Extreme wind conditions observed by satellite synthetic aperture radar in the North West Pacific

Abstract

In this paper some recent results on SAR observation of extreme surface wind conditions are summarized. Particular emphasis is put on the investigation of typhoons occurring in the North West Pacific. The study is based on the use of ENVISAT ASAR wide swath images (400km x 400km), which allow synoptic measurements of the complete mesoscale system at high resolution (150m). Surface wind speed for typhoon cases is determined from SAR measurements using the geophysical model function CMOD5. Further structures observed in the image like streaks indicating wind direction and the ring of maximum wind speed are additionally taken into account to reconstruct the typhoon wind field. The influence of heavy rain on the radar cross section is estimated from an existing radiative transfer model and compared to the SAR measurements. A new technique for the estimation of typhoon intensity from SAR data is presented, which makes use of a parametric type model. The main goal of the paper is the improvement of the estimation of maximum typhoon intensity using SAR data.