Radar Attenuation and Reflectivity Measurements of Snow With Dual Ka-Band Radar: Fid-Bau Portal

Radar Attenuation and Reflectivity Measurements of Snow With Dual Ka-Band Radar

Nakagawa, Katsuhiro

There is insufficient understanding of backscattering and attenuation for the radiowave remote sensing of snow because ground measurements of snow in the Ka-band are limited. This study estimates the equivalent radar reflectivity factor (Z_e) and specific attenuation (k) of snow using a dual Ka-band radar (KaR) system comprising two identical Ka-band instruments. To evaluate the estimations, estimated k{-}Z_e plots of rain events are compared with plots estimated from the raindrop size distribution. The two k{-}Z_e plots have similar power-law relations. In contrast, k{-}Z_e plots of snow have complex tendencies. Among snow events, the tendencies of k{-}Z_e relations depend on surface temperature. When surface temperature exceeds 0 °C during snow events, k{-}Z_e data are scattered and there are k values higher than those of rain. In contrast, when surface temperature is below 0 °C during snow events, both k and Z_e are low and the k{-}Z_e plots show no relation. In the former (latter) cases, wet (dry) snow is probably dominant. The differences in k{-}Z_e relations of snow are attributed to the differences in backscattering and attenuation characteristics between wet and dry snow. To confirm the existence of wet/dry snow, snow particle data obtained using a two-dimensional video disdrometer on the ground are analyzed. Velocity-size distributions are clearly different in wet- and dry-snow cases. For dry-snow cases, snow particles of dry snow and graupel occasionally coexisted.