Impact of incoherent backscattering upon radar echoes above 10 GHz

Radar observations of precipitation profiles from space are simulated in order to evaluate the impact of precipitation incoherent backscattering upon radar returns above 10 GHz at nadir. Spaceborne and airborne radar frequencies at 13.8, 24, and 35 GHz are chosen for carrying out simulations at nadir. Realistic precipitation profiles are extracted from a microphysical mesoscale cloud model simulation and averaged with respect to classes of surface rainrate. The classical radar equation is reformulated taking into account the multiple scattering phenomenon through a general definition of the apparent reflectivity. Numerical results show that opposite effects are due to the combination of path attenuation and multiple scattering. When first-order scattering approximation holds, path attenuation is the predominant contribution and tends to reduce the equivalent reflectivity, while multiple scattering tends to increase it, especially in the cloud regions characterized by large albedo. For intense rainfall cases the rainrate profiles can be significantly overestimated when derived from apparent radar reflectivity simply corrected by two-way single-scattering path attenuation.