Radar Snowfall Measurement

Abstract

Measuring snowfall by radars faces many extra challenges compared to radar rainfall measurements due to the facts that snow particles have low density and are non-spherical in shape. The low density makes their scattering intensity weak, therefore only detectable by highly sensitive radars. The non-sphericity of the snow particle, on the other hand, makes the conversion from radar reflectivity to snowfall rate extremely uncertain. Because of these difficulties, global snowfall maps were not available until the availability of CloudSat Cloud Profiling Radar (CPR) measurements, which operates at 94 GHz and has a minimum detectability better than −26 dBZ. In this article, using CPR measurements as an example, we first describe the theory and methods of measuring snowfall by space-borne radars, followed by new findings that have resulted from CloudSat observations and ideas on how to use CloudSat to guide passive microwave sensors for snowfall retrievals.