Validation of Significant Wave Height From Improved Satellite Altimetry in the German Bight

Abstract

Significant wave height (SWH) is mapped globally through satellite altimetry. SWH estimation is possible because the shape of a pulse-limited altimetric waveform depends on the sea state. The algorithm for SWH also depends on the width of the point target response (PTR) function. Particularly challenging for SWH detection are coastal data, due to land and calm water interference in the altimeter footprint, and low sea states, due to an extremely sharp leading edge in the waveform that is consequently poorly sampled. Here, Adaptive Leading Edge Subwaveform Retracker (ALES), a new algorithm for reprocessing altimetric waveforms, will be validated for SWH estimation in the German Bight. This challenging region presents both low sea state and coastal issues, and an extended network of buoys of the Bundesamt fuer Seeschiffahrt und Hydrographie is available for the in situ validation. Reprocessed data from Envisat, Jason-1, and Jason-2 missions are validated against the three offshore buoys. The in situ validation is applied both at the point nearest to the buoy and at all other points along track. The skill metrics is based on bias, standard deviation, slope of regression line, and number of cycles with correlation larger than 90%. We also tested the impact of the inclusion of two additional waveform samples that are provided in the Envisat Sensor Geophysical Data Records and the adoption of different values for the width of the PTR. Results show that near coast ALES estimations of SWH are generally better correlated with buoy data than standard processed products.