Detection of Boundary Layer Water Clouds by Spaceborne Cloud Radar

Abstract

A model for the radar reflectivity of boundary layer water clouds is constructed using cloud droplet spectra fitted to a truncated gamma distribution. The spectra were derived from several recent field experiments. Realistic space-based radar returns are simulated that take into account the pulse shape, digitization interval, averaging volume, and variations in droplet concentration, cloud depth, and cloud-top height. The results show that the long pulse length of the proposed radar is responsible for smearing out the real reflectivity spatially so that the space-based detected clouds occupy a volume far exceeding that of the ?observed? cloud. However, the effect of smearing is reduced by the limited receiver sensitivity. Cloud volume of boundary layer clouds is overestimated by between 30% and 100% using proposed radar parameters. Even if clouds are detected, the radar reflectivity convoluted by the pulse shape is sufficiently different from the originally observed reflectivity to seriously impede the retrieval of accurate cloud liquid water content.