C-Band Dual-Polarization Radar Observables in Rain

Abstract

C-band dual-linear polarization radar observables are simulated from disdrometer measurements in rainfall and from gamma-model raindrop-size distributions. It is shown that rainfall is clustered in certain sections of planes formed by selected pairs of radar observables, such as (ZH, ZDR), (ZH, ZDP), (ZH, KDP), and (?, ZDR). Measurements lying outside these rainfall cluster regions can be interpreted as being from ice- and mixed-phase hydrometeors. Relationships for estimating rainfall rate R from radar measurements of ZH, KDP, and (ZH, ZDR) are derived, and the latter is shown to produce the best results. An important problem for C-band measurements in the presence of rainfall is attenuation. For this purpose, relationships are derived for estimating specific attenuation and specific differential attenuation from the specific differential phase. The backscattering differential phase shift, which is a potential source of error in estimating KDP, is shown to be very sensitive to the drop-size distribution. The effects of raindrop temperature and canting on the derived relationships are discussed. Finally, S-band relations similar to those obtained at C band are also presented.