The sea state bias in altimeter estimates of sea level from collinear analysis of TOPEX data

The wind speed and significant wave height (H1/3) dependencies of the sea state bias in altimeter estimates of sea level, expressed in the form AhssB -- bHi/3, are examined from least squares analysis of 21 cycles of collinear TOPEX data. The bias coefficient b is found to increase in magnitude with increasing wind speed up to about 12 m s -1 and decrease monotonically in magnitude with increasing Hi/3. A parameterization of b as a quadratic function of wind speed only, as in the formulation used to produce the TOPEX geophysical data records (GDRs), is significantly better than a parameterization purely in terms of Hi/3. However, a four-parameter combined wind speed and wave height formulation for b (quadratic in wind speed plus linear in Hi/3) significantly improves the accuracy of the sea state bias correction. The GDR formulation in terms of wind speed only should therefore be expanded to account for a wave height dependence of b. An attempt to quantify the accuracy of the sea state bias correction AhssB concludes that the uncertainty is a disconcertingly large 1% of Hi/3.