Algorithm for sea surface wind retrieval from TerraSAR-X and TanDEM-X data

Kurzfassung

A Geophysical Model Function (GMF), denoted XMOD2, is developed to retrieve sea surface wind field from Xband TerraSAR-X/TanDEM-X (TS-X/TD-X) data. In contrast to the previously developed XMOD1, XMOD2 consists of a nonlinear GMF, and thus, it depicts the difference between upwind and downwind of the sea surface backscatter in X-band SAR imagery. By exploiting 371 collocations with in situ buoy measurements which are used as the tuning dataset together with analysis wind model results, the retrieved TS-X/TD-X sea surface wind speed using XMOD2 shows a close agreement with buoy measurements with a bias of -0.32 m/s, an RMSE of 1.44 m/s and a scatter index (SI) of 16.0%. Further validation using an independent dataset of 52 cases shows a bias of -0.17 m/s, an RMSE of 1.48 m/s, and SI of 17.0% comparing with buoy measurements. To apply XMOD2 to TS-X/TD-X data acquired at HH polarisation, we validate three X-band SAR Polarisation Ratio (PR) models that were tuned using TS-X dual polarisation data by comparing the retrieved sea surface wind speed with buoy measurements.