Modeling of rain cell impact on Ku Band scatterometer data

The presence of rain within a scatterometer cell can significantly modify the backscatter coefficient and hence alter the wind vector retrieval. Rain perturbations result from volume scattering and attenuation by rain drops in the atmosphere and changes of sea surface roughness by impinging rain drops. For scatterometers operating in the Ku-band, attenuation and volume scattering are strong (10 times larger than at C-band). A theoretical model, based on radiative transfer formulation, including rain attenuation and change is first presented. The change in surface roughness, a complex phenomenon, is not fully understood and is not considered. As a scatterometer cell covers several hundreds of km², inhomogeneities of rain within the cell will further modify the measured backscatter, particularly in case of small intense precipitating rain cell. Using analytical rain cells models, such as the ones estimated from rain radar data, the effects of partial beam filling by rain is investigated