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Digital signal processing of UHF radio echo sounding data from northern Ellesmere Island Prager, Bradley Thomas 1983

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DIGITAL SIGNAL PROCESSING OF UHF RADIO ECHO SOUNDING DATA FROM NORTHERN ELLESMERE ISLAND by BRADLEY THOMAS PRAGER B.Sc.  (Honours Geophysics), U n i v e r s i t y of A l b e r t a , 1980  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE  REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in  THE  FACULTY OF GRADUATE STUDIES  (Department of Geophysics  and Astronomy)  We accept t h i s t h e s i s as conforming to the r e q u i r e d  THE  standard  UNIVERSITY OF BRITISH COLUMBIA October  1983  © Bradley Thomas Prager, 1983  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of  requirements f o r an advanced degree at the  the  University  o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make it  f r e e l y a v a i l a b l e f o r reference  and  study.  I further  agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may  be granted by the head of  department or by h i s or her  representatives.  my  It i s  understood t h a t copying or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l gain  s h a l l not be allowed without my  permission.  Department o f  Geophysics and  Astronomy  The U n i v e r s i t y of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date October 4,  DE-6  (3/81)  1983  written  ABSTRACT This signal  thesis  is a  processing  processing  p r e l i m i n a r y attempt  techniques  i c e radar  processing  i s designed noise  gain to  control,  enhance  and ' i n c r e a s i n g  and  the  the  digital  data.  i n s p i r e d many of the techniques: l i n e a r  d i f f e r e n t i a t i n g , automatic  reducing  to  to apply  Seismic  filtering,  stacking.  radar  The  section  amplitude  of  by  small  r e f l e c t i o n s , making r e f l e c t i o n s e a s i e r to l o c a t e . Once r e f l e c t i o n s have been reflector  properties  can  be  located,  if  sufficiently  the  depth  and  i n t e r p r e t e d from the data. Ice  t h i c k n e s s and power r e f l e c t i o n c o e f f i c i e n t obtained;  i c e thickness  to  the  (PRC) can always be  reflector  l a r g e change, the propagation  loss  undergoes rate  a  of the  i c e can a l s o be c a l c u l a t e d . The p r o c e s s i n g and i n t e r p r e t a t i o n techniques are a p p l i e d to  i c e radar  data  from a 1981 survey on northern Ellesmere  I s l a n d . Ice t h i c k n e s s , PRC, and propagation following Milne  areas  and  surrounding exceeding  Ward  are c a l c u l a t e d : Milne and D i s r a e l i Hunt  Ice  Shelves,  and  a  small  Glaciers, i c e cap  Mt. Oxford. The g l a c i e r s have a maximum t h i c k n e s s 700 m, a b a s a l PRC of about  propagation  l o s s r a t e f o r the  -30 dB, and a  typical  l o s s r a t e of 0.025 dB/m (at 840 MHz). The t h i n n e r  i c e areas of the Milne  and  Ward  Hunt  Ice  Shelves  produce  e i t h e r no b a s a l r e f l e c t i o n or only a f a i n t r e f l e c t i o n ; t h i s i s taken t o i n d i c a t e b a s a l a c c r e t i o n of soaking, underneath  produced  by  meltwater  the i c e s h e l v e s . i i  brackish  i c e or  brine  flowing out from the f i o r d s  TABLE OF CONTENTS Abstract  ii  List  of Tables  List  of F i g u r e s  v vi  Acknowledgements 1.  2.  3.  4.  viii  Introduction  1  1.1  Data P r o c e s s i n g  and  1.2  Glaciological Island  Studies  Processing  Radio Echo Sounding on  Northern  4 Ellesmere  D i g i t a l Radio Echo Sounding Data  6 9  2.1  Introduction  9  2.2  Recording the Data  9  2.3  Processing  to Produce I n t e r p r e t a b l e S e c t i o n s  12  2.3.1  Stacking  15  2.3.2  High-Pass F i l t e r i n g  2.3.3  Differentiating  18  2.3.4  Automatic Gain C o n t r o l  20  2.3.5  Low-Pass F i l t e r i n g  23  2.3.6  Display  23  ...18  I n t e r p r e t i n g a D i g i t a l Radar S e c t i o n  31  3.1  Introduction  31  3.2  Locating Reflections  31  3.2.1  32  E f f e c t s Which Obscure R e f l e c t i o n s  3.3  Ice Thickness and  3.4  R e f l e c t i o n and  Layer Separation  Propagation  37  Losses  39  3.4.1  Power R e f l e c t i o n C o e f f i c i e n t  40  3.4.2  D i e l e c t r i c Loss and  43  the Loss Tangent  Radio Echo Sounding on Northern Ellesmere iii  Island  47  4.1  4.2  Introduction  47  4.1.1  Areas Flown and N a v i g a t i o n  48  4.1.2  Accuracy of R e s u l t s  50  Mt. Oxford Ice Glaciers . ,  Cap  and the Milne and  Disraeli  4.2.1  Ice Thickness  53  4.2.2  Propagation Loss Rate and the Basal PRC  60  4.3 Milne Ice Shelf  68  4.3.1  Ice Thickness  70  4.3.2  Basal Power R e f l e c t i o n C o e f f i c i e n t  70  4.4 Ward Hunt Ice Shelf  5.  51  72  4.4.1  Ice Thickness  77  4.4.2  D i e l e c t r i c Loss and Basal PRC  77  4.4.3  The  PRC  of the Lake Ice/Sea  Ice I n t e r f a c e  Concluding Remarks  ...79 ....82  5.1  Data P r o c e s s i n g and Radio Echo Sounding  5.2  Radio Echo Sounding  on Northern E l l e s m e r e I s l a n d  References  82 ..83 86  iv  LIST OF TABLES 2.1  System parameters f o r the UBC  4.1  Propagation  840 MHz  l o s s r a t e and b a s a l PRC  v  radar  10 64  LIST OF  FIGURES  1.1  The  study area: Ellesmere I s l a n d , N.W.T., Canada  1.2  Areas sounded in 1966  2.1  Stacking  2.2  High-pass f i l t e r i n g  2.3  Differentiating  20  2.4  Automatic gain c o n t r o l  22  2.5  Low-pass f i l t e r i n g  24  2.6  A-scope, v a r i a b l e area, and  2.7  Grey-scale display  28  2.8  Colour r e f l e c t i v i t y d i s p l a y  30  3.1  D i f f r a c t i o n patterns  36  3.2  Multiple  36  4.1  Overland f l i g h t  4;2  Radar s e c t i o n  from the Mt.  4.3  Radar s e c t i o n  from the D i s r a e l i G l a c i e r  55  4.4  Radar s e c t i o n  from the Milne G l a c i e r  56  4.5  Depth p r o f i l e  for the Mt.  57  4.6  Depth p r o f i l e  for the D i s r a e l i G l a c i e r  4.7  Depth p r o f i l e f o r the M i l n e G l a c i e r  4.8  Echo s t r e n g t h  versus depth f o r the Mt.  4.9  Echo s t r e n g t h  versus depth f o r the D i s r a e l i G l a c i e r  4.10  Echo s t r e n g t h  versus depth for the Milne G l a c i e r  4.11  D i s t r i b u t i o n of b a s a l l y - r e f l e c t e d power  66  4.12  F l i g h t l i n e map  67  4.13  Radar s e c t i o n  from the Milne Ice Shelf  69  4.14  Ice t h i c k n e s s  map  71  and  2  1981  3 17 ...19  threshold  displays  reflections lines  26  52 Oxford i c e cap  Oxford i c e cap  58 59 Oxford i c e cap  f o r the M i l n e Ice Shelf  f o r the Milne Ice Shelf vi  54  61 ..62 63  4.15  Basal  PRC of the Milne Ice Shelf  4.16  Flight  4.17  Radar s e c t i o n from the Ward Hunt Ice Shelf  76  4.18  Ice-layer thickness  78  l i n e map f o r the Ward Hunt Ice Shelf  of the Ward Hunt Ice Shelf  vi i  73 74  ACKNOWLEDGEMENTS I  thank  suggestions  my  supervisor  and advice over  Dr.  Clarke  the long course  e s p e c i a l l y thank him f o r the thesis;  G.K.C.  opportunity  work  most aspects of i t have proven to be both  Narod,  his  of t h i s t h e s i s . I to  and c h a l l a n g i n g . I a l s o thank my "surrogate B.B.  for  on  this  interesting  supervisor",  Dr.  f o r h i s a s s i s t a n c e d u r i n g Dr. C l a r k e ' s one year  s a b b a t i c a l absence. I owe much of what I know about d i g i t a l and  processing  e s p e c i a l l y seismic p r o c e s s i n g to S. Levy and M. Lane,  of  the  University  experience  1981.  of  and d e t a i l e d  me g r e a t l y . The data  of  signal  British  Columbia.  Their  Defence  Narod and myself flight  support  Research of UBC.  aided  i n t h i s t h e s i s were a c q u i r e d i n  The f i e l d party c o n s i s t e d of M. Black and  the  practical  knowledge of seismic p r o c e s s i n g  I present  both  B.  Haagensen  Board P a c i f i c , and Dr. C l a r k e , Dr. I  am  grateful  f o r the e x c e l l e n t  provided the p r o j e c t by the aircrew of Canadian  Armed Forces a i r c r a f t  13803: Capt.  P.  Schoneberg,  Capt.  D.  M c G i l l , and M. C p l . K. H i l l . The to  the  accuracy  of the Milne Ice S h e l f n a v i g a t i o n owes  suggestions  of  C a l g a r y . Dr. D. Crabtree proofreading  and  M.  Jeffries  generated  of  the  U n i v e r s i t y of  the c o l o u r s e c t i o n .  over  the  last  Needed  e d i t i n g were s u p p l i e d by M. Maxwell and Dr.  C l a r k e . Dome Petroleum and a UBC graduate f e l l o w s h i p me  much  supported  two years of t h i s t h e s i s . Computing funds  were provided by NSERC grant A4327, and l o g i s t i c a l a D.S.S. c o n t r a c t . vi i i  support  by  1. INTRODUCTION M a g n e t i c a l l y - r e c o r d e d r a d i o echo digitally Columbia  processed  and  sounding  data  can be  enhanced. The U n i v e r s i t y of B r i t i s h  (UBC) 840 MHz a i r b o r n e i c e radar records the data i t  a c q u i r e s on analogue magnetic tape r a t h e r than on photographic film  (as i s t y p i c a l ) ;  through  an  digital  data.  the  analogue  tapes  can  a n a l o g u e - t o - d i g i t a l converter Signal  processing  and  to  be  replayed  produce  image  fully  enhancement  techniques can then be a p p l i e d to the data t o make them e a s i e r to  interpret. In  the  first  part  of t h i s t h e s i s I d i s c u s s the s i g n a l  p r o c e s s i n g techniques I apply to the UBC 840 MHz Digital  radar  p r o c e s s i n g t o enhance r a d i o echo sounding  data i s not  common because most r a d i o echo sounders record the acquire  on  immediately  photographic interpreted  film.  The  film  data  records  for ice thickness,  data.  but  they  can be  cannot  be  enhanced t o make r e f l e c t i o n s e a s i e r t o l o c a t e . In  the  second  interpretation  part  techniques  of  this  thesis  for calculating  UBC  840 MHz  established example  radar  data.  and  others  1969;  Neal  data  1976),  automated and a p p l i e d to d i g i t a l l y - r e c o r d e d In  l o s s r a t e s from  These techniques a r e now w e l l  for photographically-recorded  Robin  discuss  i c e thicknesses,  power r e f l e c t i o n c o e f f i c i e n t s , and propagation the  I  (see f o r and  can be  data.  the l a s t part of t h i s t h e s i s I d i s c u s s the r e s u l t s of  a p p l y i n g the p r o c e s s i n g and i n t e r p r e t a t i o n techniques to r a d i o echo  sounding  data  from  Ellesmere  1  Island,  N.W.T., Canada  2  (Figure  1.1). Arctic  Figure  I  include  propagation  Circle  1.1  ice  75°  The  35°  study  area:  thickness,  loss  rate  85°  Ellesmere  Arctic  75°  Circle  I s l a n d , N.W.T., C a n a d a .  power r e f l e c t i o n c o e f f i c i e n t ,  results  from  various  areas  on  and the  northern coast of Ellesmere I s l a n d (Figure 1 . 2 ) : the Ward Hunt and Milne Ice Shelves, the Milne and D i s r a e l i G l a c i e r s , and small  ice  cap surrounding Mt. Oxford  as the Mt. Oxford This  (which I s h a l l r e f e r to  ice cap f o r s i m p l i c i t y ) .  t h e s i s i s a p r e l i m i n a r y attempt at a p p l y i n g d i g i t a l  s i g n a l p r o c e s s i n g techniques to r a d i o echo sounding techniques  a  I  recorded data  use  are  demands  simple  data.  The  because the l a r g e q u a n t i t y of  computationally-efficient  processing.  3  Figure  1.2  Areas  sounded  i n 1966  and  1981.  I n t h i s t h e s i s I d i s c u s s t h e r e s u l t s f r o m t h e 1981 s o u n d i n g s (the sounded areas are shaded); Hatters1ey-Smith and others (1969) discuss ice t h i c k n e s s e s f r o m t h e 1966 s o u n d i n g s ( d e n o t e d by s o l i d lines).  This  simplicity  methods  disguises  required  the  sophisticated  data-handling  to make even the most elementary p r o c e s s i n g  f e a s i b l e . Because these d a t a - h a n d l i n g methods depend upon computer  hardware  and  o p e r a t i n g system,  not d i s c u s s t h e i r  implementation  for  how  details  Advanced closer  of  processing examination  would produce  these and of  the  i n t h i s t h e s i s I do  (see Prager  1982a  and  1982b  methods are implemented at  interpretation northern  r e s u l t s more, a c c u r a t e  the  techniques,  UBC). and  a  E l l e s m e r e I s l a n d data, and  detailed  than  the  4 p r e l i m i n a r y ones presented i n t h i s  1.1  DATA PROCESSING AND L i t t l e processing  sounding  data.  The  thesis.  RADIO ECHO SOUNDING is  applied  to  d i f f e r e n t i a t e d to allow the higher frequency r e f l e c t i o n  onsets  energy  backscattered  inclusions.  edges)  data  echo often  leading  sounding  radio are  (steep  received  analogue  to stand out from the lower by  reflector  roughness  frequency and  ice  The data are then recorded p h o t o g r a p h i c a l l y using  one of three formats: 1.  A-scope.  The  returned  power  o s c i l l o s c o p e and photographed.  is  displayed  on  The A-scope photographs  l a t e r be hand d i g i t i z e d on an x-y d i g i t i z e r , but extremely slow so only a few t r a c e s can be 2.  Z-scope.  The  Photographic  film  oscilloscope  screen  this  is  digitized.  section.  is  exposed  forming  a  the and  beam moved  intensity. across  continuous,  the  intensity  Large amounts of data can be recorded  using the Z-scope format, and the s e c t i o n s produced immediately  can  t r a c e i s swept down the o s c i l l o s c o p e screen  with the r e t u r n i n g power modulating  modulated  an  interpreted  for  ice  thickness.  r e c o r d i n g i s the most common format used with  can  be  Z-scope  radio  echo  sounding because s e c t i o n s c o n s i s t i n g of many t r a c e s can  be  p l o t t e d , and no f u r t h e r p r o c e s s i n g i s necessary. 3.  Echo s t r e n g t h measurement this  technique  (ESM).  Neal  (1976)  developed  to r e c o r d the maximum returned power from  an i n d i v i d u a l r e f l e c t o r . The  oscilloscope  time  base  is  5 switched o f f and the r e t u r n i n g power i n the  reflection  Photographic  of  film  oscilloscope  interest  a  window  i s plotted  i s exposed  and  screen; the envelope  moved  vertically. across  the  reflector  power  i f Z-scope  reflection or  the  of the image w i l l be the  maximum returned power i n the window. ESM can be calculate  around  used  coefficient  A-scope  recordings  to  of the are made  simultaneously to allow range d e t e r m i n a t i o n s . Watts and Wright record  radio  echo  (1981) used a sampling sounding  data  (from the Columbia  Alaska) on magnetic tape. Before sampling data  they  bandpass  filtered  gain to enhance l a t e - a r r i v i n g and  Wright  and r e c o r d i n g  low-amplitude  their  Watts  d i d not d i g i t i z e and f u r t h e r process t h e i r  data,  through  an  oscilloscope  to  standard Z-scope s e c t i o n s .  by  hand-digitized Neal  (1977)  A-scope  and  reflector  and  coefficient,  reflector  conductivity.  ice  One  records  Millar  process t h e i r data to make r e f l e c t i o n s  cannot  reflections.  reflections,  and  I  clearer,  but  power  analyzed reflection  dielectric permittivity  easily  therefore  then  re-examine the o r i g i n a l  use data.  been  (1981). They d i d not  characteristics: roughness,  has  obtain  this  information from processed data because the p r o c e s s i n g the  Glacier,  reflections.  Processing discussed  to  them and a p p l i e d a t i m e - v a r y i n g  but r e p l a y e d the magnetic tapes generate  oscilloscope  use  the  type  and of  affects  processed data to l o c a t e  located  reflections  to  6 The  UBC  840 MHz  ice  radar  uses a sampling time base,  analogous to that used by sampling o s c i l l o s c o p e s , to the  incoming  p u l s e s at 10 kHz.  Only one  taken;  hence the data can be recorded  These  tapes  converter  can  be  replayed  processing  sample per strobe i s  on audio magnetic  tape.  through an a n a l o g u e - t o - d i g i t a l  to produce f u l l y d i g i t a l  Digital  "strobe"  radar  data.  s i m i l a r to seismic p r o c e s s i n g  used by  companies e x p l o r i n g f o r o i l ( f o r example see Kanasewich can  then be a p p l i e d to enhance the d i g i t a l  processing  radar data.  reduces n o i s e , i n c r e a s e s r e s o l u t i o n ,  reflections  so  that  sections  indicate  and  the  data,  techniques  but  true  spatial  only  noise  GLACIOLOGICAL STUDIES ON Periodically,  reduction  huge  and  are d i s c u s s e d  "ice  islands"  calve  Ice Shelf l o s t almost 600  of i t s area d u r i n g  considerable produce can a hazard The  practical float  km  2  1963).  These  Ice  studied  L e v e l i n g and  seismic surveys  Hunt  are  of of  i c e i s l a n d s they Sea,  posing  rigs.  Shelf,  extensively  the i c e  the winter  calvings  southwards through the Beaufort  Hunt  from  I s l a n d (the Ward  i n t e r e s t because the  to o f f s h o r e d r i l l i n g Ward  thesis.  NORTHERN ELLESMERE ISLAND  Ellesmere  Hattersley-Smith  simple  in t h i s  s h e l v e s which f r i n g e northern  1962;  seismic  should be t r i e d on r a d i o echo sounding  r e s o l u t i o n - i n c r e a s i n g techniques  1.2  Seismic migrates  r e l a t i o n s h i p s of the r e f l e c t o r s . U l t i m a t e l y , a l l these processing  1975)  the  during the l a t e  largest 1950's and  show that the  shelf,  was  e a r l y 1960's.  average  thickness  7 i s 43 m (see composed ice  f o r example Crary  of  an  which  overlies  The  Lyons and  and  1960).  upper l a y e r c o n s i s t i n g of a  basement  i n t e r d i g i t a t i n g b r a c k i s h and 1955;  1958  Ragle 1962;  sea  The  shelf  iced f i r n and  lake  consisting  of  layer  i c e (see for example  Lyons and  others  1971  some  accumulated dust and Ragle  and  properties  and  1972).  a  heavy  (compared contains  to  ice  the  concentration  (1964)  cores  measured  lake  the  dielectric  taken from the Ward Hunt Ice  ice  layer  a high  affect  radio  or a g l a c i e r ) because i t ice  echo sounding for two  attenuated;  and  water i n t e r f a c e would be low the d i e l e c t r i c  in  would  1966  Ellesmere  Island  first  others  experiment, the Ward Hunt Ice S h e l f , the  Milne  and  northern  coast  Milne  and  (Hattersley-Smith  was and  Glaciers  ice/sea decrease  contrast.  Ice on northern sounded  i c e would  the r e f l e c t i v i t y at the  because the s a l t  would  reasons: a  r a d i o wave propagating through the h i g h - c o n d u c t i v i t y severely  Shelf.  conductivity  s a l t . A basal l a y e r of s a l i n e or b r a c k i s h  detrimentally  of  d e b r i s marks the i n t e r f a c e .  others  of  areas  They found that the basement i c e l a y e r has  several  glaciers  were sounded. The  D i s r a e l i G l a c i e r s vary  and 1966  power r e f l e c t e d from the  the tongues of the Milne and  radio  echo  1969). In and  this  Disraeli  i c e caps i n l a n d from the soundings show that  between 0 - 700  that the Ward Hunt Ice Shelf v a r i e s between The  Marshall  lake i c e l a y e r unconformably o v e r l i e s the basement i c e in  a broad s y n c l i n e . In  be  is  m thick,  20 - 90 m  i c e bottom increases by Disraeli Glaciers, a  the  thick.  10 dB  fact  and  for  -which  8  suggests that they are  floating.  2. PROCESSING DIGITAL RADIO ECHO SOUNDING DATA  2.1 INTRODUCTION In t h i s chapter  I d i s c u s s p r o c e s s i n g techniques which can  be a p p l i e d t o d i g i t a l radar easily  identified.  classified  Processing  to  make  objectives  reflections can  be  i n t o three c a t e g o r i e s : ( i ) reducing noise  reflections  clearer;  (increasing sections  data  ( i i ) making  resolution);  indicate  reflectors.  In  the  this  r e d u c t i o n and simple  the  ( i i i ) moving true  thesis  spatial I  limit  broadly to  reflections  make  sharper  reflections  so  relationships discussion  more  that  of the to  noise  r e s o l u t i o n - i n c r e a s i n g techniques.  2.2 RECORDING THE DATA The through then  t r a n s m i t t e d power r e t u r n e d t o the r e c e i v e r i s passed a l o g a r i t h m i c a m p l i f i e r with an 80 dB  sampled  range,  and s t o r e d on f o u r - t r a c k analogue magnetic  (see Table 2.1 f o r system parameters; Narod and C l a r k e  dynamic  1979,  and  1983 d e s c r i b e the UBC 840 MHz radar f u l l y ) .  tape Narod  Various  data a r e s t o r e d on the four t r a c k s : 1.  Channel 1. IRIG time code marking hours, minutes, seconds, and  decimal  seconds. T h i s time  i s d i s p l a y e d on the radar  system c l o c k and can be c o n c u r r e n t l y imprinted photographs  on  aerial  to allow the photographs and radar data to be  accurately correlated. 2.  Channel 2. The a c t u a l radar  data.  3.  Channel 3. S y n c h r o n i z a t i o n code i n d i c a t i n g when the  9  radar  10 Table 2.1 System  System parameters f o r the UBC 840 MHz radar  Performance  1 26  dB  Power output  4. 1  kW  Frequency  840  MHz  10  kHz  50  ns  Pulse r i s e time  18  ns  Pulse f a l l  28  ns  Bandwidth  40  MHz  Dynamic range  80  dB  Recovery from s a t u r a t ion  100  ns  Forward gain  15.5  dB  E-plane beam width (3 dB)  18  deg  H-plane beam width (3 dB)  44  deg  Transmi t t e r :  Repetition Pulse  rate  length  time  Rece i v e r :  Antenna:  Narod and C l a r k e parameters.  (1983) present a f u l l  list  of system  data should be d i g i t i z e d . 4.  Channel 4. Voice  track  for  navigational  and  other  comments. To  sample  the 40 MHz r e c e i v e r bandwidth without a l i a s i n g  r e q u i r e s an 80 MHz sampling frequency.  Low  power,  portable,  11 inexpensive if  field  equipment cannot sample at t h i s  the data c o u l d be sampled at 80 MHz,  difficult avoid  to r e c o r d them completely  this  problem,  the  data  rate.  i t would be  extremely  without p r e - p r o c e s s i n g .  are  sampled by s t r o b i n g  incoming pulses  i n a manner analogous to that used by  oscilloscopes.  The  by t a k i n g only one The  first  complete sounding record sample per  sample  is  radar pulse  taken at  512  points  (5.12  from  MS) or  1024  and  To the  sampling  ( t r a c e ) i s formed  10 ns on the  second at 20 ns on the second p u l s e , either  Even  pulses.  first  pulse,  the  on.  Traces  of  so  points  many  (10.24 <us) can  be  generated. The  radar pulse  repetition  r a t e i s 10 kHz;  t h e r e f o r e at a  10 ns sample s e p a r a t i o n , the apparent sampling r a t e i s 100 while by  the  a c t u a l sampling r a t e i s 10 kHz.  strobing requires  constant 100  ms).  over  the  the  input  time  f a r t h e r along  needed  fading from  to a c q u i r e one is  60 m/s  t r a c e the  i f i t d i d , the radar  relatively trace  and  (50  or  1024-point  (variation  interference will  caused be  in by  i c e does  because over not  filter  the data.  r e f l e c t i o n strength reflector  undersampled,  d i s t r i b u t i o n of r e f l e c t i o n s t r e n g t h s  change  i l l u m i n a t i o n pattern  ( f o o t p r i n t ) would s p a t i a l l y  pattern  inclusions)  be  the data does not cause d i f f i c u l t y  even  the r e f l e c t o r  to  data  first.  the 6 m r e q u i r e d to o b t a i n one and  sample the  taken, the l a s t p o i n t of a t r a c e i s taken 6 m  t r a c k than the  Strobing  much,  waveform  If the a i r c r a f t a i r s p e e d  t r a c e s are being  To  MHz  in  roughness but the  the  on The  resulting and  ice  statistical  fading  pattern  12 will  be c o r r e c t (Narod  does  not  affect  and C l a r k e either  1983).  ice  Hence  thickness  the  or  strobing  reflectivity  computat i o n . The  analogue  magnetic  tapes  l a b o r a t o r y where they are d i g i t i z e d and nine-track  are  returned  the  data  to  stored  the on  computer tape. I add a 52-byte header to each data  t r a c e to s t o r e v a r i o u s t r a c e parameters: the t r a c e number; the number  of  p o i n t s contained  i n the t r a c e ; the IRIG time code;  f l a g s f o r i n c o r r e c t l y d i g i t i z e d t r a c e s and c a l i b r a t i o n t r a c e s ; the and  geographical surface  location;  pulses;  reflections.  These  and  put  a  the  point-number  of  any  visible  headers are updated as the p r o c e s s i n g  i n t e r p r e t a t i o n proceeds. to  the point-number of the transmit  stable  1 MHz  The  radar system a l l o w s the  sawtooth c a l i b r a t i o n - p u l s e  sampler and hence onto the magnetic  tape,  allowing  and  operator into  the  accurate  d e t e r m i n a t i o n of the sampling  time base. Subsequent p r o c e s s i n g  s k i p s f l a g g e d c a l i b r a t i o n and  incorrectly digitized traces.  2.3  PROCESSING TO PRODUCE INTERPRETABLE SECTIONS Radar  sections  (reflections)  and  the image). The as  possible  are noise  images  containing  both  signal  (any unwanted s i g n a l which degrades  p r o c e s s i n g i s a d j u s t e d to reduce noise as much  while m a i n t a i n i n g good r e s o l u t i o n . The  sources:  energy;  r e c e i v e r s a t u r a t i o n ; m u l t i p l e r e f l e c t i o n s from energy reverberates  obscures  hiss;  several  low  times  frequency  has  various  which  tape  noise  between  backscattered  reflectors  deeper r e f l e c t i o n s . By reducing t h i s noise I can  and see  13  the  reflections Noise  in the  and  filtering  signal  applied  reducing the  data more e a s i l y . cannot  to  image  remove  For  spaced,  yet  separated;  f i l t e r s the  example,  if  low-pass f i l t e r i n g ,  i s removed from r e f l e c t i o n s  closely one  by  totally  noise a l s o  resolution.  high-frequency tape h i s s content  be  (SNR)  I  reduce  thus broadening them.  resolvable, reflections  ratio  signal,  high-frequency  and  Two  could merge  into  increases  the  broad r e f l e c t i o n . A good p r o c e s s i n g scheme  signal-to-noise  any  maintains  good  image  resolut ion. I  g e n e r a l l y use  l i n e a r high-pass and  reduce n o i s e . These f i l t e r s must be inexpensive  because  processed. If one set,  more  had  of  the  low-pass f i l t e r s  simple and  l a r g e •number  to  computationally of  p o i n t s to  be  a l a r g e computing budget or a small data  sophisticated  and  expensive  filters  could  be  applied. Occasionally, reflections  easier  low-amplitude the  power  of  noise to  reduction  i d e n t i f y . For  reflections  needs  high-amplitude  r e d u c t i o n ) , I use  alone  does  not  example, i f the to be  power  increased r e l a t i v e  reflections  (dynamic  n o n l i n e a r automatic gain c o n t r o l  because AGC  degrades the  filtering  frequency content of  consists  of  roughly  20  to  range  easier  i s necessary i f AGC  to  i s used  SNR.  Throughout t h i s s e c t i o n the  of  (AGC). With  reduced dynamic range, low-amplitude r e f l e c t i o n s are identify. Careful linear  make  I d i s c u s s in a q u a l i t a t i v e  radar  traces.  A  clear  data  points:  I call  manner  reflection  signals  which  contain  more  than  20 data p o i n t s low  frequency,  which c o n t a i n l e s s than 20 data p o i n t s terminology visualize  i s convenient  the  frequencies  effects cannot  high  the  be  filters.  this  speaking,  separated  reflections  c o n t a i n energy at a l l f r e q u e n c i e s between  and Nyquist  frequencies.  The radar 1.  preliminary processing  I can apply  because the  DC  to enhance a  s e c t i o n are as f o l l o w s :  Stacking. across least  2.  steps  This  to more e a s i l y  Strictly  easily  signals  frequency.  because i t allows one  of  and  T h i s i s a t r a c e - t o - t r a c e moving average a p p l i e d  the s e c t i o n . R e f l e c t i o n s s e v e r a l t r a c e s and  High-pass  are  coherent  across  at  are t h e r e f o r e emphasized.  filtering.  This  is  used  remove  the  roughness and  ice  high-pass f i l t e r  used  low-frequency noise caused by r e f l e c t o r  to  inclusions. 3.  Differentiating. to convert  T h i s i s a vigourous  leading  edges  s p i k e s which p r e c i s e l y 4.  Automatic small and small  5.  gain  of  l o c a t e the  control.  are  visible  r e l a t i v e l y more than l a r g e  Low-pass  filtering.  content  are  reduces t r a c e dynamic range;  made  This  into  onsets.  amplified  high-frequency  (onsets)  T h i s i s used i f r e f l e c t i o n s  b a r e l y v i s i b l e . AGC  reflections  reflections  is  they  are  reflections.  used  which both AGC  because  to and  reduce  the  differentiating  emphasize. Unless  AGC  is  i r r e l e v a n t . -Because AGC  used,  the  i s nonlinear,  processing different  sequence results  is are  15 obtained  if  changed;  the  any  i f AGC i s not used. In the s e c t i o n on AGC I  order  i t s position other  in  filters  the  processing  sequence  is  are l i n e a r and can be a p p l i e d i n discuss  where t h i s o p e r a t i o n should be a p p l i e d . A f t e r p r o c e s s i n g , the data are ready have  five  display  reflection  options:  shape  (ii) variable  or  area  ( i ) A-scope  be  plotted.  f o r examination  quality-control  monitor  ( i i i ) g r e y - s c a l e as  interpretation  section;  reflections  good  (iv) threshold  data;  s t r e n g t h of r e f l e c t i o n s  the  (v) c o l o u r  general to  level  I of  sections;  (A-scope with p o s i t i v e peaks f i l l e d  locate r e f l e c t i o n s ;  in  to  i n ) to purpose  show to  large  show  the  in a section.  2.3.1 STACKING Because  of  the  trace  overlap  introduced by the radar  f o o t p r i n t and slowly v a r y i n g i c e changes, two adjacent should  be  similar  moving average noise  and  except  (stacking)  emphasizes  reflections),  a p p l i e d a c r o s s the flat-lying  the  moving  maintain  across  added n o i s e . Applying a  the  section  reduces  Stacking does not reduce  the  section  ( f o r example,  because s t a c k i n g i s a low-pass Stacking  have  this  large  is  filter  effective  because  low-frequency  content  r e f l e c t i o n s do not stack w e l l . The width of  average  good l a t e r a l  reduce noise  across  section.  reflections  l a t e r a l l y . Dipping  the  reflections.  noise which i s coherent multiple  for  traces  (stack  fold)  can be a d j u s t e d to e i t h e r  r e s o l u t i o n (small stack f o l d ) or g r e a t l y  ( l a r g e stack  fold).  16 Analogue Z-scope r e c o r d i n g s are o f t e n p r i n t e d with t r a c e s overlapped, (Evans  resulting  and  Smith  i n an i n t e g r a t i o n on the r e c o r d i n g  1969).  I  call  my moving average a stack  rather than an i n t e g r a t i o n because of i t s seismic  stack  where  traces  with  a  d i f f e r e n t added noise are averaged traces  can  be  aircraft a  on  similarity  to the  common true s i g n a l but  together.  Adjacent  filtered  a reflector  by the radar f o o t p r i n t . The  aircraft  speed,  the  15-fold i s o f t e n  SNR  r a t e , and  one radar f o o t p r i n t o v e r l a p s 60 m  along t r a c k , comparable to s p a t i a l l y Increasing  by  f i l t e r i n g over  widening  unproductive  11 t r a c e s .  the stack beyond about  because  the  section  becomes  e x c e s s i v e l y f i l t e r e d . For example, an n - f o l d stack w i l l the amplitude amplitude  of Gaussian  of  any  dipping  and  noise by /n",  reflections  t r a c e s . Stacks wider than  radar  i s an 18° x 44° e l l i p s e . At a 200 m  t e r r a i n c l e a r a n c e , a 10 t r a c e / s a c q u i s i t i o n  60 m/s  radar  c o n s i d e r e d to c o n t a i n a common s i g n a l because  they are s p a t i a l l y footprint  film  but  coherent  also  over  reduce  reduce fewer  the  than n  15-fold i n c r e a s e the SNR by removing  laterally-short  reflections.  To  locate  deep  r e f l e c t o r s the stack f o l d can be i n c r e a s e d because geometrical spreading  i n c r e a s e s the radar  footprint.  S e l e c t i n g the stack f o l d depends upon what one emphasize:  unstacked  data stacked over but broad  does  most  to  c l e a r l y shows d i f f r a c t i o n s ;  l e s s than one radar f o o t p r i n t  reduces  noise  not broaden r e f l e c t i o n s ; h e a v i l y stacked data g i v e s  averages  generally  data  wants  use  or  emphasizes  9-fold  stacks  weak because  horizontal this  layers.  width  I  does not  17 spatially  filter  the  s e c t i o n e x c e s s i v e l y , yet s u b s t a n t i a l l y  reduces the n o i s e . The low-pass f i l t e r i n g can  caused  by  stacking  be observed i n F i g u r e 2.1.  unstacked  Figure  2.1  As  9-fold  25-fold  101-fold  Stacking.  the stack  fold  increases,  both  the noise  and the r e s o l u t i o n decrease.  If the r e f l e c t o r of i n t e r e s t i s s t e e p l y aircraft  or the  range i s r a p i d l y changing, a l i g n i n g the r e f l e c t i o n of  interest  before  removes  lateral  filtering  dipping  stacking  can  high-frequency  be  advantageous.  content;  thus  Alignment the  spatial  r e s u l t i n g from s t a c k i n g does not s e v e r e l y a f f e c t the  reflection.  For  my  necessary i f the stack  data fold  this  alignment  i s kept small  i s g e n e r a l l y not  (<15).  18  2.3.2 The longer  HIGH-PASS FILTERING rate  at  which  the power decays a f t e r the pulse no  i l l u m i n a t e s the r e f l e c t o r  i s known as the fading  t h i s rate i s a f u n c t i o n of the r e f l e c t o r  roughness. The  i n t r o d u c e s low-frequency content i n t o the data reduced from  by a  rate;  which  fading can  be  high-pass f i l t e r i n g . Removing low-frequency noise section  occasionally  simplifies  enhances  reflection  obscured  by  b a c k s c a t t e r e d energy, and a l l o w s the use of v a r i a b l e area  and  threshold p l o t t i n g  small  identification,  formats.  To high-pass f i l t e r moving  average  reflections  over  the data I f i r s t  a  smooth them  inexpensive  and  works  both  sides  of large r e f l e c t i o n s . These  small r e f l e c t i o n s , but adjusted  to  superimposed (Figure  2.3.3  the  minimize  averaging the  on b a c k s c a t t e r e d  window  width  width  Small  high-pass  can  be  reflections filter  well  DIFFERENTIATING i s a v i g o r o u s high-pass f i l t e r  l o c a t i n g r e f l e c t i o n onsets. In are  differentiating are  well. It  2.2).  Differentiating  (<400 m)  energy  is  lobes can obscure  window  effect.  filter  moderately  causes negative lobes of one-half the averaging on  a  s p e c i f i e d time window, then s u b t r a c t  t h i s smoothed v e r s i o n from the o r i g i n a l d a t a . T h i s computationally  with  somewhat  generally  my  data  characterized  shallow  useful for reflections  by sharp onsets which  turns i n t o s p i k e s . Deeper r e f l e c t i o n s broadened  (>400 m)  by n o i s e , making d i f f e r e n t i a t i n g  less  19  I  1  unfiltered  Figure  2.2  High-pass  2.0  I  us  1 -° l  1.0 us  0.4  us  filtering.  The u n f i l t e r e d t r a c e was f i r s t 9 - f o l d stacked. The time underneath the t r a c e i s the w i d t h of the moving a v e r a g e used to p r o d u c e the smoothed t r a c e which i s s u b s e q u e n t l y s u b t r a c t e d from the o r i g i n a l trace.  e f f e c t i v e although i t s t i l l  works.  I d i f f e r e n t i a t e by c o n v o l v i n g Scaling  i s unimportant because the  to show r e f l e c t i o n l o c a t i o n s , and indication  of  high-frequency low-frequency the  filter  Fourier  (1,0,-1)  The  DC  of  i s being processed  returned  power. D i f f e r e n t i a t i n g increases  the  content  of  the  content;  this  is  a  the  component  derivative  trace  e f f e c t can  is  relative be seen by  transfer  to  examining  function  s t r a i g h t l i n e with u n i t y slope  through the o r i g i n ( A ( u ) = -ico; A(CJ) component  data.  an  a  the  the  not  t r a n s f e r f u n c t i o n . The  domain  section  with  i s ' the  complex  in  the  passing Fourier  t r a n s f e r f u n c t i o n at angular frequency CJ) . (w=0)  is  eliminated;  the  low-frequency  20 content  (|w|<1)) i s reduced; and  the  high-frequency  content  (|GJ|>1) i s i n c r e a s e d . The SNR at high f r e q u e n c i e s i s g e n e r a l l y low,  so  (Figure  differentiating 2.3)  which  can  emphasizes  high-frequency  subsequently  be reduced  noise  by low-pass  filtering.  unfiltered  Figure  2.3  The  differentiated  Differentiating.  unfiltered  t r a c e was f i r s t  9-fold  stacked.  2.3.4 AUTOMATIC GAIN CONTROL Set t o FM r e c o r d i n g a t 15 i p s (38.1 cm/s), the SNR of the Racal The 250  tape  recorder  i s 48 dB (Racal T e c h n i c a l Handbook  maximum v o l t a g e that can be recorded times  above  the  -48 dB  noise  1978).  (0 dB l e v e l ) w i l l  be  l e v e l . I f I p l o t a 0 dB  s i g n a l at a 1 cm d e f l e c t i o n , a -48 dB s i g n a l w i l l  produce  an  21 unobservable 0.004 cm d e f l e c t i o n . C l e a r l y must  the  dynamic  range  be reduced i f a l l r e f l e c t i o n s a r e t o be seen on the same  section. Automatic  gain  control  generate a t r a c e c o n t a i n i n g or  absolute  this  value  and  reduces dynamic range. I  e i t h e r the root mean squared  of the t r a c e being  positive-valued  averages,  (AGC)  gain  finally  trace  divide  processed, then smooth  with  the  (RMS)  one  or  original  two  trace  moving by  the  smoothed gain  t r a c e . The width of the moving-average window i s  adjusted  give the d e s i r e d dynamic range r e d u c t i o n .  to  smoothed average i s s m a l l , large;  i f the  normalization and  smoothed  the average  Watts and Wright their  is  large,  (1981) a p p l i e d time-varying  Columbia  occur  the  Glacier  data  to  my  near  AGC,  resulting  the  trace  beginning  I  use  gain  amplify small  are  Although t h e i r TVG does not s u f f e r from some of of  is  (Figure 2.4).  l a t e - o c c u r r i n g r e f l e c t i o n s . With t h e i r TVG which  normalization  i s s m a l l . Consequently, l a r g e peaks are reduced,  small peaks are a m p l i f i e d  to  resulting  If the  (TVG) small,  reflections  not a m p l i f i e d . the  problems  the AGC because i t i s e f f e c t i v e over the  entire trace. The  major  problem  o c c u r r i n g near a l a r g e amplified  i f the  r e f l e c t i o n overlaps zones"  of  one-half  with one  smoothing  AGC i s that a small  will  be  window  decreased centred  the l a r g e . The l a r g e window  width  on  r e f l e c t i o n s . Noise trapped between two  power either  reflection  rather  than  the  small  on  causes  "dead  s i d e of l a r g e  reflections  separated  22  unfiltered  Figure  2.4  Automatic  2.0 us  1.0 us  0.4 us  gain control.  The u n f i l t e r e d t r a c e was f i r s t 9-fold stacked. then using a 0.10>s window. T h e t i m e u n d e r n e a t h t h e t r a c e moving a v e r a g e u s e d t o smooth t h e g a i n t r a c e .  by s l i g h t l y more than one window width reflections  because  of  the  can  faint  seen,  but  AGC  should  be  often  tried,  at  one-half  as  i t . On  r e f l e c t i o n s can be always  AGC-induced a r t i f a c t s can be i d e n t i f i e d because follows,  appear  dead zones which bracket  s e c t i o n s where no r e f l e c t i o n s or only the  high-pass filtered i s the width of the  cautiously. the  artifact  the window width, the r e f l e c t i o n which  causes i t . The  AGC  i s n o n l i n e a r and hence c o n t r o l s the p r o c e s s i n g  flow. Low f r e q u e n c i e s I  i n t e r f e r e with the a c t i o n of the AGC  g e n e r a l l y high-pass f i l t e r  AGC emphasizes high-frequency suppressed  noise,  so  the data beforehand. Because the noise and re-enhances p r e v i o u s l y  I low-pass f i l t e r  a f t e r AGC. S t a c k i n g  isa  23 form  of  low-pass  filtering  but must be performed before AGC  because the assumption u n d e r l y i n g s t a c k i n g i s that  the  data  c o n t a i n a common s i g n a l plus added n o i s e ; AGC m o d i f i e s a t r a c e using only information contained  in  that  individual  thus t r a c e s may no longer c o n t a i n a common  2.3.5  signal.  LOW-PASS FILTERING  Low-pass  filtering  reduces  the high-frequency  emphasized by the AGC and d i f f e r e n t i a t i o n . I by  applying  a  moving  triangular  waveform;  the data with a  see  Kanasewich  Bartlett  remove  high-frequency  content  filter  a l l  inexpensive  high-frequency  i s needed  window  (a  1975, p. 109). I use a  B a r t l e t t window because i t i s computationally not  low-pass  noise  average twice down the t r a c e . T h i s i s  e q u i v a l e n t to c o n v o l v i n g  does  trace,  to  content.  maintain  good  and Some image  resolut ion. S e c t i o n s which have not been d i f f e r e n t i a t e d or gain  controlled  Excessive  generally  low-pass f i l t e r i n g  do  not  need low-pass  filtering.  decreases the image r e s o l u t i o n by  broadening r e f l e c t i o n s , or blending c l o s e l y spaced together  automatic  reflections  (Figure 2.5).  2.3.6  DISPLAY  S e c t i o n s are p l o t t e d with increasing  the  reflection  arrival  time  v e r t i c a l l y downwards to a maximum of 10.24 jus, and  the t r a c e a c q u i s i t i o n time i n c r e a s i n g h o r i z o n t a l l y . I can p l o t a s e c t i o n f i v e ways ( F i g u r e s 2.6, 2.7, and 2.8):  24  unfiltered  igure  2.5  Low-pass  0.03  us  0.09  us  0.25  us  filtering.  The unfiltered t r a c e i s t h e 1 .0„s AGC time underneath the t r a c e i s the width f i l t e r the t r a c e .  A-scope (Figure 2.6a).  t r a c e from F i g u r e Bartlett window  h o r i z o n t a l l y , the r e t u r n time v e r t i c a l l y . A-scope  sections  to p l o t and  power  The to  plotted  inexpensive  returning  2.4. used  is  are  The  filtered of the  work w e l l on unprocessed  as a v i s u a l check on data q u a l i t y . Sparse A-scope often  provide  reflections;  a  the  means gaps  of  between  initially traces  can  data  sections  identifying be f i l l e d  by  examining more densely or d i f f e r e n t l y p l o t t e d s e c t i o n s . V a r i a b l e area with  the  (Figure 2.6b). A-scope  positive  peaks  shaded  format emphasizes r e f l e c t i o n s and to  correlate  pulse  traces in.  allows  The  are  plotted  variable  the  shape in a d d i t i o n to pulse  area  interpreter amplitude.  V a r i a b l e area p l o t t i n g does not work w e l l i f the data have  25 a DC b i a s or much low-frequency content; the data must first  d i f f e r e n t i a t e d or high-pass f i l t e r e d .  I f the dynamic  range i s l a r g e I can AGC the data or p l o t them with amplitude  peaks  overlapped,  to  amplitude peaks. T h i s format  would  acquired  echo  returned  by  impulse  radio  s i g n a l amplitude  returned  signal  and  power)  correlated  across  the  strength.  Variable  phase  well  in  i s my  large smaller  f o r data  which  (rather  signal  section  the  sounders  because  area  observe work  be  record  than  phase  addition  c o u l d be to  preferred  only  signal  format  for  p l o t t i n g d i f f e r e n t i a t e d data. 3.  Threshold  (Figure 2.6c). Data values  t h r e s h o l d a r e connected by v e r t i c a l the  threshold  remain  f o r pen  segments, v a l u e s  unconnected. Threshold  economical on dot matrix or unsuitable  above a p r e - s e l e c t e d  electrostatic  plotters  can  data  with  be a d j u s t e d  Threshold  2.6  c)  so  often.  to make  reflections  stand  out  (overleaf)  On  clearly.  p l o t s are v i s u a l l y s t r i k i n g ; u n f o r t u n a t e l y  A-scope,  The s e c t i o n i s f r o m t h e transmit pulse arrives bottom reflection at r e f l e c t i o n s (see Figure a) b)  p l o t t e r s , but  c l e a r r e f l e c t i o n s the p l o t t i n g t h r e s h o l d  format i s s e n s i t i v e to t h r e s h o l d  Figure  plotting is  because so many t r a c e s are  p l o t t e d and the pen i s l i f t e d and s e t down good  below  v a r i a b l e area,  selection  and t h r e s h o l d  and  does  displays.  M i l n e I c e S h e l f ( s e e F i g u r e s 4.12 and 4.13). The a t 0.25,,s, t h e s u r f a c e r e f l e c t i o n a t 1 . 0 | / S , a n d t h e 2.0»,s. Reflections below 2.0„s are multiple 3 . 2 ) . E a c h s e c t i o n was p r o c e s s e d d i f f e r e n t l y :  A - s c o p e . 9 - f o l d s t a c k e d . E v e r y 100th t r a c e p l o t t e d . V a r i a b l e area. 9-fold stacked, then high-pass f i l t e r e d . Every 25th t r a c e plotted. Threshold. 9-fold stacked, h i g h - p a s s f i l t e r e d , t h e n p l o t t e d w i t h a 5% t h r e s h o l d ( r e l a t i v e t o t h e maximum a m p l i t u d e ) . Every 5th trace p l o t t e d .  this not  t w o - w a y t i m e (us)  t w o - w a y t i m e (us)  t w o - w a y time  (us)  27 show any 4.  Grey and  r e f l e c t i o n s below the  scale.  The  threshold.  r e t u r n i n g power i s assigned  p l o t t e d in a manner analogous to Z-scope  grey-scale levels,  plot  but  Versatec  is  the  reflections  the  allows  threshold  512  p o i n t s / t r a c e v e r t i c a l l y on  resolution  needed  to  which  generate  11  the  high-pass  to reduce any  gain c o n t r o l l e d the  like  selected  reduced  a  either  example see Figure (Figure  2.7).  me  have  l a r g e DC  not  plot.  The  emphasize  grey small a  has  a  to p l o t up  to  (4  dots/point Grey-scale  been  lightly  b i a s . Automatic  grey-scale  plot  grey  levels  well  scale  is  can  be  r e f l e c t i o n locations (for  4.13), or show the true returned  Grey  A  dynamic range causes the s e c t i o n to  threshold  to  do  see  plotter  scale).  s e c t i o n s which  sections  to  inch paper grey  on  filtered  sections.  might cut o f f . I use  allows  p l o t t i n g works best  because  one  electrostatic plotter: this  dot/inch  are  level  t h r e s h o l d p l o t with m u l t i p l e  grey-scale  which  V-80  a  200  look  a grey  my  preferred  power  format f o r  p l o t t i n g u n d i f f e r e n t i a t e d data. 5.  Colour  level  (Figure  2.8).  power l e v e l . S p e c i a l i z e d  Figure  2.7  (overleaf)  Grey-scale  A colour  image  i s assigned  processing  to each  equipment  display.  The section is f r o m t h e M i l n e I c e S h e l f ( s e e F i g u r e s 4.12 and 4 . 1 3 ) . A l l system, geometrical s p r e a d i n g , and p r o p a g a t i o n losses have been removed assuming a p r o p a g a t i o n l o s s r a t e o f 0.04 dE/m. O n l y t h e PRC r e m a i n s and i s d i s p l a y e d a s a g r e y l e v e l . The w h i t e p i x e l s a t a p p r o x i m a t e l y 1.8j,s i d e n t i f y the bottom r e f l e c t i o n onset.  is  28  r e f l e c t i o n s t r e n g t h (dB)  o CM I  O  CO I  o  o  10  I  o  o  I  l  I  I I I I I I I I I I I I I I  I I I I I  T  I I I I  CM  (Sn) dUJIl |©ABJi  A B M - O M I  I I  i—r  co  29 needed  to  journals,  produce  these  i f possible,  sections,  i s generally  s e c t i o n s are p a r t i c u l a r l y u s e f u l  costly.  i f the data are  c o e f f i c i e n t f o r example). I t i s much e a s i e r  grey-scale  useful  than  reflections in returned  2.8  section.  (overleaf)  ice  (power to on  C o l o u r - l e v e l s e c t i o n s are no more sections  because r e f l e c t i o n s are  Colour  the  on a c o l o u r - l e v e l s e c t i o n than  grey-scale  power rather  of  processed  reflection  the value of a point  property  in  Colour-level  some  a  Figure  reproduction  to r e f l e c t  see  physical  and  for  identifying  i d e n t i f i e d by changes  than magnitude.  reflectivity  display.  The s e c t i o n i s f r o m t h e M i l n e I c e S h e l f ( s e e F i g u r e s 4.12 and 4.13). All system, geometrical spreading, and p r o p a g a t i o n l o s s e s have been removed a s s u m i n g a p r o p a g a t i o n l o s s r a t e o f 0.04 dB/nt. O n l y t h e PRC r e m a i n s and is displayed as a colour level. The black p i x e l s a t a p p r o x i m a t e l y 1 . 8,,s I d e n t i f y the bottom r e f l e c t i o n onset.  3.  3.1  INTERPRETING A DIGITAL RADAR SECTION  INTRODUCTION An  interpreter  stops  clear  r e f l e c t i o n s are  will  ever  the  be.  radar s e c t i o n  calculating located the  By  r e p r o c e s s i n g a radar s e c t i o n  obtained, or  interpreting and  and  The  " a r t " of  thesis.  locating  straightforward; practice.  in  possibly these  (PRC)  and  (LR). i s beyond the  reflections  locating  none  from  coefficient  reflections  Locating  then  characteristics  r e f l e c t i o n s : power r e f l e c t i o n  that  reflections  t h e i r depth,  ice  i c e propagation l o s s rate  this  I mean l o c a t i n g  calculating  reflector  i t becomes c l e a r  once  in  reflections  In t h i s chapter I f i r s t  scope  of  data  is  good  in  poor  data  takes  d i s c u s s some problems which  make r e f l e c t i o n s d i f f i c u l t  to  how  I  calculate  power r e f l e c t i o n c o e f f i c i e n t s ,  and  ice  thickness,  locate,  propagation l o s s r a t e s for the and  others  (1969)  discuss  UBC  the  840  then  MHz  discuss  radar  interpretation  data.  Robin  of r a d i o  echo  sounding data in d e t a i l .  3.2  LOCATING REFLECTIONS Once the  onset  times  l i n e s are driving  with  an  the  are  digitizer number  located  e r a s a b l e crayon. The  then d i g i t i z e d on  number/point locations  r e f l e c t i o n s have been  an  returns  pairs.  x-y the  Points  l i n e a r l y interpolated  31  I  colour  locations  digitizer; x-y  the  their  of  program  c o o r d i n a t e s as  between  the  these  trace  digitized  to serve as a guide for a  32 computer  program  locations. data  The  which  automatically  computer  amplitude  or  the i n t e r p o l a t e d  maximum  slope.  The  maximum i s the new l o c a t i o n and i s s t o r e d i n header. for  I  use  tunes"  point  the  trace  the maximum slope t o l o c a t e r e f l e c t i o n  onsets  maxima  f o r PRC  c a l c u l a t i o n s . The transmit pulse and located;  of the  data  reflection  always  f o r the  location  i c e t h i c k n e s s c a l c u l a t i o n s , and the maximum  locate  these  program f i n e tunes by s e a r c h i n g the  i n a window surrounding  maximum  "fine  the  bottom  and  and  amplitude  propagation  surface  internal  to loss  reflection  are  reflections  are  l o c a t e d where v i s i b l e . I  have  reflections  developed across  a  algorithms section.  which a u t o m a t i c a l l y t r a c k  These  r e f l e c t i o n p o s i t i o n from the p r e v i o u s search  f o r the  maximum  amplitude  algorithms  use  the  t r a c e as the c e n t r e of a  or  slope  in  the  search  window. C o n s t r a i n i n g the d i f f e r e n c e between l o c a t e d - r e f l e c t i o n positions  on  adjacent  fading-induced  "jitter"  works  well  algorithms  on  clear  are  needed  traces  points  reduces  i n the l o c a t i o n . T h i s simple  algorithm  horizontal to  to  1-3  reflections;  reliably  more  robust  l o c a t e d i p p i n g or f a i n t  r e f l e c t ions.  3.2.1  EFFECTS WHICH OBSCURE REFLECTIONS  Three types of e f f e c t s can obscure  reflections:  1.  System e f f e c t s caused by l i m i t a t i o n s of the radar  2.  Artifacts  introduced by the p r o c e s s i n g .  3.  Physical  effects  associated  with  the  system.  physics  of  33 electromagnetic wave propagation The  major  system  effect  r e c e i v e r dead time  caused  penetration  the  where  of  by  through i c e . the UBC 840 MHz radar i s  clipping.  To  obtain  maximum  i c e i s e i t h e r deep or l o s s y ,  aircraft  t e r r a i n c l e a r a n c e i s kept low; t h i s p r o x i m i t y returning 230  ns  power  to  f o r the  faithfully  saturate  system  record  to  the data  data have been c l i p p e d  can  cause  the r e c e i v e r . I t takes recover  from  the  roughly  saturation  and  (Narod and C l a r k e 1983). Once the  and  recorded  there  is  little  that  subsequent p r o c e s s i n g can do to recover the l o s t i n f o r m a t i o n . Processing a section n e c e s s a r i l y good  processing  reflection  scheme  locations  maximizes  can  be  introduces a r t i f a c t s . the  located  ease  with which the  while  minimizing  p r o c e s s i n g a r t i f a c t s . S e c t i o n s with only f a i n t h e a v i l y processed to causes of  processing  make  them  visible;  A  the  r e f l e c t i o n s are  occasionally  this  a r t i f a c t s t o appear as r e f l e c t i o n s because  the absence of true r e f l e c t i o n s . Both  high-pass  filters  and  AGC  surrounding l a r g e r e f l e c t i o n s . These obscure zones  reflections, to  appear  unprocessed  as  dead  "dead  zones  zones"  can  either  or cause n o i s e trapped between two dead a  reflection.  A-scope , s e c t i o n s  the  which r e f l e c t i o n s are r e a l , then densely-plotted  cause  processed  From  sparsely-plotted  i n t e r p r e t e r can determine  find  these  sections  and  reflections continue  in the  i n t e r p r e t a t i o n between the A-scope t r a c e s . Various  physical  locate: c r i t i c a l  effects  make r e f l e c t i o n s d i f f i c u l t to  r e f r a c t i o n at the i c e / a i r  interface,  dipping  34 reflectors,  diffractions,  focussing  undulating  reflectors,  from v a l l e y  w a l l s . These e f f e c t s are  and  m u l t i p l e r e f l e c t i o n s , and the  two  storage of  methods  and  of  1970  (see  incidence  greater  or  for example  reflections For  errors  34°.  a l l the  occur. For  dipping  less  a coincident  reflector  ( t h i s i s only s t r i c t l y  r e f l e c t o r s ) . For i s not  than  can  a dipping  energy  true for  come  from  reflector  (time s e c t i o n s d i s p l a y  reflector  depth),  but  others  r e f l e c t i o n , occurs a i r at  is  can  steeply  d i r e c t l y underneath the  time s e c t i o n  and  angles  transmitted  be  observed.  than 34°,  timing  receiver  pair,  must have been normally i n c i d e n t  energy  outline  discussion).  t r a n s m i t t e r and  reflections  backscattered  and  energy r e f l e c t s downward. Hence  received  point  Robin  from slopes g r e a t e r than 34°  reflectors  sampling  i c e to the  No  and  geometry  I w i l l give a b r i e f  total internal  than  interface,  data  for a more d e t a i l e d  refraction,  reflections  p h y s i c s and  only  rays t r a v e l l i n g upwards from the  through the no  different.  effects  Harrison  Critical for  identical;  techniques are  these p h y s i c a l  1969,  are  by  same for d i g i t a l  analogue r a d i o echo soundings because the of the  defocussing  smooth any  the  on  the  reflectors;  point  on  normally  rough incident  antenna as d i s p l a y e d on pulse r e t u r n  actually  time  a  rather  a p o i n t up-dip from  the  entire  aid  nadi r . Removing interpretation "migrated" As  well,  this  effect  is called  from  migration  an  because  to t h e i r true s p a t i a l r e l a t i o n s h i p  migration "collapses"  section  to  reflections in the  are  section.  d i f f r a c t i o n hyperbolae i n t o  the  35 scattering-points presented  a  which  produced  the  located  and  reflections  method moves only does  Occasionally  deconvolution i n d u s t r y the migration;  which  not  Harrison's  is  term  by  the  considered a is  industry  sounding source from a seismic t r a c e ; assumed  to  result  with the  reflectivity  Migration caused  by  (Figure 3.1)  and  can  discontinuities. blend  difficult  to  true  identify.  focussing e f f e c t s Two  locating  reflections The  the  of  the  trace  is  source wavelet  and  and  small  types of m u l t i p l e r e f l e c t i o n s  undulations. discontinuities these  d i f f r a c t i o n patterns the  radar UBC  effects  identifying  making  unimportant f o r the  denote  focussing  with  O c c a s i o n a l l y though, the  with  of  earth.  associated  in  form  recorded  discontinuities  aid  seismic  effect  c o n v o l u t i o n of the  are  radar  deconvolution  the  reduces d i f f r a c t i o n and  patterns  to  of  called  simple  type of  the  s t r u c t u r e of the  reflector  Diffraction  can  from the  also  entire is  used  removes  true  profiles  method  deconvolution  seismic  the  somewhat u n f o r t u n a t e : in the  technique would be the  (1970)  to t h e i r  migrate the  mathematical i n v e r s e of c o n v o l u t i o n . One used  Harrison  method to move l o c a t e d r e f l e c t i o n s  spatial relationship;  section.  them.  footprint  840  can  reflections  MHz  makes  radar.  confuse a  section:  a i r c r a f t m u l t i p l e s for which energy r e v e r b e r a t e s two  or  times  internal  between  multiples  for  reflectors obscure true  a  reflector  which  (Figure  and  energy 3.2).  reflections.  the  a i r c r a f t , and  reverberates These  Multiple  multiple  between  more  two  ice  reflections  can  reflections  are  easily  36  Figure  3.1  The a) b) c) d)  Diffraction  heavy  lines  are  patterns. expected  diffractions  bottom c r e v a s s e , surface crevasse, unsoundable block, perhaps caused step decrease in ice thickness.  The  shaded  portion  i s impenetrable  aircraft Figure  3.2  Multiple  from:  by  brine  Ice,  rock,  infiltration,  or  water.  Internal reflections.  T is the transmit pulse, S Is the s u r f a c e r e f l e c t i o n , B i s the bottom r e f l e c t i o n . M1, M2, a n d M3, are the first, second, and third multiple reflections. Energy is lost not only through increased geometrical s p r e a d i n g and s c a t t e r i n g , but a l s o p e n e t r a t i o n t h r o u g h the reflector.  i d e n t i f i e d because  the  time  difference  between  f i r s t m u l t i p l e (or between the n and  the n+1  lower  reflection  and  order  multiples),  i s e x a c t l y the same as the time d i f f e r e n c e between  37 the two  r e f l e c t o r s which produced  the m u l t i p l e s .  R e f l e c t i o n s from v a l l e y w a l l s occur i n f r e q u e n t l y with the UBC  840 MHz  valley  radar because of the small radar  wall  reflections  do  occur  they  footprint. are u s u a l l y  When easily  i d e n t i f i e d because they change r a p i d l y compared to r e f l e c t i o n s from the i c e bottom.  3.3  ICE THICKNESS AND The  i c e depth  LAYER SEPARATION  to a r e f l e c t o r i s  z = c (t -t )/2 i  r  (3.1)  s  where z  = depth  in m  c^ = i c e r a d i o wave v e l o c i t y t  i n UI/MS  = time of s u r f a c e r e f l e c t i o n  t  = time of r e f l e c t i o n  i n MS  i n MS  "V*  The the  accuracy of the t h i c k n e s s map n a v i g a t i o n a l accuracy  r a d i o wave v e l o c i t y used accuracy  produced  will  depend  upon  ( v a r i a b l e ) , the accuracy of the i c e (several  percent  of the i d e n t i f i e d r e f l e c t i o n  error),  locations  and  ( l e s s than  the 1%  e r r o r on A-scope t r a c e s ) . Timing  accuracy  (how  i n the time  section)  depends  sounding  pulse.  The  UBC  accurately a reflection upon  840 MHz  the  rise  i s located  time  of  the  radar uses a pulse with an  18 ns r i s e time. T h i s pulse i s sampled every  10 ns; one  sample  38 (approximately estimate velocity in  of  one-half the  the  timing  rise  accuracy.  i s c ^ / 2 ) , t h i s corresponds  locating  the r e f l e c t o r . The  not known t h i s a c c u r a t e l y , and (absolute  range  c o r r e c t i o n used  accuracy)  through  thus timing  accuracy  is  The  absolute  r e l a t i v e range accuracy  a  reasonable  C^=170 m/jus (two-way  At  to a 0.85  the t r u e depth  m range accuracy  the  greater range  in i c e i s  to the  depends upon the  ( t h i s c o r r e c t i o n compensates  velocity  accuracy.  is  r a d i o wave v e l o c i t y  also  propagation  is  time)  for  reflector firn-layer  the  higher  o v e r l y i n g snow and than  the  accuracy  is theoretically  o p t i m i s t i c because noise decreases  firn);  absolute  range  i s about ±10 m. 0.85  m;  this  The  estimate  the accuracy with which  a r e f l e c t i o n can be l o c a t e d . The  ability  upon the sounding less  than  to r e s o l v e c l o s e l y  spaced  pulse l e n g t h . Two  reflectors  one-half  r e f l e c t i o n s . The UBC (this  includes  pulse  length  840 MHz  the  rise  will  r e f l e c t o r s depends  return  radar uses a 90 ns and  fall  separated  by  overlapped  pulse  length  times; Narod and C l a r k e  1983); t h e o r e t i c a l l y the radar should r e s o l v e l a y e r s separated by  only  7m.  t h i n s to 0 m; 10 - 15m  I  have  visible  because  layer  separation  b a c k s c a t t e r e d energy  p u l s e . C l o s e l y spaced overlapped  examined radar s e c t i o n s where the i c e  l a y e r s can  r e f l e c t i o n appears  where the i c e i s t h i n n i n g or  is  lost  at  about  broadens the returned  sometimes be r e s o l v e d i f  the  u n u s u a l l y broad. T h i s works best thickening  r e f l e c t i o n s can be seen to merge.  and  the  individual  39 3.4 REFLECTION AND PROPAGATION LOSSES The r e t u r n e d power measured at the r e c e i v e r output i s the transmitted radar  power  and  spreading,  less  a l l losses:  sampler,  loss  loss  reflection,  by  through  system l o s s e s from the  radio  wave  geometrical  l o s s from s c a t t e r i n g by i c e  i n c l u s i o n s and roughness, and l o s s from d i e l e c t r i c during  propagation  constant  and  determined;  through  geometrical in  the  i c e . The  spreading  space  that  (i.e., A  system can  loss  always  i c e has  the  I  make  the  magnetic p e r m e a b i l i t y of free  i s non-magnetic).  reflecting  surface  causes l o s s e s i n two ways:  first, instead  r e f l e c t e d ; and second, r e f l e c t o r roughness can s c a t t e r the  i n c i d e n t energy thus d e c r e a s i n g the returned power. The reflection  coefficient  (and returned) includes  power  components  r e f l e c t o r , and from The dielectric loss  be  reasonable  some of the energy i s t r a n s m i t t e d through the surface of  is  some i n s t a n c e s the r e f l e c t i o n and propagation  l o s s e s can be measured. In a l l cases assumption  loss  attenuation  from  (PRC) to  from  the the  is  power  the r a t i o of the r e f l e c t e d  incident  power  permittivity  ( i n dB). I t c o n t r a s t a t the  roughness.  propagation  loss  also  has  l o s s through ohmic h e a t i n g and  two  components:  absorption;  and  a a  s c a t t e r i n g by i c e i n c l u s i o n s . The ohmic h e a t i n g i s  caused by i c e c o n d u c t i v i t y and can be c a l c u l a t e d from the i c e l o s s tangent.  40 3.4.1 POWER REFLECTION An  electromagnetic  separating  and  separates  media  partly  impinging  transmitted.  with  on  an  If  a  smooth  relative permittivities  electromagnetic  (Stratton  wave  interface  media of d i f f e r e n t d i e l e c t r i c p r o p e r t i e s i s p a r t l y  reflected  the  COEFFICIENT  wave  is  normally  interface  e, and e  2r  incident,  and then  1941)  R = (/77-/i~;)/(/77+/77)  (3.2)  where R = reflection coefficient e,= p e r m i t t i v i t y  of the media c o n t a i n i n g the i n c i d e n t  e = permittivity  of the media c o n t a i n i n g  2  the  wave  transmitted  wave  The PRC i s d e f i n e d as  PRC = 10•log,o{|R| }  (3.3)  2  In g e n e r a l the p e r m i t t i v i t i e s causes  the  calculate caused  by  imaginary  component),  in this thesis, the  permittivities.  can  contrast  be  but  I assume that between  complex  (conductivity  f o r the PRC's that I  the PRC i s p r i n c i p a l l y  the r e a l components of the  41 Equation change  (3.2)  is  idealized  thick  layer  sandwiched  between  media  energy i s  reflected  the  PRC  of  permittivity  of  2  permittivities  (PRC = -» dB;  Stratton  if a  e =v/e 1 e  permittivity  to separate the c o n s t i t u e n t  d i e l e c t r i c contrast is  the  at an i n t e r f a c e i s not always sharp. For example,  quarter-wave  Using  because  e,  is  3  and e , no 3  1941,  p. 514).  components of the  (from v e l o c i t y and c o n d u c t i v i t y  contrasts)  d i f f i c u l t . The fading p a t t e r n can be used to determine the  reflector  roughness  (Harrison  The system performance to the smallest 126 dB  and  detectable  the  1972; Neal 1977; M i l l a r  ( r a t i o of the t r a n s m i t - p u l s e s i g n a l ) of the UBC  dynamic  range 80 dB  Hence, I s c a l e the data which c o n t a i n and  the l a r g e s t peaks  geometrical  spreading  remove by using  the  840 MHz  no  signal  the "radar  1983).  -126  dB,  pulse) to -46  dB.  effect  of  to  power  radar i s  (Narod and Clarke  (the c l i p p e d transmit  A f t e r s c a l i n g the data I  1981).  radio  equation"  wave  (Skolnik  1962) :  <P>  = ( G X R )/( 647r r ) 2  2  2  2  (3.4)  2  where <P>  = r a t i o of the r e c e i v e d  G  = one-way antenna  gain  X  = wavelength i n a i r  R  = reflection  r  = range  coefficient  to t r a n s m i t t e d  power  42 If  the  radio  wave  travels  through  i c e , the range must be  c o r r e c t e d f o r the i n c r e a s e d gain from r e f r a c t i o n  at  the  ice  surface:  r' = r +r, /n  where  r'  (3.5)  i s the c o r r e c t e d range, r  a  the range i n a i r ,  r^ the  range i n i c e , and n the index of r e f r a c t i o n of the i c e . I  confirmed  the  126 dB system performance by examining  radar data from Kluane Lake, N.W.T., Canada. The unfrozen lake water  has  a r e l a t i v e p e r m i t t i v i t y of approximately 80;  by equations (3.2) and propagation  loss  (3.3) the lake s u r f a c e PRC  occurs  totally  through a i r .  scale  the  data  during  transit  i s -2 dB.  No  because the path i s  If I remove the g e o m e t r i c a l spreading and  as  explained  above,  I  obtain  performance of 126±2 dB. The data were f i r s t allow  hence  a  system  9 - f o l d stacked to  peaks to be more r e l i a b l y l o c a t e d ; I roughly compensate  f o r the s l i g h t l y using  a  0 dB  increased s u r f a c e PRC  SNR  resulting  from  stacking  by  f o r Kluane Lake i n the performance  calculation. The  PRC  f o r a given r e f l e c t i n g h o r i z o n can be presented  e i t h e r by p l o t t i n g the value above a s e c t i o n or p r o f i l e , or as a  power r e f l e c t i v i t y  s e c t i o n . To produce a power  s e c t i o n I c a l c u l a t e the section  (assuming  PRC  for  every  point  reflectivity in  the  time  some propagation l o s s r a t e ) , then p l o t the  s e c t i o n using d i f f e r e n t grey or colour l e v e l s  (see F i g u r e s  2.7  43 and  2.8) .  3.4.2 DIELECTRIC LOSS AND THE LOSS TANGENT For media with calculate  the  constant  power  dielectric  properties,  l o s s from c o n d u c t i v i t y .  In g e n e r a l , the  r a d i o wave v e l o c i t y i n i c e i s constant below the but  the  conductivity  function  changes  with  depth  of temperature. In t h i s t h e s i s I  conductivity  because  the  I can  firn  because  assume  a  layer, i t is a constant  ice I  examine i s r e l a t i v e l y  plane  wave  thin  (<800 m). An  electromagnetic  z-direction (Stratton  propagating  i n the  through a non-magnetic medium can be d e s c r i b e d  by  1941)  E(z,t)  = E e x p [ i (cjt-kz) ]  (3.6)  0  where E(z,t) E  0  = electric  field  = amplitude  CJ = angular  frequency  t = time k = wavenumber i n z - d i r e c t i o n z =  The  complex  conductivity  distance  relative  permittivity  a and the r e a l part  e'  is  related  to the  of the p e r m i t t i v i t y e by  44 e' = e-ia/cj  (3.7)  The wavenumber i s  k  2  = (cj/c) e'  (3.8a)  2  or by equation (3.7)  k  The  2  = (w/c) (e-io/u)  (3.8b)  2  l o s s tangent tan5 i s d e f i n e d as  tan6  =  (3.9)  a/coe  Thus the wavenumber i s  k  For  = (w/c) e(1-itan5)  (3.10)  k = (w/c)/e(1-itan6)  (3.11)  2  2  small tan6 the wavenumber can be approximated  by  45 k *  (CJ/C)I/T( 1-itan6/2)  (3.12)  T h e r e f o r e , f o r the propagating wave  E ( z , t ) = E e x p [ - z (OJ/C )/7tan5/2 ] 0  • exp[ i w t - i z (co/c )/T]  The  power  integrated  at  depth  over one  z  is  period.  (3.13)  equation The  (3.13)  dielectric  squared, loss  then  rate,  LR  (dB/m), i s r e l a t e d to the r e l a t i v e power which reaches depth z (m) :  LR'Z  = 10«log {exp[z(cj/c)v/7tan5]} dB  For the U B C  (3.14)  lo  radar, co = 2 T T - 8 4 0 - 1 0  6  HZ,  C  =  300 • 1 0  6  m/s,  which  gives  LR = 76.4v/Ttan5  Equation  dB/m  (3.15)  (3.13) i s only v a l i d  f o r constant  e and tan6.  s o l v i n g the wave equation which produces equation depth-varying  permittivity  v a r i a t i o n of the l o s s tangent inversion  theory,  a  function,  one  (3.6)  for  can c a l c u l a t e  By a the  with depth. Using the methods of  calculated  l o s s tangent  function  could  p o s s i b l y be used to estimate the temperature-depth  profile.  4. RADIO ECHO SOUNDING ON NORTHERN ELLESMERE ISLAND  4.1  INTRODUCTION During June 1981,  on  the  northern  more than 2000 l i n e - k i l o m e t r e s of  coast  sounded u s i n g the UBC  of  Ellesmere I s l a n d were r a d i o echo  840 MHz  radar. The  both to r a d i o echo sound the area, and radar on d i v e r s e i c e types. In results  from  the  this  project  was  to t e s t the UBC chapter  I  areas  sounder.  My  They  glacier  calculated  spot  i c e cap.  depths  depth  the  Milne  cap. The v a r i o u s PRC's:  >-l0  dB  g l a c i e r s ; and -30 Milne PRC  and  (<-30  freezing  SPRI  1966,  Mark II  for  the  Ward  and  Hunt  Ice  r e s u l t s agree with t h e i r s , but slightly  have  the b a s a l power r e f l e c t i o n c o e f f i c i e n t  (PRC)  the propagation  and D i s r a e l i G l a c i e r s , and ice for dB  types ice  different.  the  I  for these areas, and determined for  and  present depth p r o f i l e s f o r the Milne  Ward Hunt Ice Shelf r e s u l t s are also  MHz the  were p r e v i o u s l y r a d i o echo sounded i n  D i s r a e l i G l a c i e r s , and Shelf.  840  discuss  by H a t t e r s l e y - S m i t h and others (1969) using the echo  planned  Ward Hunt and Milne Ice Shelves, Milne  D i s r a e l i G l a c i e r s , and Mt. Oxford These  ice  have  shelves;  loss rate  (LR)  the Mt. Oxford i c e  different  measured  -5 to -15 dB  basal  for f l o a t i n g  f o r grounded g l a c i e r s . Some areas of  Ward Hunt Ice Shelves have an abnormally dB); the low PRC  may  i n d i c a t e that b r a c k i s h  the  low b a s a l ice  is  onto the s h e l f bottom, or the i c e i s s a l i n e or b r i n e  soaked i n these areas  (Neal  1977).  47  48 4.1.1  AREAS FLOWN AND  More than the  Ward  1000  Hunt  NAVIGATION  km of r a d i o echo soundings  and  Milne  Ice Shelves, and  were flown the D i s r a e l i  Milne G l a c i e r s  (see F i g u r e 1.2). Four d i f f e r e n t  to  navigation:  provide  photography,  and  transponder  a  Omega,  microwave  system was  dead  over  methods  reckoning,  transponder  and were  aerial  system.  The  to provide accurate n a v i g a t i o n f o r the  Ward Hunt Ice S h e l f ; u n f o r t u n a t e l y the system d i d not  operate.  Oblique a e r i a l photographs were taken from a s i d e window using a 70 mm the  aerial  taking  have  reconnaissance camera.  Cloud  cover  prevented  of high a l t i t u d e v e r t i c a l photographs which would  greatly  aided  the  interpretation  of  the  oblique  photographs. Navigation receiver  and  network of (Hobbs  i s t h e r e f o r e p r o v i d e d by the a i r c r a f t ' s  dead reckoning. The Omega system i s a worldwide  eight  1981,  very-low  frequency  p. 258-271)  which  computer onboard the a i r c r a f t , from  three  or  outputs a i r c r a f t minute  more  geographic  200 m).  it  3 km; fixes  recalibrating improves  the radar data allow me navigator  the  accuracy.  radio at  of  stations  10.2  receives  calculates  Uncorrected  f e a t u r e s which can be observed  The  broadcast  when  stations,  (VLF)  p o s i t i o n to a p r e c i s i o n  (about  approximately  Omega  kHz.  broadcasts  and c o n t i n u o u s l y one-tenth  of  absolute  accuracy  receiver  using  Dead  A  a is  known  reckoning  on the topographic maps and  over in  to r e c a l i b r a t e the Omega c o o r d i n a t e s .  read  the  Omega  r e c e i v e r d i s p l a y at approximately  coordinates  20 s i n t e r v a l s . I  from  the  determined  49 the  radar  t r a c e corresponding  i s recorded  on the  coordinates  for  least on  two  the  voice the  track,  traces  and  flight  commentary  lines  these  interpolated  known p o i n t s . At  each f l i g h t  line;  be  matched  i n t r o d u c i n g approximately than  points  are t h e r e f o r e i n t e r p o l a t e d a c c u r a t e l y ,  ( f o r example d u r i n g turns) are not.  can  smaller  linearly  between  n a v i g a t i o n p o i n t s bracket  points outside  much  to each n a v i g a t i o n p o i n t which  The  voice  to the t r a c e numbers w i t h i n 2 s,  100 m n a v i g a t i o n a l  error.  This  is  the n a v i g a t i o n a l u n c e r t a i n t y of the Omega  system. Errors  in  perturbations ionospheric  in and  Omega  coordinates  the  broadcast  are  caused  pattern  other d i s t u r b a n c e s . Over the  survey  area, these p e r t u r b a t i o n s  which  are  e s s e n t i a l l y constant.  introduce  by  local  arising  from  100  km  x 100  systematic  Hence, i f one  errors  coordinate  be a d j u s t e d to i t s t r u e l o c a t i o n , the other c o o r d i n a t e s can displaced  by  the  same  amount.  using the dead reckoning glacier  data:  features  on topographic  can be  These adjustments were made  f o r example, I ensured that  f l i g h t s followed the v a l l e y c e n t r e l i n e s and  p o i n t s where the a i r c r a f t  km  flew over land maps c o u l d be  and  fixed  islands.  i d e n t i f i e d , the  the the  Where oblique  a e r i a l photographs were used to a i d in these adjustments. With these 1 km. line  c o r r e c t i o n s n a v i g a t i o n a l absolute accuracy R e l a t i v e accuracy i s f a r b e t t e r than  between t r a c e s along this.  a  is typically given  flight  50 4.1.2  ACCURACY OF RESULTS  The a b s o l u t e accuracy of depend  upon  the  scaling  (converting  a l l results  in  this  chapter  accuracy of the r a d i o wave v e l o c i t y and the to  true  power  values)  used,  and  the  accuracy  with which I can l o c a t e the t r a c e . I have p r e v i o u s l y  suggested  that the n a v i g a t i o n a l accuracy  In  some  calculations  depth measurements choice  is  ( f o r example  over t h i n  relatively  is typically  ice),  the  unimportant.  PRC computation  thickness  deep-glacier  by  as  reflections  or  propagation  velocity  For 800 m t h i c k  glaciers,  however, the c h o i c e of a propagation v e l o c i t y can calculated  1 km.  change  the  much as 30 m. For example,  from  9 u.s below  the  ice  surface,  a  propagation v e l o c i t y of 169 m/u.s (Robin and others 1969) g i v e s a depth of 760 m, whereas a v e l o c i t y of 176 m/jus  (Clarke  and  Goodman 1975) g i v e s a depth of 792 m. I use reasons:  a  propagation  this  is  (1975) f o r t h e i r found  the  UHF  velocity  velocity soundings;  of  used the  176 m/jus  for  three  by C l a r k e and Goodman relative  permittivity  f o r the Ward Hunt Ice Shelf was 2.9, although t h i s value  is for s l i g h t l y  l e s s dense i c e (Ragle and others 1964); and  I  have not i n c l u d e d any f i r n - l a y e r c o r r e c t i o n s to compensate f o r the higher v e l o c i t y through  the o v e r l y i n g snow and  firn.  The  f i r n - l a y e r c o r r e c t i o n can i n c r e a s e the depth by s e v e r a l metres (Robin and others 1969) so I p r e f e r to e r r rather  than  underestimating  the  by  velocity.  t h i c k n e s s measurements are accurate to w i t h i n and  resolution errors  overestimating Over  thin i c e ,  the  firn-layer  (±3 m t h i c k n e s s u n c e r t a i n t y ) ; over  thick  51 ice,  thickness  the  error  in  measurements are s u b j e c t to these e r r o r s plus the  radio  wave  velocity  (±10 m  thickness  uncerta i n t y ) . The power l e v e l s are accurate to ±3 dB; from  the  ±2 dB  error  t h i s estimate  i n the l e a s t - s q u a r e s f i t to the Kluane  Lake data, and because the a l g o r i t h m I use to s c a l e  the  data  to t h e i r true power l e v e l s o c c a s i o n a l l y produces a s u r f a c e of -8 dB  i n s t e a d of the  expected  -11  dB  (Robin  1969). Basal PRC's w i l l t h e r e f o r e be accurate to ±3 dB p l u s the propagation  error  introduced  so  by  l o s s r a t e . I use a 0.03  for the i c e s h e l f data. The thick  an  dB/m  However,  propagation  i c e shelves are at the  l o s s r a t e by  a  factor  MT.  the  data  AND  THE MILNE AND  produce  Glacier  PRC,  loss  maximum  of  two  because  of  the  ice thickness; PRC  radar  sections  and propagation  sections  DISRAELI GLACIERS  from f l i g h t s over the Mt. Oxford  i c e cap  (Figure 4.1),  which c l e a r l y  bottom. From these s e c t i o n s I c a l c u l a t e d basal  90 m  l o s s r a t e would cause a  and down the Milne and D i s r a e l i G l a c i e r s to  loss rate  depth.  OXFORD ICE CAP  With  able  chosen  most  a  does not vary with changing  i n c o r r e c t l y chosen propagation  4.2  approximately  i t i s u n l i k e l y that I have i n c o r r e c t l y chosen  i n d i c a t e d b a s a l PRC  change with  PRC  others  even a f a c t o r of two change i n the propagation  the propagation  an  and  incorrectly  r a t e would only change the c a l c u l a t e d PRC's by 5 dB.  is  the  I  show the i c e  ice  thickness,  l o s s r a t e . The D i s r a e l i and  unambiguously  show  the  ice  was  bottom;  Milne the  52 84°00'  Figure  4.1  72°00'  Overland  Flight lines Glaciers.  section but  it  flight over  lines.  t h e Mt.  Oxford  from the Mt. Oxford  i c e cap,  i c e cap  and  down t h e M i l n e a n d  shows  clear  Disraeli  reflections  i s u n c e r t a i n whether the r e f l e c t i o n s are from the i c e  bottom or are d i f f r a c t i o n hyperbolae. If  I assume that  conductivity, results  the propagation l o s s i s caused  I can c a l c u l a t e  (tan6 * 0.0002  to  the l o s s tangent 0.0003)  are  s o l e l y by  f o r the i c e . My  s i m i l a r to the  loss  tangents measured by Ragle and o t h e r s (1964) f o r the Ward Hunt Ice  Shelf.  It  i s i n t e r e s t i n g to note that  the Milne  Glacier  tongue and a t r i b u t a r y g l a c i e r which flows i n t o D i s r a e l i F i o r d  53 have a -5 to -15 and  dB b a s a l PRC  whereas the r e s t  D i s r a e l i G l a c i e r s have a -30  dB basal PRC;  Glacier  this  variation  the  tributary  glacier  are f l o a t i n g . H a t t e r s l e y - S m i t h and others (1969) note i n c r e a s e i n the power r e f l e c t e d  calculated  a  larger  more  from  these  areas.  I  power i n c r e a s e because H a t t e r s l e y - S m i t h  and others used a 35 MHz much  and  Milne  that the  is  tongue  the  suggests  a 10 dB  Milne  of  p u l s e ; I used an 840 MHz  sensitive  to  reflector  pulse  which  roughness because the  wavelength i s more than twenty times s m a l l e r .  4.2.1  ICE THICKNESS  F i g u r e s 4.2, sections  for  4.3,  the  Mt.  and  4.4  Oxford  show  high-pass  filtered  9 - f o l d stacked  them with a 2.0  s e c t i o n s I p l o t t e d depth p r o f i l e s The  processed  radar  i c e cap, D i s r a e l i G l a c i e r ,  Milne G l a c i e r r e s p e c t i v e l y . I f i r s t then  the  us  the  and  data,  window. From these  ( F i g u r e s 4.5,  4.6,  and  4.7).  radar s e c t i o n s are p l o t t e d with the transmit pulse as the  datum; the apparent combination I cannot aircraft  "topography"  of the t r u e topography  separate true altitude  surface  so  f o r the Mt. Oxford (<18  km  Glaciers did I reflection.  The  along  have  ice  surface  and the a i r c r a f t  topography  from  is  the  a  altitude.  changes  in  topography  in a i r c r a f t a l t i t u d e , and p l o t t e d  p r o f i l e s with smooth s u r f a c e  Disraeli  the  I assumed t h a t the observed  r e s u l t s from v a r i a t i o n s  Only  of  the  topography. i c e cap and the upper ends of the flight  difficulty  in  l i n e ) and Milne identifying  the  (<24  km)  bottom  r e f l e c t i o n s from these areas o f t e n appear to  8.00  THG-WRY TRAVEL 6.00 5.00  7.00  i  ... i,„,,,,„  o o  TIME H.00  (uS) 3.00  co o c  • "  o o  CD  TJ O TJ ID Q X I—11-  ID o —I o  m  o I--H  i—•  " j o ID o  :z o  m  I D oo-  Q  o  Z  CD  r —•—i  •  rr—I  z  ^  J=-  o o  2 no  • 'JxM&c?*  ^ ^ ^ ^  -«jr o o  CO •  o o  '-•:-.[,. " f o g ;  '  CO"  o o  CO CD" *  o o  Figure  4.2  Radar  section  from  t h e Mt. O x f o r d  i c e cap.  See F i g u r e 4.1 f o r line location. The data were 9-fold stacked and high-pass filtered. The centres of the black/white pixels are the reflection onsets. The transmit pulse arrives a t 0.3„s; the surface r e f l e c t i o n a r r i v e s a t 1-4„s; a n d t h e b o t t o m r e f l e c t i o n arrives at 4-7„s. The apparent i c e surface topography r e s u l t s from a combination of actual s u r f a c e topography and changes i n a i r c r a f t a l t i t u d e .  0.00  ,.9.00  8.00  THO-WflY TRAVEL TIME 6^ QQ 5.00 14.00  7.00 L___  o  (wSl 3.00  2.00  0.00  o  cn  •  o o  .„» .j^y^,^ ^ ^ ^ ^ ^  ™  t:  MW)>  o o  CO  -  • o o  :D  "TJ  :^ro Q * **» o I-—I  is :D  —i  •_,° ° co —i ID  O .  m o  S  ID  Q CD»  o  "T|  r  O  -  O IT  J=  r~o i—i o m 01  r-,  S j" ^—  o  CO O" •  o o  CO CO" o o  •  o o  CO" o o  Figure  4.3  Radar  section  from  the  Disraeli  Glacier.  See F i g u r e 4.1 for l i n e l o c a t i o n . Note the t r i b u t a r y g l a c i e r which f l o w s i n t o D i s r a e l i F i o r d b e t w e e n 64-76 km. The data were 9-fold stacked and high-pass filtered. The centres of the black/white pixels are the r e f l e c t i o n onsets. The transmit pulse arrives at 0.3 s; the surface reflection arrives at 1-3„s; and t h e b o t t o m r e f l e c t i o n a r r i v e s a t 2-8^s. The a p p a r e n t i c e s u r f a c e t o p o g r a p h y r e s u l t s f r o m a combination of actual s u r f a c e t o p o g r a p h y and c h a n g e s i n a i r c r a f t a l t i t u d e . w  cn cr.  Figure  4.4  Radar  s e c t i o n from  the  Milne  Glacier.  See F i g u r e 4.1 f o r l i n e l o c a t i o n . The M i l n e I c e S h e l f i s b e t w e e n 80-105 km. The data were 9-fold s t a c k e d and h i g h - p a s s f i l t e r e d . The c e n t r e s o f t h e b l a c k / w h i t e p i x e l s a r e t h e r e f l e c t i o n o n s e t s . The t r a n s m i t p u l s e a r r i v e s a t 0.3//S; the s u r f a c e r e f l e c t i o n a r r i v e s a t 1-2^s: and t h e b o t t o m r e f l e c t i o n a r r i v e s a t 2-9 s. The apparent ice surface topography results from a combination o f a c t u a l s u r f a c e t o p o g r a p h y and c h a n g e s i n a i r c r a f t a l t i t u d e . v  cn  CD  57  Figure  4.5  Depth  profile  f o r t h e Mt.  Oxford  i c e cap.  S e e F i g u r e 4.1 f o r p r o f i l e l o c a t i o n . T h e p e a k s of the buried hills are r e l i a b l y i d e n t i f i e d a s b o t t o m ; t h e d o w n g o i n g l i m b s may i n some i n s t a n c e s be d i f f r a c t i o n s . The u p p e r a n d l o w e r l i n e s a r e the ice surface and bottom respectively; the dotted l i n e s d e n o t e a r e a s where t h e r e f l e c t i o n s may be diffractions.  58  a  CD  'o U)  ~o CO l_  CO G  crone  Figure  4.6  Depth  (T09!  profile  0 Kl -  G'OB  r  IOIX) (W) ' T S 3AO0§ 1H9I3H  f o r the D i s r a e l i  OT*-  Glacier.  See F i g u r e 4.1 f o r p r o f i l e l o c a t i o n . N o t e t h e t r i b u t a r y g l a c i e r w h i c h f l o w s i n t o D i s r a e l i F i o r d b e t w e e n 64-76 km. T h e u p p e r a n d l o w e r l i n e s a r e t h e i c e surface and bottom respectively; t h e d o t t e d l i n e s d e n o t e a r e a s where t h e r e f l e c t i o n s may be d i f f r a c t i o n s .  59  OTJSI  Figure  4.7  Depth  rrozi  (  OTJB [OIX) (W)  trrra "TS  p r o f i l e f o r the Milne  OTJE <ro 3AQ8.H 1H3I3H  OOE-  Glacier.  See F i g u r e 4.1 for profile location. The M i l n e I c e S h e l f i s between 8 0 - 1 0 5 km. T h e u p p e r a n d l o w e r lines a r e the i c e surface and bottom respectively; the dotted l i n e s d e n o t e a r e a s where t h e r e f l e c t i o n s may be di f f r a c t ions.  60 consist  of  hyperbolae  downward  opening  are probably  diffraction  patterns.  bottom,  note  that  and  the  their  this.  indicate  downward  Hattersley-Smith  sections  from  indicate strongly undulating subglacial also  the tops of these portions  R e f l e c t i o n - s t r e n g t h a n a l y s i s of these  r e f l e c t i o n s a l s o suggests ( 1 9 6 9 )  hyperbolae;  and  Mt. Oxford topography;  others i c e cap  my  these u n d u l a t i o n s which are apparent  data  on F i g u r e  4.7.  4.2.2 PROPAGATION LOSS RATE AND THE BASAL PRC The measured s t r e n g t h of a r e f l e c t i o n ,  once  system  and  g e o m e t r i c a l spreading l o s s e s have been removed, i s  echo s t r e n g t h = -2«LR«z + PRC  if  z  i s the depth  to the r e f l e c t o r , and the propagation  r a t e LR i s c o n s t a n t . The f a c t o r of equation  (4.1)  two  in  front  of  LR  loss in  (4.1) i s needed because of the two-way propagation of  the r e c e i v e d wave. I depth 4.10).  have  plotted  ice-bottom  reflection  f o r the i c e cap and g l a c i e r data The  system  detection  limit  s t r e n g t h versus  ( F i g u r e s 4.8, 4.9, (the minimum  and  reflection  s t r e n g t h which can be r e s o l v e d assuming some constant  aircraft  t e r r a i n c l e a r a n c e ) i s a l s o shown on these f i g u r e s . R e f l e c t i o n s which l i e c l o s e to t h i s l i n e are b a r e l y above noise  and  the  background  are t h e r e f o r e l e s s r e l i a b l e than r e f l e c t i o n s which  61  ECHO STRENGTH  Figure  4.8  Echo  strength  versus  depth  for  the  (DB)  Mt.  Oxford  ice  cap.  The s y s t e m a n d g e o m e t r i c a l s p r e a d i n g l o s s e s were r e m o v e d f r o m t h e d a t a and 4% o f t h e r e f l e c t i o n s p l o t t e d . The c u r v e d line is the system detection limit assuming a 150 m terrain c l e a r a n c e . R e f l e c t i o n s w h i c h l i e on t h e s t r a i g h t l i n e w o u l d h a v e u n d e r g o n e a 0.032 dB/m propagation l o s s r a t e and a -35.0 dB basal r e f l e c t i o n . The p o i n t s n e a r t h e s y s t e m d e t e c t i o n l i m i t may be d i f f r a c t i o n p a t t e r n s . The p o i n t s appear to curve to the left with increasing depth but may h a v e b e e n t r u n c a t e d by t h e d e t e c t i o n l i m i t . The d i s t a n c e s r e f e r to d i s t a n c e along f l i g h t line.  62  Figure  4.9  Echo  strength  versus  depth  f o r the  Disraeli  Glacier.  The s y s t e m a n d g e o m e t r i c a l s p r e a d i n g l o s s e s were r e m o v e d f r o m t h e d a t a and 2% o f t h e r e f l e c t i o n s p l o t t e d . The c u r v e d line is the system detection limit assuming a 125 m terrain c l e a r a n c e . R e f l e c t i o n s w h i c h l i e on t h e s t r a i g h t l i n e w o u l d h a v e u n d e r g o n e a 0.028 dB/m propagation l o s s r a t e and a -27.2 dB basal reflection. The points f r o m 63-78 km a r e f r o m t h e s m a l l t r i b u t a r y g l a c i e r which flows i n t o the Disraeli Fiord. The points from 0-18 km may be d i f f r a c t i o n s . The d i s t a n c e s r e f e r t o d i s t a n c e a l o n g f l i g h t 1 1 ne.  63  0.0  -JO.O  Figure  4.10  -20.0  Echo s t r e n g t h  -30.0  versus  ECHO STRENGTH -40.0  depth  for  (DB)  -S0.0  the  Milne  -60.0  -10.0  -80.0  Glacier.  The s y s t e m a n d g e o m e t r i c a l s p r e a d i n g l o s s e s were r e m o v e d f r o m t h e d a t a and 2% o f t h e r e f l e c t i o n s p l o t t e d . The c u r v e d line Is the system detection limit assuming a 100 m terrain c l e a r a n c e . R e f l e c t i o n s w h i c h l i e on t h e s t r a i g h t l i n e w o u l d h a v e u n d e r g o n e a 0.022 dB/m propagation l o s s r a t e and a -30.5 dB b a s a l r e f l e c t i o n . The p o i n t s f r o m 78-108 km a r e f r o m t h e M i l n e I c e S h e l f . T h e p o i n t s f r o m 63-78 km a r e f r o m t h e t o n g u e o f t h e Milne Glacier. The points from 0-24 km may be diffractions. The d i s t a n c e s r e f e r to distance along f l i g h t line.  -90.0  64  Table 4.1  Propagation Loss Rate and Basal PRC.  Propagation l o s s r a t e (dB/m)  Loss tangent  Basal PRC (dB)  Ward Hunt Ice Shelf g l a c i e r i c e (-10°C)  0.039  0.0003  Ward Hunt Ice Shelf g l a c i e r i c e (-40°C)  0.013  0.0001  Ward Hunt Ice Shelf sea i c e (-10°C)  1.3  0.01  Mt. Oxford i c e cap ( l e a s t squares)  0.016  0.00012  -42.8  Mt. Oxford i c e cap ( v i s u a l f i t )  0.032  0.00025  -35.0  Disraeli Glacier ( l e a s t squares)  0.028  0.00022  -27.2  Milne G l a c i e r ( l e a s t squares)  0.022  0.00017  -29.5  Propagation l o s s r a t e s (at 840 MHz) f o r the Ward Hunt Ice Shelf have been c a l c u l a t e d using data from Ragle and others (1964, Table I I ) and equation (3.15). The Mt. Oxford i c e cap data were f i t v i s u a l l y because p o i n t s near the system d e t e c t i o n l i m i t are u n r e l i a b l e .  65 lie  well  to  the  left  l e a s t - s q u a r e s f i t to reflections; On the  the  from  the  bottom  reflections  than bottom  figures  may  tongue  of  the  b a s a l PRC  i c e . On  indicate  To I  t h e r e f o r e be  can  -30  loss)  onto the  interference  dB)  from  see  that  and  the  the  clear  diffractions  rather  the  and  PRC  (-45  from the  bottom (Neal the  distribution variation by  of  i n the  -5  the  returned power  1 dB  for PRC  ice  is  glacier  bed  from  results and  the from  reflector (number  power range normalized  maximum occurrence) a g a i n s t r e f l e c t i o n s t r e n g t h spreading,  at  low  power r e f l e c t e d  occurrence  a  dB)  1977).  normalized  within  geometrical  to -15  correcting  objects  reflections  Milne  S h e l f ; the  roughness of the  The  reflections  scattering  the  falling  Milne Ice  small  differentiate  (PRC  before  a  probably  i c e i s b r i n e soaked or b r a c k i s h  shelf  caused  dB  Milne  are  used to  floating  the  and  glacier  there i s a group of  roughness. I p l o t t e d  system,  bottom  glaciers  Glacier,  t h e r e f o r e be  examine q u a l i t a t i v e l y  analyzed  Milne  tributary  Figure 4.10  that the  i c e bottom. The  the  the  can  which flows i n t o D i s r a e l i F i o r d .  and  propagation  freezing  one  echo s t r e n g t h )  the  about 70 m deep with a low  may  clear  show areas of high basal PRC:  tongue  between grounded (PRC  the  the  results.  upper ends of  (low  and  also  glacier  f l o a t i n g ; the  glacier  for  the  reflections.  S h e l f , the  Glacier  (4.1)  echo s t r e n g t h versus depth p l o t s  group s e p a r a t e l y  tributary  l i n e . I have c a l c u l a t e d  summarizes these  i c e cap  Ice  the  equation  Table 4.1  reflections  The  of  propagation,  and  with  of by all  reflection  66  -40.0  T -20.0 0.0 20.0 CENTRED ECHO STRENGTH (DB)  T -40.0  oo*T -40.0  z  Figure  4.11  -20.0 0.0 20.0 CENTRED ECHO STRENGTH (DB)  r -20.0 0.0 20.0 CENTRED ECHO STRENGTH (DB)  Distribution  of basal  reflection  returned  40.0  40.0  40.0  power.  All l o s s e s , i n c l u d i n g t h e PRC a n d p r o p a g a t i o n l o s s e s , a r e r e m o v e d f r o m t h e d a t a b e f o r e t h e d i s t r i b u t i o n o f echoes i s p l o t t e d . The t h r e e h i s t o g r a m s a r e as f o l 1 o w s : a ) Mt. O x f o r d . i c e c a p . D a t a a r e c e n t r e d a r o u n d a line with a 0.032 dB/m propagation l o s s r a t e a n d a -35.0 dB PRC. R e f l e c t i o n s f r o m 12-37 km a r e used. b) D i s r a e l i G l a c i e r . T h e s m a l l p e a k c e n t r e d a t -5 dB i s p r o b a b l y c a u s e d by diffractions. Data are centred around a line with a 0.028 dB/m propagation l o s s r a t e a n d a -27.2 dB PRC. R e f l e c t i o n s f r o m 18-63 km a r e used. c) Milne Glacier. Data are centred around a line with a 0.022 dB/m p r o p a g a t i o n l o s s r a t e a n d a -30.5 dB PRC. R e f l e c t i o n s f r o m 24-63 km a r e used.  68 losses  removed  (Figure  4.11).  The  variation  in  returned  r e f l e c t i o n s t r e n g t h f o r the c l e a r r e f l e c t i o n s i s approximately ±5 dB;  this  large  variation  s u r f a c e i s rough r e l a t i v e to 1977;  Millar  1981).  The  implies the  UBC  that  sounding 840 MHz  the  reflecting  wavelength  radar  has  a  (Neal 21  cm  wavelength i n i c e ; only the smoothest s u r f a c e would not appear rough at t h i s wavelength.  4.3  MILNE ICE SHELF Four  f l i g h t s were flown over the Milne Ice S h e l f (Figure  4.12). Simple p r o c e s s i n g produced is  an  example):  high-pass  9-fold  filtering  clear sections (Figure  stacking  with  a  to  0.5  reduce  us  noise,  window.  I  4.13 then  obtained  e s p e c i a l l y c l e a r bottom r e f l e c t i o n s f o r the areas adjacent the Cape Egerton western  shore  stretching produced reflection  i c e r i s e and a small t r i b u t a r y g l a c i e r on half-way  across only  a  up  the  fiord.  the f i o r d 4 km faint  4 km  wide  from the seaward s h e l f edge  reflection.  have  Figure  4.13  ( o v e r l e a f ) Radar  might  be  labelled  the  adjacent  of  it  I  m u l t i p l e . I c o u l d o b t a i n no r e f l e c t i o n s f o r the area terminus  although  band  aircraft  the  bottom  A  the  the  to  as  to  the Milne G l a c i e r , or f o r the  section  from  the  Milne  northwest  Ice S h e l f .  See F i g u r e 4.12 f o r l o c a t i o n . Two l a r g e b o t t o m c r e v a s s e s , i n d i c a t e d by t h e downward-opening h y p e r b o l a e , b r a c k e t a gap which has no clear bottom reflection. T h i s may imply t h a t the i c e between the c r e v a s s e s i s b r a c k i s h . The s e c t i o n was 9 - f o l d s t a c k e d a n d h i g h - p a s s f i l t e r e d . The c e n t r e s of the b l a c k / w h i t e p i x e l s a r e the r e f l e c t i o n o n s e t s .  0.75_A  1.00H  1.25—  > (0  o  1.50H  1.75  2.00H  2.25—  1  70 corner of the Large  shelf.  bottom crevasses bracket the l o w - r e f l e c t i v i t y band  (see F i g u r e 4.13); perhaps the band i s a huge If the r e f r o z e n i c e was  refrozen  lead.  b r a c k i s h or b r i n e soaked, the returned  power would be decreased  because  the  high-conductivity  ice  would attenuate the p u l s e , and the b a s a l r e f l e c t i v i t y would be low.  4.3.1  Ice The  ICE THICKNESS  F i g u r e 4.14  i s an i c e t h i c k n e s s contour map  Shelf.  n a v i g a t i o n i s accurate to approximately  The  i c e s h e l f averages  off  Cape  Egerton,  about 70 m t h i c k , reaching  and over  where a t r i b u t a r y g l a c i e r western  thick  100 m t h i c k mid-way up the  flows onto the i c e  fiord  shore. I have continued the t h i c k n e s s contours up  onto  i c e r i s e , and  the  small  shelf  tributary  i s continuous with them. No  flown over the g l a c i e r or the i c e r i s e so I have their  northwest  thickness.  The  absence  of  glaciers  f l i g h t s were no  reflections  estimate from  the  corner of the i c e s h e l f and the area adjacent to the  Glacier  terminus  l e s s than the minimum that (10  90 m  km.  the  because the i c e s h e l f  Milne  1  from  the Cape Egerton  of  f o r the Milne  indicates can  be  that the i c e t h i c k n e s s i s resolved  by  the  system  m).  4.3.2  BASAL POWER REFLECTION COEFFICIENT  Equation  (4.1)  i s used to c a l c u l a t e the b a s a l PRC  Milne Ice S h e l f . I estimated the propagation  loss rate  of the to  be  72 0.03  dB/m,  based  upon  the  results  found  in  the  previous  s e c t i o n where the propagation  l o s s r a t e for c o l d e r g l a c i e r i c e  is  upon l o s s tangents found for the  0.02  to  0.03  dB/m,  Ward Hunt Ice Shelf propagation thin  loss  that  even  different The  would  basal PRC It  is  and  (Ragle and rate  a  loss  tangent  interesting  to  flows  the f i o r d  low  several  PRC  spread  percent  4.15.  PRC.  If  meltwater  i s f r e e z i n g onto the s h e l f bottom as could  be  substantially  reduced.  the d i e l e c t r i c c o n t r a s t from f r e s h i c e to layer  l o s s rate g r e a t e r than the 0.03  I used; thus the basal PRC  reducing  would be  dB/m  rate  underestimated.  WARD HUNT ICE SHELF Except  Discovery  for  flight  i c e r i s e and  lines  (Figure  4.16)  over the Cape  the e a s t e r n part of the Ward  S h e l f , the soundings do not  Hunt  show c l e a r bottom r e f l e c t i o n s .  absence of c l e a r bottom r e f l e c t i o n s c o u l d be a r e s u l t of conductivity  within  the  ice  large d i e l e c t r i c attenuation low  which  (see S e c t i o n 3.4.1). As w e l l , the b r a c k i s h i c e would  cause a propagation  4.4  i c e i s so  hundred  s a l t water over the t h i c k n e s s of the b r a c k i s h the  the  note the c o r r e l a t i o n between the basal  b r a c k i s h i c e , the basal PRC would  because the  r e s u l t s are mapped in F i g u r e  of  c h o i c e of  only change the r e s u l t s by s e v e r a l d e c i b e l s .  i c e and  Salt  1964). The  i s not c r i t i c a l  r e l a t i v e l y thin out  others  basal  PRC.  shelf  and  the  (Ragle and others  Ice The high  correspondingly 1964), and  by a  74  Figure  4.16  Flight  line  map f o r  t h e Ward H u n t  Ice  Shelf  The numbers refer to data tapes. The points labelled A and B bracket the radar section presented in Figure 4 . 1 7 .  75 The  soundings from the western part of the Ward Hunt Ice  Shelf show  a  reflection  is  interface 1962; the  faint  reflection  probably  caused  ( f o r example see  at  about  20 m  deep;  this  by the lake ice/basement i c e  Marshall  1955;  Lyons  and  Ragle  Ragle and others 1964). Lyons and Ragle (1962) d e s c r i b e  lake i c e as unconformably o v e r l y i n g the basement i c e i n  broad  syncline.  Leveling  show that the i c e shelf Ragle  1962;  reflection surface  Lyons  others  should a r r i v e  Hunt  F i g u r e 4.17 One can see surface  (Lyons  and  t h e r e f o r e the bottom than  the  i s an example of the best r e s u l t s the  synclinal  reflection,  often  location;  the bottom r e f l e c t i o n  for  most  of  Ice Shelf d e s p i t e many r e p r o c e s s i n g attempts.  seems  layer  just  below  to  be a f a i n t i t does  land  sea  section  from the  bottom.  r e f l e c t i o n at the expected  not  or  the  i s v i s i b l e . The  i s from Cape Discovery i c e r i s e  unfortunately  ice-free  internal  I could achieve.  but no bottom r e f l e c t i o n  undulating r e f l e c t i o n  over  1971);  thick  reflection.  Ward  There  43 m  approximately 0.5 jus l a t e r  I c o u l d not i d e n t i f y the  and seismic surveys, and boreholes  is typically  and  disappear ice  and  while is  flying probably  processing-enhanced n o i s e .  Figure  a  4.17  (overleaf)  Radar  Ward Hunt  Ice  Shelf.  See F i g u r e 4 . 1 6 f o r s e c t i o n location. The surface reflection has been aligned to 1.0»,s. The expected bottom reflection time 1s 1 . 5 „ s ; no r e f l e c t i o n is v i s i b l e at t h i s time. I n s t e a d , a f a i n t r e f l e c t i o n at 1.25,,s 1s v i s i b l e ; t h i s i s p r o b a b l y t h e l a k e 1 c e / s e a 1ce i n t e r f a c e . T h e u n d u l a t i n g r e f l e c t i o n i s f r o m the bottom of t h e Cape D i s c o v e r y ice rise. The faint reflection at 1.7^s i s t h e a i r c r a f t m u l t i p l e r e f l e c t i o n . The b l a c k / w h i t e p i x e l s are the l o c a t e d reflections. The data were 9-fold stacked and high-pass f i l t e r e d .  (sn) em;)  |dABJ»  A B M - O M J  77 4.4.1  ICE THICKNESS  The areas where I c o u l d i d e n t i f y ice  interface  I have  their  flight  part where I o b t a i n e d 45 - 50 On F i g u r e 4 . 1 8 , (the  area  with  appears  to  extend  compared to the map the  included  navigation  results  thickness  three  (about  100  m)  for  the  eastern  m.  the e a s t e r n part of a  d i s c o n t i n u o u s with mainland edge  also  (45 - 50 m  over the Cape D i s c o v e r y i c e r i s e ; however,  they obtained only 30 - 40 m i c e  Shelf  ice/basement  f o r the Cape Discovery i c e r i s e . H a t t e r s l e y - S m i t h  and others (1969) obtained comparable for  lake  (15 - 25 m deep) and the i c e bottom  deep) are mapped i n F i g u r e 4.18. spot-depths  the  clear  the  Ward  bottom  Ice  reflection)  Ellesmere I s l a n d , too  Hunt  and  the  is  shelf  f a r i n t o the A r c t i c Ocean when  of J e f f r i e s  (1982). T h i s may  i n d i c a t e that  i s poor i n t h i s area and the soundings  should  be d i s p l a c e d s e v e r a l k i l o m e t r e s south.  4.4.2 The  DIELECTRIC LOSS AND  BASAL  lake i c e l a y e r which o v e r l i e s  15 - 25 m  l o s s tangent  basement  at -10°C  ice  layer  others 1964); t h i s l o s s tangent rate  the  basement  ice  t h i c k , and the basement-ice l a y e r 20 m t h i c k  and others 1971). The  loss  PRC  of  1.04  dB/m.  A  of  the  and 840 MHz  sea  ice  pulse  (Lyons in  the  i s 0.008 (Ragle  i m p l i e s a one-way  is  and  propagation  r e f l e c t e d from the  shelf  bottom c o u l d s u f f e r the f o l l o w i n g two-way l o s s e s : 1.  2 dB propagation  l o s s from t r a n s i t  i c e having a propagation  through  20 m  l o s s r a t e of 0.05  dB/m.  of  lake  78  Figure  4.18  Ice-layer  thickness  of  the  Ward Hunt  Ice  Shelf.  Included are three spot-depths over the Cape Discovery ice rise. eastern part where a c l e a r b o t t o m e c h o a t 4 5 - 5 0 m d e p t h was o b s e r v e d n e e d t o be d i s p l a c e d t o w a r d s C a p e A l b e r t E d w a r d .  The may  79 2.  40 dB  propagation  loss  basement i c e having 3.  40 dB  reflection  bottom;  from  a propagation  loss  t h i s value  total  loss  approximately -78  only  are  but  indeed  this  the  has  dB.  Thus the expected r e f l e c t i o n  The interface  PRC  the system d e t e c t i o n l i m i t i s  variation is insufficient  PRC  dB/m.  The  strength i s  OF THE  caused  ice  l o s s r a t e . However, I was as -15  dB by assuming a  in  able  presumed part  by  is  Ice  to  propagation  eastern part of the Ward Hunt  LAKE ICE/SEA ICE the  rise  to o b t a i n a good  of approximately -5 to -10  r e f l e c t i o n at is  soaked  limit.  a basal PRC  THE  dB/m.  b r i n e soaked.  to the r e s u l t s from the much t h i c k e r Milne  4.4.3  1.0  of  Ice Shelf i f  82 dB,  basal  l o s s rate of 0.03  20 m  brine  i s observed for the Milne  of the propagation  calculate  Shelf  a  t h i c k n e s s change for the Cape Discovery  100 m;  estimate  from  is  below the d e t e c t i o n The  through  l o s s rate of  reflecting  the areas of low b a s a l PRC The  transit  dB,  Ice  similar  Shelf.  INTERFACE.  lake  ice/basement  ice  the p e r m i t t i v i t y c o n t r a s t  between the lake i c e and  basement i c e . If e,' and  e'  complex  of  basement i c e  permittivities  the  r e s p e c t i v e l y , then by equation reflection coefficient  lake  (3.2)  ice one  and can  2  are  calculate  the  the  R:  (4.2)  80 If  both layers  associated equations  have the  loss (3.7)  same  propagation  tangents  and  are  tan5,  velocity, and  tan5 , 2  R  tan6  [ (1-itan5 /2)-(1-itan8 /2) ] 2  /  1  (4.4)  2  i g n o r i n g terms  of  the  order  tan5  2  R =* i ( t a n 5 , - t a n 5 ) / 4  (4.5)  2  By  equation  contrast  (3.4),  Measuring difficult  often  the  PRC  caused  by  this  loss  tangent  is  PRC = I 0 - l o g  is  by  one can a p p r o x i m a t e R by  [(1-itan6 /2)+(1-itan6,/2)]  By  then  (4.3)  2  small  the  (3.9)  R = (/l-itanSzVl-itanS,)/(/l-itan6 +/l-itan6,)  For  and  ((tan5 -tan5 ) /l6}  the  1  PRC of  because  obscures  (4.6)  2  1 0  the  the  2  the  lake  energy  interface  ice/basement  backscattered reflection.  ice  interface  from t h e  From  surface  identifiable  81 r e f l e c t i o n s I f i n d that the PRC near and  Ward  I s l a n d , to -20  the Cape Discovery  the PRC  Hunt  Cape  Discovery  increase  to be 0.04.  Ragle and  others  is  than  Marshall marks  then decreases to -40  of  the  dB  island near  i c e r i s e . I do not yet know whether  this  dB PRC  0.01;  i n c r e a s e the PRC function  dB mid-way between the  backscattered  the l o s s tangent  contrast  i s l a r g e r than any  (1964). T h e i r l a r g e s t c o n t r a s t  lake  -40  dB  This contrast  (1955) and  the  about  by  roughness.  To produce a -40  less  ice r i s e ,  from  i s r e a l or r e s u l t s from energy  increasing surface  need  increases  a  0.01  Crary  would  reported  (at  840  MHz)  dB  PRC.  c o n t r a s t produces a -52  (1958) note that a heavy dust  ice/basement  ice  i n t e r f a c e . The  by  dust  layer could  because the e f f e c t i v e p e r m i t t i v i t y would be a dust  and  i c e p e r m i t t i v i t i e s , and  (Smith and  PRC  r e s u l t s from a combination of v e l o c i t y c o n t r a s t ,  l o s s tangent c o n t r a s t , and ice/basement i c e i n t e r f a c e .  the dust  Glen and  Paren 1975).  dust  concentration probably  Evans 1972;  the  concentration  at the  The  lake  5. CONCLUDING REMARKS  5.1  DATA PROCESSING AND My  in  b a s i c p r o c e s s i n g scheme c o n s i s t s of reducing the noise  a radar s e c t i o n , then p l o t t i n g the s e c t i o n . High-frequency  noise by  RADIO ECHO SOUNDING  (higher than the s i g n a l s one low-pass  low-frequency reflector  filtering noise  across  caused  roughness and  i s looking for) i s  by  the  backscattered  i c e i n c l u s i o n s i s reduced  f i l t e r i n g down the s e c t i o n .  Nonlinear  AGC  enhance low-amplitude r e f l e c t i o n s . AGC and  processed  Amdahl 470 V/8) all with  the an  produce  the  can  filtered  processing.  attached  energy by  from  high-pass  be  used  Versatec  to  data.  data on a l a r g e mainframe computer  but minicomputers should be  basic  (stacking);  must be used c a u t i o u s l y  should only be a p p l i e d to c a r e f u l l y I  section  reduced  able  to  (an  perform  I used a PDP-1l/34a minicomputer V-80  electrostatic  plotter  to  the g r e y - s c a l e s e c t i o n s , and an I n t e r n a t i o n a l Imaging  Systems ( I S Model 70) 2  image processor  to produce  the  colour  r e f l e c t i v i t y section. The involve  problems digitizing  which the  other  researchers  analogue  tremendous q u a n t i t y of d i g i t a l d a t a .  The  then data  set  for  512-point  t r a c e s . Each p o i n t i s 14 b i t s : the e n t i r e  tape  encounter  storing  analyzed  is  this  tapes,  might  which  the I  t h e s i s c o n t a i n s the e q u i v a l e n t of 300,000 data  set  more than 300 megabytes. N i n e - t r a c k , h i g h - d e n s i t y computer i s the only p r a c t i c a l  storage medium.  82  83 The  processing  I report i n t h i s t h e s i s reduces noise on a  t r a c e - t o - t r a c e b a s i s . Noise r e d u c t i o n techniques on  the  e n t i r e radar  s e c t i o n ( s p a t i a l and temporal  c o u l d be developed. The p l o t t e d (reflection plotted);  arrival  which  time  sections  rather  i n f u t u r e work I plan  than  to  are  filtering)  time  sections  reflector  convert  operate  depth  these  to  is  depth  sections.  5.2 RADIO ECHO SOUNDING ON NORTHERN ELLESMERE ISLAND I Shelf  obtained  good i c e t h i c k n e s s r e s u l t s f o r the Milne Ice  (70 - 100 m), the Milne and D i s r a e l i G l a c i e r s (they  thin  from >700 m to 0 m), and f o r the eastern part of the Ward Hunt Ice Shelf for  (45 - 50 m). I c o u l d not obtain t o t a l  the r e s t of the Ward Hunt Ice S h e l f , but I d i d o b t a i n the  depth to an reflector  internal  reflector  i s probably  Where I obtained the  i c e thickness  basal  the  (15 - 25 m).  This  lake ice/basement i c e i n t e r f a c e .  good i c e t h i c k n e s s r e s u l t s , I c o u l d c a l c u l a t e  PRC:  almost  0 dB  f o r i c e shelves;  grounded g l a c i e r s ; -20 to -40 dB f o r the Ward Hunt internal and  interface;  -5 to -15 dB  propagation  loss  approximately The  Hattersley-Smith shelf  but  overflown  -15 dB  for  their  -30 dB f o r Ice  f o r the Cape Discovery  floating  glaciers.  The  Shelf  ice rise; measured  r a t e f o r the Milne and D i s r a e l i G l a c i e r s i s  0.03 dB/m (tanS  Milne  internal  Ice and others equipment  0.00025).  Shelf  is  surprisingly  thick.  (1969) attempted to sound t h i s i c e d i d not  operate  u n t i l they had  the s h e l f and were onto the Milne G l a c i e r .  I  could  84 f i n d no r e f e r e n c e literature similar Milne  and  to the Milne consequently  Ice  Shelf  expected  the  to that of the Ward Hunt Ice Shelf  thickest  are  places.  adjacent  The  (>~10  dB)  thickness  (about  the  A l b e r t Edward i c e ice  a l a r g e basal PRC  rise.  could  The  be  would  flow  low  the  basally-accreted brackish fiords  visualized  topography; the rather  than  to a  i s large  by  over  i c e contours.  flows  "hills"  c o u l d be g r e a t l y reduced  (thick  with soaking  flowing  from  over the  The  flow  the bottom as an  through  (Neal  brine  i c e s h e l v e s , but  considering  water  of  Meltwater  beneath the  to the Cape  associated  "valleys"  can  the or the sea be  inverted  (thin  ice)  i c e ) . If the meltwater i s  f r e e z i n g onto the s h e l f bottom as b r a c k i s h  It  is  under t h i c k i c e for the  PRC  result  ice.  water, f o l l o w i n g the t h i n n e s t easily  ice  basal PRC  The  i s more  i c e r i s e , and  part of the Ward Hunt Ice S h e l f , adjacent  thinner  to be  40 m).  where  f i o r d . The  the  under the t h i c k i c e .  I a l s o obtained eastern  regions  to the Cape Egerton  t r i b u t a r y g l a c i e r mid-way up the  i c e , the b a s a l  PRC  1977).  i s i n t e r e s t i n g to note that  Keys  and  others  (1968)  that the Ward Hunt Ice Shelf dams meltwater in D i s r a e l i  F i o r d to a 43-44 m depth; t h i s suggests t h a t the 44 m t h i c k . I obtained only  in  Ice Shelf averages approximately 70 m t h i c k and  than 90 m t h i c k in  found  thickness  f o r the e a s t e r n  suggests  that  ice shelf  is  c l e a r bottom r e f l e c t i o n s from the s h e l f  part where i c e i s t h i c k e r than 45 m.  meltwater  flows  western part of the s h e l f , and  out  This  from the f i o r d under  the  that where the water flows,  the  basal PRC i s  reduced.  REFERENCES C l a r k e , G.K.C. and Goodman, R.H. 1975. Radio echo soundings and ice-temperature measurements i n a surge-type g l a c i e r . J o u r n a l of Glac i o l o g y , V o l . 14, No. 70, p. 71-78. Crary, A.P. 1958. A r c t i c i c e i s l a n d and i c e s h e l f s t u d i e s , Part I . A r c t i c , V o l . 11, No. 1, p. 3-42. Crary, A.P. 1960. A r c t i c i c e i s l a n d s and i c e s h e l f s t u d i e s , Part I I . A r c t i c , V o l . 13, No. 1, p. 32-50. Evans, S. and Smith, B.M.E. 1969. Radio equipment for depth sounding i n polar i c e sheets. Journal of S c i e n t i f i c Instruments ( J o u r n a l of Physics E ) , S e r i e s 2, V o l . 2, p. 131-136. Glen, J.W. and Paren, J.G. 1975. The e l e c t r i c a l p r o p e r t i e s of snow and i c e . J o u r n a l of G l a c i o l o g y , V o l . 15, No. 73, p. 15-38. H a r r i s o n , C.H. 1970. R e c o n s t r u c t i o n of s u b g l a c i a l r e l i e f from radio echo sounding r e c o r d s . Geophysics, V o l . 35, No. 6, p. 1099-1115. Harrison, C.H. 1972. Radio propagation e f f e c t s i n g l a c i e r s . Unpublished Ph.D. t h e s i s , Cambridge, U.K., 193 p. Hattersley-Smith, G. 1963. The Ward Hunt Ice S h e l f : recent changes of the i c e f r o n t . J o u r n a l of G l a c i o l o g y , V o l . 4, No. 34, p. 415-424. H a t t e r s l e y - S m i t h , G., and o t h e r s . 1969. G l a c i e r depths i n northern Ellesmere I s l a n d : a i r b o r n e r a d i o echo sounding i n 1966, by G. H a t t e r s l e y - S m i t h , A. Fuzesy, and S. Evans. DREO T e c h n i c a l Note 69-6, Geophysics Hazen 36. 46 p. Hobbs, R.R. 1981. Marine N a v i g a t i o n 2: Celestial and E l e c t r o n i c , second e d i t i o n . U n i t e d States Naval I n s t i t u t e , Maryland. 343 p.  86  87 Jeffries, M. 1982. The Ward Hunt Ice S h e l f , s p r i n g A r c t i c , V o l . 35, No. 4, p. 542-544.  1982.  Kanasewich, E.R. 1975. Time Sequence A n a l y s i s i n Geophysics, second e d i t i o n . The U n i v e r s i t y of A l b e r t a Press, Edmonton, Canada. 364 p. Keys, J . , and others• 1968. On the oceanography of Disraeli Fjord on northern Ellesmere Island, by J . Keys, O.M. Johannessen, and A. Long. Manuscript Report, No. 6, Marine Science Centre, M c G i l l U n i v e r s i t y , M o n t r e a l , Canada. 7 p. + f i g u r e s . Lyons, J.B. and Ragle, R.H. 1962. Thermal h i s t o r y and growth of the Ward Hunt Ice Shelf. Union Geodesique et Geophysique Internationale. Association Internationale d'Hydrologie S c i e n t i f i q u e . Commission des Neiges et des Glaces. Collogue d'Obergurgl 10-9-18-9 1962, p. 88-97. Lyons, J.B., and o t h e r s . 1971. Basement i c e , Ward Hunt Shelf, Ellesmere Island, Canada, by J.B. Lyons, Savin, and A.J. Tamburi. J o u r n a l of G l a c i o l o g y , Vol. No. 58, p. 93-100.  Ice S.M. 10,  Lyons, J.B. and o t h e r s . 1972. Growth and grounding of Ellesmere I s l a n d i c e r i s e s , by J.B. Lyons, R.H. Ragle A.J. Tamburi. J o u r n a l of Glac i o l o g y , V o l . 11, No. p. 43-52.  the and 61,  M a r s h a l l , E.W. 1955. S t r u c t u r a l and s t r a t i g r a p h i c s t u d i e s the northern Ellesmere i c e s h e l f . A r c t i c , V o l . 8, No. p. 109-114.  of 2,  Millar, D.H.M. 1981. Unpublished Ph.D.  Radio-echo l a y e r i n g in p o l a r i c e t h e s i s , Cambridge, U.K. 177 p.  sheets.  Narod, B.B. 1979. UHF r a d i o echo sounding of Yukon glac i e r s . Unpublished Ph.D. t h e s i s , U n i v e r s i t y of B r i t i s h Columbia, Vancouver, Canada. 183 p. Narod, B.B and C l a r k e , G.K.C. 1983. UHF radar system for airborne surveys of i c e t h i c k n e s s . Canadian Journal of E a r t h Sciences, V o l . 20, No. 7, p. 1073-1086.  88 Neal, CS. 1976. Radio-echo power p r o f i l i n g . G l a c i o l o g y , V o l . 17, No. 77, p. 527-530.  Journal  Neal, C S . 1977. Radio echo s t u d i e s of the Ross Ice Unpublished Ph.D. t h e s i s , Cambridge, U.K. 87 p. Prager, B.T. 1982a. Radar data Unpublished internal report, Columbia, Vancouver, Canada.  processing University  of  Shelf.  programs. of B r i t i s h  Prager, B.T. 1982b. PROCESS2: a data p r o c e s s i n g and p l o t t i n g package• Unpublished internal report, University of B r i t i s h Columbia, Vancouver, Canada. Racal T e c h n i c a l Handbook. 1978. Racal Store 4D/7D Technical Handbook, fourth e d i t i o n . Racal-Thermionic L t d . , Hythe, Southampton, England. 32 p. + c i r c u i t diagrams. Ragle, R.H., and o t h e r s . 1964. Ice core s t u d i e s of the Ward Hunt Ice S h e l f , 1960, by R.H. Ragle, R.G. B l a i r , and L.E. Persson. J o u r n a l of G l a c i o l o g y , V o l . 5, No. 37, p. 39-59. Robin, G. de Q. and o t h e r s . 1969. I n t e r p r e t a t i o n of r a d i o echo sounding i n p o l a r i c e sheets, by G. de Q. Robin, S. Evans, and J.T. B a i l e y . P h i l o s o p h i c a l T r a n s a c t i o n s of the Royal Society of London, S e r i e s A. V o l . 265, No. 1166, p. 437-505. S k o l n i k , M.I. 1962. I n t r o d u c t i o n to Radar Systems. McGraw-Hill Kogakusha, L t d . , London. 648 p. Smith, B.M.E., and Evans, S. 1972. Radio-echo sounding; absorption and s c a t t e r i n g by water i n c l u s i o n and i c e lenses. Journal of Glac i o l o g y , V o l . 11, No. 61, p. 133-146. S t r a t t o n , J.A. 1941. Electromagnetic Company, New York. 615 p.  Theory. McGraw-Hill  Book  Watts, R.D. and Wright, D.L. 1981. System f o r measuring thickness of temperate and p o l a r i c e from the ground or from the a i r . J o u r n a l of Glac i o l o g y , V o l . 27, No. 97., p. 459-469.  

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