Hurricane Precipitation Observed by SAR

Abstract

The SAR-observed backscatter from the ocean's surface is related to the surface wave spectrum, which is in turn related to the near-surface vector wind. This enables retrieval of near-surface winds from SAR images. Rain impacting the surface affects the wind-driven surface wave spectrum and roughens the surface. Rain can be observed in SAR images due to the effects the rain has on the surface and scattering and attenuation of the radar signal by the falling rain. With its high resolution SAR is a useful sensor for studying rain. This Chapter focuses on SAR observation of rain in ocean images. The effect of rain on the SAR backscatter image is modeled. Using a case study of RADARSAT ScanSAR SWA images of Hurricane Katrina, rain effects are analyzed for three different incidence angle ranges using collocated ground-based Doppler weather radar (NEXRAD) rain measurements. The rain-induced backscatter observed by the ScanSAR is consistent with C-band scatterometer-derived wind/rain scattering models when the polarization difference between the sensors are considered. New insights into the temporal behavior of rain effects on the small-scale surface wave spectrum derived from the ScanSAR images are presented.