Backscatter and Attenuation by Falling Snow and Rain at 96, 140, and 225 GHz

Abstract

The results of measurements of backscatter cross section per unit volume and attenuation for falling snow and rain at 96, 140, and 225 GHz are presented. The attenuation due to rain is almost independent of the measurement frequency, but for snow the attenuation is considerably greater at 225 GHz than at 96 GHz. The rain attenuation generally varies with the rain accumulation rate in accordance with an aRb relationship for a Laws and Parsons drop-size distribution. The attenuation at all three frequencies is about 3 dB/km for a rain rate of 4 mm/h. The attenuation due to snow varies linearly with airborne snow-mass concentration, with the average rates of increase being 0.9, 2.5, and 8.7 (dB/km)/(g/m3) at 96, 140, and 225 GHz, respectively. Generally the attenuation for snow is lower than that for rain. The backscatter cross section per unit volume for rain at 96 GHz is about -35 dB m 2 /m 3 for a rain rate of 4 mm/h. The backscatter from snow at 96 GHz is much lower than that for rain under equivalent accumulation rates or airborne mass concentrations. Snow backscatter at 140 and 225 GHz is comparable but higher than that at 96 GHz. © 1988 IEEE