Theoretical investigations of the sea state bias dependence on sea state

Following continuing technological improvements, errors in mean sea level (MSL) estimates from satellite altimeter measurements have steadily decreased and are now of the order of only a few centimetres. Hence, the sea state bias (ssb) now represents the largest contributor to the MSL error with typical values of a few percent of the significant wave height. Yet, the dependence of the sea state bias on sea conditions is poorly understood as current ssb corrections rely on empirical relationships with wind and significant wave height derived statistically from satellite or airborne measurements. In this paper, a theoretical approach is adopted for a more rigorous examination of the ssb dependence on sea conditions. Existing ssb theories by Srokosz (1986) and Elfouhaily et al. (2000) are implemented and applied to directional spectra from buoys or generated by the WAM third-generation wave model. The theoretical ssb coefficient is computed for a wide range of wind/wave/current conditions to examine its dependence on sea state and various metocean parameters. Issues relating to the relative importance of the high and low frequency parts of the spectrum are discussed and a parameterisation of the ssb coefficient in terms of the ocean mean square slope is proposed