Global analysis of ocean wave systems from SAR wave mode data

Abstract

One of the major goals of the European Remote Sensing Satellites ERS-1 and ERS-2 were applications in ocean wave research and wave forecasting. For the first time, two-dimensional spectral information on the sea state globally, continuously, and in quasi real time are provided in the so-called SAR wave mode. To use not only the spectral but also the image information of these data, a global set of single look complex (SLC) synthetic aperture radar (SAR) images (imagettes) was processed from ERS-2 wave mode raw data, using the BSAR processor developed at DLR. SAR imagettes are used to analyze recently developed algorithms for wind and wave measurements. As the new European Satellite ENVISAT will provide cross spectra on a global and continuous basis, interest in the described techniques is growing. Two-dimensional ocean wave spectra are derived from SAR imagettes by quasi-linear inversion of the SAR imaging mechanism. Individual wave systems are detected by a so-called partitioning algorithm. The resulting wave parameters are analyzed and compared to model data. To take into account the complete nonlinear SAR imaging mechanisms, wave model spectra are simulated forward into cross spectra and compared to observations. Using this approach cases of significant inconsistencies between SAR and model data can be detected. With our 3 week data base in 1996 (about 30,000 imagettes) statistics are calculated. Finally, we derive daily maps showing areas with significant deviations between simulated and observed cross spectra.