Attenuation and space diversity statistics calculated from radar reflectivity data of rain

During the summer of 1973 the rain reflectivity environment in three-dimensional space was routinely recorded on digital tape at Wallops Island, Va. A mode of operation consisted of sampling periodically azimuth intervals over regions in which the rain activities were most intense and widespread. A series of plan-position indicator (PPI) sweeps over these intervals were implemented at a sequence of elevation angles starting from up io an angle above which the reflectivity values were below a designated threshold level. Approximately 500 such raster scans were acquired in which each scan was obtained in less than 4 min and covered a range interval of 10 to 140 km. Using the above data base, reflectivity profiles along representative earth-satellite paths were determined from which attenuation and space diversity statistics were calculated at the frequencies of 13 and 18 GHz. Specifically, the form was used to deduce the total path attenuation, where is the attenuation coefficient (dB/km), and is the reflectivity factor (mm⁶/m³). The constants and were calculated using the raindrop distribution for thunderstorm activity as proposed by Joss. Probabilities that the attenuations exceed given fade depths, diversity gain as a function of fade depths, and diversity gain as a function of site separation distances are characterized and compared at the various frequencies. For the space diversity mode, a site spacing of 15 km is shown to give rise to a near optimum condition for the diversity gain. Furthermore, the diversity gain has been demonstrated to be minimally influenced by the transmitter frequency.