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

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.