Radar-Derived Statistics on Slant-Path Attenuation at 10 GHz


  • R. R. Rogers


Attenuation due to rain at 10 GHz over the radar line of sight has been measured automatically during the past three summer seasons. Data from five months were analyzed to give statistics on the frequency of occurrence, the extent in azimuth, the duration, and the dependence on elevation angle of 5- and 10-db attenuation events. Results show that the frequency of occurrence diminishes rapidly as the elevation increases from horizontal to 10°, and is essentially constant from there on to 20°. 5 db is exceeded 10 hours per year at 3° elevation, 4 hours per year at 10°, and 3.5 hours per year at 20°. At all elevations 10 db is exceeded about one-fifth as frequently as 5 db.

The azimuth extents of attenuating rain regions vary from 1°, the narrowest extent measurable, to values exceeding 60°. At low elevations the distributions of azimuth extent are strongly peaked at the narrow end. With increasing elevation the distributions flatten. The average azimuth extent of a 5-db region increases approximately linearly from 10° at an elevation of 3° to 33° at an elevation of 20°. For all elevations the average 10-db extents are about half the 5-db extents. The average duration of a 5-db event decreases from about 30 min at near-horizontal paths to less than 10 min at an elevation of 20°. For all elevations the average duration of a 10-db event is about two-thirds that of the 5-db event. These results indicate the characteristics of rain attenuation to be expected over satellite-to-ground communication links for the Montreal area.