THE SEA-STATE BIAS IN ALTIMETER ESTIMATES OF SEA-LEVEL FROM COLLINEARANALYSIS OF TOPEX DATA

The wind speed and significant wave height (H-1/3) dependencies of the sea state bias in altimeter estimates of sea level, expressed in the form Delta h(SSB) = bH(1/3), 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 H-1/3. A parameterization of b as a quadratic function of wind speed only, as i n the formulation used to produce the TOPEX geophysical data records ( GDRs), is significantly better than a parameterization purely in terms of H-1/3. However, a four-parameter combined wind speed and wave heig ht formulation for b (quadratic in wind speed plus linear in H-1/3) si gnificantly improves the accuracy of the sea state bias correction. Th e GDR formulation in terms of wind speed only should therefore be expa nded to account for a wave height dependence of b. An attempt to quant ify the accuracy of the sea state bias correction Delta h(SSB) conclud es that the uncertainty is a disconcertingly large 1% of H-1/3.