Influence of sea surface backscattering on the spaceborne radar measurements of rainfall

A critical issue for TRMM Precipitation Radar (PR) is to estimate path integrated attenuation using Surface Reference Technique (SRT), which assumes uniform ocean surface backscattering background at precipitation scale, and attributes the difference in measured surface backscattering cross sections inside and outside of storms to path-integrated attenuation. Since ocean surface winds are the major force that controls the strength of the backscattering signals, it is very desirable to examine or “explain” the measured ocean backscattering using ocean surface wind fields. To this end, the authors examined the feasibility of retrieving ocean surface winds from TRMM PR data for the benefit of the surface reference technique. A geophysical model function, a forward model, is developed based on ocean surface wind speed retrieved from TRMM Microwave Imager data. A field-wise wind retrieval procedure, an inverse model, is formulated using maximum likelihood estimation. TRMM PR data are analyzed to demonstrate that the PR derived ocean wind speed can explain the ocean backscattering successfully. Possible improvements on the existing surface reference technique are also discussed