A Survey of Radar Rain Measurement Techniques

Abstract

Several methods used to estimate rainfall rate R are surveyed. The distribution N(D) of drop sizes is of central importance in determining the reflectivity factor Z, attenuation rate K, and R. With single-parameter measurement techniques either of the remotely sensed parameters Z or K can he used to estimate R when gross assumptions on N(D) can be made. If N(D) can be described by a two-parameter distribution, dual measurement techniques can better estimate R without invoking these coarse assumptions. A review is made of three techniques whereby two variables might be measured. 1) dual wavelength in which Z and K are remotely measured, 2) dual polarization in which reflectivity is measured with two orthogonal polarizations, and 3) raingage-radar combinations whereby in situ point measurements of R and radar measurement of Z or R are combined to obtain a better assessment of rain over areas between gages.