Satellite-based radar measurements for validation of high-resolution sea state forecast models in German Bight

Kurzfassung

The estimation of marine and meteorological parameters is an important task for operational oceanographic services. Remote sensing Synthetic Aperture Radar (SAR) data from TerraSAR-X/Tandem-X satellites have been used for validation and verification of new developed coastal forecast models. In comparison to in-situ buoy measurements at a single location allows remote sensing to cover large areas and to estimate the spatial distribution of investigated characteristics. Methods to derive wind speed and sea state using simple empirical models from high-resolution SAR data have been developed by DLR especially for coastal applications: a new nonlinear wind algorithm XMOD-2 and new empirical model function XWAVE-2 for obtaining significant wave height from X-band data. Both algorithms are capable of taking into account finescale effects in coastal areas. In order to improve forecast accuracy in coastal area a new high-resolution Coastal Wave Model (CWAM) for the German Bight and the western Baltic Sea has been developed by the German Meteorological Service (DWD) and the German Maritime and Hydrographic Agency (BSH) with resolution of ~900m and more accurate mapping of coastlines (1) and coupled to a irculation model (2). Uncertainties are present when dealing in coastal areas: wind input implying well-timed atmospheric front propagation and physical interaction-processes in shallow water caused by interplay between waves, currents and bottom become important. Due to currents and bottom influence the waves refract, dump, become steeper and break. The lost wave energy dissipates and transfers into turbulence and acceleration of flow currents (radiation stress). Sea state estimated from series of TerraSAR-X images cover strips with length of ~200km and width of 30km over German Bight from East-Frisian Islands to Danish coast. The acquired data with more than 50 images were used for model validations. The comparisons show a number of local variations due to variety in bathymetry and wind fronts.