Reprocessed coastal altimetry data improve the quality of Significant Wave Height estimation
17 October 2014
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.
Data from Envisat, Jason-1 and Jason-2 have been reprocessed with ALES, a new algorithm for reprocessing altimetric waveforms in coastal and open ocean already successfully employed for sea level retrieval. The SWH retrievals have been validated against three off-shore buoys of the Bundesamt fuer Seeschiffahrt und Hydrographie (BSH) located in the German Bight, a region that presents both low sea state and coastal issues.
A widespread underestimation of low SWH is found in the latest version of Envisat SGDR product and the cause is the value used to approximate the width of the PTR function in the Brown functional form for the SGDR retracking. Our analysis suggests that the previous value of =0.53 rt (with rt being the time resolution) is a better one.