The accuracy of altimétric surfaces

Summary. Estimates of the shape of the sea surface as determined from satellite altiméters have become of increasing importance in geophysics, geodesy and physical oceanography. The most effective error reduction procedures used in producing these surfaces have been some version of a crossing-arc analysis. The problem with this procedure is the absence of an easy means of evaluating the noise structure of the final result. By recasting the problem as one of objective mapping (optimal estimation) we both optimize the error reduction and obtain an explicit estimate of the wave-number structure of the final altimétric surface. Examples, suitable to a small computer, have been generated to show that the error reduction along the sub-satellite tracks is very great, with most of the residual lying in long wavelengths.