00 454300 25 /13 19 / 7 21 /11 18 /12 26 /14 Sooke 48" 22' 123' 44' 5357OO0 446000 16 / 7 12 / 8 14 / 8 13 / 9 17 / 8 Sooke Lake North 48' 34' 123" 39' 5380500 452100 28 /12 16 / 7 25 /15 26 /17 36 /19 South Pender Island 48' 45' 123' 13' 5399000 484000 18 /10 11 / 9 10 / 9 14 /13 6 / 1 Sumas Canal 49' 07' 122' 07' 544050O 5650O0 22 /13 16 /11 24 /11 23 /18 11 /23 Surrey Kwantlen Park 49* 12' 122' 52' 5448700 510300 31 /20 21 /10 / / / Surrey Municipal Hall 49" 06' 122* 50' 5439000 512600 34 /22 47 /12 30 /12 12 /15 6 / 8 Surrey Newton 49' 08' 122* 51 ' 5443O00 5110O0 31 /18 24 / 8 13 /14 15 /13 20 /11 Surrey Sunnyslde 49" 03' 122' 48' 5433000 5150O0 30 /29 19 /14 29 /15 16 /16 6 / 7 Vancouver City Hall 49' 17' 123' 07' 5456300 491800 / / / / / Vancouver Dunbar South 49' 15' 123' 11' 5449900 486800 28 /16 26 /10 21 /13 14 /12 6 / 5 Vancouver UBC 49* 15' 123' 15' 5456700 481500 29 /15 24 /II 21 /14 11 /12 5 / 3 Vancouver West 10th 49' 16' 123" 10' 5456500 488700 / / 23 /17 / / V i c t o r i a Gordon Head 48' 28' 123' 18' 5369O0O 477500 13 / 9 10 / 8 7 / 7 13 /16 8 / 3 V i c t o r i a Highland 48' 30' 123' 30' 5371700 463000 22 /10 9 / 8 18 / 8 17 /13 2 0 / 9 V i c t o r i a Marine 48' 22' 123' 45' 5357500 444500 12 / 7 16 / 8 17 /10 7 / 9 14 / 9 V i c t o r i a P h y l l i s Street 48* 27' 123' 16' 5366500 480000 12 / 9 7 / t 7 / 6 15 /15 5 / 3 V i c t o r i a Portage Inlet 48' 27' 123' 26' 5367000 468000 / 1 8 1 1 / 6 16 /15 8 / 7 V i c t o r i a Princess Ave 48' 26' 123" 21 ' 5364000 474300 15 / 9 9 / 7 / 5 15 /15 8 / 3 V i c t o r i a Prospect Lake 48' 31 ' 123* 26' 5366000 471500 16 / 9 12 / 8 14 / 5 14 /15 14 / 4 V i c t o r i a U Vic 48' 28' 123' 20' 5367600 477000 / / 7 / 4 15 /14 / W Vane Ballantree Place 49' 22' 123" 08' 5467400 4907OO 49 /20 49 /15 18 /16 26 /16 26 /14 W Vane Capllano GCC 49' 21 ' 123" 07' 5466700 491100 44 /20 47 /15 19 /16 / / W Vancouver Dundarave 49' 20' 123" 1 1' 5464600 486600 41 /17 26 /13 / / / West Vancouver Mathers 49' 20' 123' 11 ' 5465100 486400 / / / / / Whalley Forest Nursery 49' 11' 122" 50' 5447200 512600 / / 21 /14 / / White Rock STP 49' 01' 122' 46' 5429000 517000 29 /20 17 /II 22 /14 10 /13 4 / 6 WI111am Head 48' 21 ' 123" 32' 5354000 4605OO 10 / 7 10 / 9 9 / 9 13 /13 4 / 6 * Mixed rain and snow: snowfall converted to water equivalent and added to r a i n f a l l value APPENDIX C Flowchart Showing CAPPI Image G r i d E x t r a c t i o n , E r r o r C o r r e c t i o n , Data Tr a n s f e r , and Image Generation Processes 122 c a l c u l a t e radar Measurement a l t l t u d a a RORELEV.FTN chack data a r r o r s , aalact Image araa, convart DVIP valuas to r a i n f a l l , produca aaq. a cum. luge f i l e s a hyetogxapha GlNIMAGE character convert 1on f i l e r a f o r and •at produce leohyeta! or 3-d aurfaca representst1ona 1 2 3 tannine! emulat ion a f i l e t ranefer TERM.BAS F I 11n* • d l t o p E0LIN.COM cleaned-up l u g e f i l e i M g a d l a p l a y » I n t e r a c t i v e ana 1 ya 1 a RORIMAGE.BAS r a p i d ••quant 1a1 Image d l s p l ay 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