Analysis of the fetch-related bias in altimeter wind speed measurements

The present interpretation of the radar cross section sigma exp 0 measured by satellite altimeters implies that the rms wave slope gamma is controlled solely by the local wind. However, parameters of wave spectra, including the exponent in the power law for the equilibrium range, depend on sea maturity. The latter is characterized by the nondimensional fetch, x = gX/U-squared. Consequently, gamma and sigma exp 0 are controlled by both U and the wind fetch X. Geosat data for one year are used jointly with in-situ wind and wave observations to assess the fetch-related error trend in altimeter wind speeds. This trend results in overestimated winds in the regions and seasons characterized by a high x, and vice versa. A procedure for wind speed retrieval based on processing sigma exp 0 jointly with the significant wave height information contained in the altimeter wave forms is proposed.