Ocean Wave Measurements in High and Complex Sea State by SAR Wave Mode Data and Numerical Wave Model

Abstract

The Synthetic Aperture Radar (SAR) onboard the European Satellite ERS-2 is operated in wave mode over the global oceans, whenever no image mode data acquisition is requested. In the scope of the Wave Atlas Project, ESA provided a two-year wave mode dataset of ERS-2 SAR raw data mainly collected during 1999 and 2000, which was reprocessed to single-look-complex (SLC) imagettes at DLR using the BSAR processor. The processed dataset contains daily between 1300 and 1500 images of 5 km (azimuth direction) by 10 km (range direction) size acquired over the global ocean. In the present paper new algorithms to derive sea state developed at the German Aerospace Center (DLR) are briefly introduced and used to determine SAR derived individual and spectral sea state parameters. As an example, a severe North Pacific storm, which produced significant wave height (SWH) above 10 m along the northern great circle shipping route, is presented. The sea state generated is analyzed in detail using the comparison of SWH derived from ERS SAR, Altimeter and the ocean wave model WAM. The results are intercompared and validated. Further an example of a cross sea is analyzed. A cross sea case occurred in the South East Pacific and was captured clearly by consecutive ERS-2 SAR wave mode images acquired on August 10, 2000 at 17:31 UTC. The WAM model spectra, SAR cross spectra and nonlinear SAR retrieved (PARSA) spectra together with derived integral parameters of the spectra as retrieved from SAR images are used to analyze the generation and development of the cross sea.