New insights into the radar backscattering from the water surface at different radar frequencies and polarizations in the presence of rain and wind

In order to interpret different radar contrasts on images of rain events over the ocean acquired by a multi-frequency/multi-polarization synthetic aperture radar (SAR), laboratory and field measurements have been performed. The aim of this investigation is to develop a method for estimating rain rates of small scale rain events over the ocean using radar backscatter data. The radar backscatter measurements of the water surface during the field experiments have been carried out using a four-frequency/multi-polarization scatterometer, during the laboratory measurements using a 9.8 GHz (X band) scatterometer at the wind wave tank of the University of Hamburg under different wind and rain conditions. The authors compare the results of these measurements with the radar cross-sections derived from SAR-images of rain cells over the ocean by calculating the ratios of the radar cross-sections at co- and cross-polarization (CCP-ratios). With help of further calculations performed using a composite surface model, and some basic assumptions the authors interpret radar images of rain cells more quantitatively by giving first estimates of rain rates