Annual validation of significant wave heights of ERS‐1 synthetic aperture radar wave mode spectra using TOPEX/Poseidon and ERS‐1 altimeter data

Abstract

Significant wave heights retrieved globally during 1994 from low bit rate imagette spectra of the synthetic aperture radar (SAR) operating in the intermittent wave mode (SWM) onboard the first European Remote Sensing (ERS‐1) satellite (Hsswm) are validated using independent, buoy‐validated satellite altimeter data from TOPEX/Poseidon (Hstop) and ERS‐1 (Hsers). Hsswm is retrieved using the extended inversion algorithm of the fully nonlinear wave‐to‐SAR spectral integral transform [Hasselmann et al., 1996]. The statistical comparison shows that globally retrieved Hsswm agree remarkably well with collocated data of both altimeters. Histograms of global Hsswm are well approximated by the universal lognormal distribution function. A small but systematic underestimation of Hsswm with respect to both altimeters by 0.1 m is noticed. This bias is small compared to the uncorrelated root‐mean‐square (rms) deviation of 0.5 m. The underestimation originates from underestimations of the high sea states dominated by wind sea. The entire range of swell waves of Hsswm, however, corresponds very closely to Hstop. Thus the high accuracy of SWM‐retrieved swell wave heights substantiates their suitability for model validation and for operational wave data assimilation. To achieve also reliable estimates of the high sea states, the combined analysis of wave and wind data from both modeling and observation is the most promising approach.