Evaluation of Geosat altimeter data with application to tropical Pacific sea level variability

Abstract

Repeated Geosat altimeter measurements of sea level at ground track intersections (crossovers) and along collinear nests of profiles were used to evaluate Geosat data by (1) construction of a regional, precise surface made up of intersecting sea level profiles, (2) determination of the magnitude of the electromagnetic (EM) bias, and (3) generation of sea level time series and anomaly maps. The first procedure, after elimination of radial ephemeris error and other long‐wavelength signals, established the data's internal precision at a few centimeters. With regard to the EM bias, comparing repeated sea level profiles for different values of significant wave height (SWH) gave a value of about 1% of SWH. The final process yielded a record of sea level whose accuracy was tested by comparison with in situ measurements and wind‐driven model results. On the basis of these analyses we conclude that Geosat data can determine sea level changes with an rms accuracy of approximately 4 cm for time scales of a month or longer. For determining sea level variability, Geosat geophysical data records are a high‐quality, long‐term data set of significant value for the study of ocean dynamics.