Modeling Polarimetric Response of Spaceborne Synthetic Aperture Radar Due to Precipitating Clouds From X- to Ka-Band

Spaceborne synthetic aperture radars (SARs) exhibit the appealing imaging feature of very high spatial resolution (on the order of meters). At frequency above C-band, the atmospheric effects, and particularly the signature of precipitating clouds, cannot be neglected on both amplitude and phase received signal. The impact of precipitation on SAR slant-view imagery is due to a combination of surface and volumetric backscattering, coupled with path attenuation and with a significant dependence on frequency, polarization, and spatial distribution of hydrometeors. The actual spatial resolution (on the order of hundreds of meters) of these effects is larger than the SAR nominal one due to the random nature of the moving distributed atmospheric target. This paper is devoted to the numerical forward modeling of SAR response at X-, Ku-, and Ka-bands due to precipitating clouds in order to better understand the physical correlation between SAR echo and precipitation. To this aim, a high-resolution mesoscale atmospheric numerical model is used to extract the 3-D distribution of liquid and ice hydrometeors. A detailed sensitivity analysis of SAR backscattering is carried out with respect to hydrometeor columnar and slant water contents, relative contribution of volumetric and surface scattering, incidence angle and ground inhomogeneity, polarimetric observables, and frequency scaling signatures. The numerical results show that the slant-view of SAR observations plays a determinant role and the use of a multifrequency polarimetric SAR may be very useful to characterize precipitation effects and, to a certain extent, retrieve its content at very high spatial resolution.