A Surface Wind Model–Based Method to Estimate Rain-Induced Radar Path Attenuation over Ocean

Abstract

The rainfall retrieved using the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) depends on estimating the radar signal path-integrated attenuation using the surface reference technique (SRT). This technique 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 surface wind is the major environmental variable that controls the strength of the ocean backscattering, it is very desirable to examine the impact of surface wind variation on the retrieved attenuation. To this end, we 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 (TMI) data. A fieldwise wind-retrieval procedure, an inverse model, is formulated using maximum likelihood estimation. Comparison of the conventional SRT with the path-integrated radar attenuation derived using the wind field approach shows an rms difference of 1?2 dB, which is consistent with previous study based on data collected from the Jet Propulsion Laboratory Airborne Rain-Mapping Radar (ARMAR). In addition, there is excellent agreement between wind fields retrieved from TRMM PR and TMI data.