Estimation of the Sea-State Bias in Radar Altimeter Geosat Data from Examination of Frontal Systems

Abstract

The sea-state bias is the deviation of the sea surface height as seen by a satellite altimeter due to differential scattering by the crest and troughs of waves and to oversimplification of the radar waveform algorithms that calculate this height. Here the sea-state bias is estimated by automatically analyzing with a least-squares technique the along-track deviation of sea surface in the case of fronts of significant wave height (SWH). Twenty-two thousand profiles of 1500-km length of Geosat altimeter data are analyzed. Since a very strict selection was applied, only nine clear front situations are found. Among these five correspond to atmospheric frontal situations as suggested by the altimetric wind profiles. The sea-state bias is of 3.6% ±0.6% of SWH (2σ error). The four other fronts are interpreted as swell fronts: they present smaller biases of the order of 1.0%±1.6% of SWH. These results are in agreement with experimental studies and justify the calculation of sea-state bias as a function of sea maturity.