A unique data set consisting of expendable bathythermograph (XBT) observations from repeated Gulf Stream crossings was used to provide ground-truth for GEOS-3 altimeter measurements of temporal sea height variability. The XBT data were obtained by NAVOCEANO using ocean liners travelling between New York and Bermuda as observation platforms. Approximately 120 crossings, each consisting of 50-60 XBTs, were made between October 1969 and November 1974. Dynamic heights were calculated using XBT profiles and temperature/salinity relationships from historical data. Results were then compared to sea height variability measured from the differences in altimeter profiles between pairs of collinear GEOS-3 passes. The comparison shows that the satellite measurements are in good agreement with the conventional shipboard observations. Additionally, it is shown that dynamic height variability correlates very highly with temperature variability at depths between 100 and 450 meters. This relationship indicates that in the Gulf Stream region, the sea surface topography in conjunction with historical data could be used to infer subsurface thermal structure.
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