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UBC Theses and Dissertations

Measurement of copolar attenuation through the bright band at 4 & 7 GHz Van der Star, Jack A.


This thesis describes an experiment designed to measure microwave propagation through the bright band at 4 and 7 GHz. The path is located approximately 100 kilometers east of Vancouver, British Columbia, Canada, forming part of the Trans Canada Telephone System microwave network. The path is coastal and mountainous in nature, 41.3 kilometers in length and experiences an average annual rainfall of 1600 mm/year. Due to these factors and an elevation differential of 1227 m between transmitting and receiving sites, the 0°C isotherm and hence bright band effect normally exist along the path from November to April. A measurement system based on remote telemetry is used to obtain high resolution and accurately time-correlated data. Received signal levels are taken from five selected 4 and 7 GHz microwave channels which are sampled at a rate of 10 Hz. Meteorological information is obtained from five locations along the path and sampled at a rate of 1 Hz. The data thus collected are then time-correlated as it arrives at the University of British Columbia (Vancouver) recording site where it is analyzed using high-level language routines developed as part of a propagation data base management system. A detailed description of both the measurement system and the data management system are provided in the thesis. Results from several precipitation systems indicate that bright band attenuation can be many times (in dB per kilometer) greater than attenuation due to equivalent amounts of rain. This is described by an Excess Attenuation Ratio (EAR) defined as the ratio of the excess attenuation in dB/km calculated using the Laws and Parson distribution at 0°C. The experimental results compare favourably with those predicted by the theoretical model of Matsumoto and Nishitsuji. A scintillation type fading phenomenon superimposed on the broad-band fade has also been observed during bright band propagation conditions. From the preliminary results this phenomenon appears to be correlated with sudden changes in differential temperature between transmitter and receiver sites and thus a corresponding change in the thickness of the bright band.

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