An apparent wave height dependence in the sea‐state bias in Geosat altimeter range measurements

Abstract

The sea‐state bias in Geosat altimeter range measurements expressed as a percentage of significant wave height (SWH) is examined as a function of SWH. The bias is shown to be approximately a fixed −3.5% of SWH for SWH smaller than about 4 m. For larger SWH, the bias decreases in magnitude approximately linearly to a value of about −1.5% of SWH for 6 m SWH. Because of this “saturation effect” associated with large SWH, estimates of the Geosat sea‐state bias which have been based on the assumption of a fixed percentage of SWH are too small by up to 1.5% of SWH. The saturation effect is so large at high latitudes in the southern hemisphere (where about 1/4 of the SWH values exceed 4 m) that it apparently overwhelms any wind speed dependence in the sea‐state bias suggested by several recent studies. The apparent SWH dependence found in this study appears to be the result of attitude and sea‐state errors in the Geosat altimeter on‐board tracking algorithm.