Sea level time series in the equatorial Pacific from satellite altimetry

Abstract

Geosat, a Navy satellite launched in March 1985, will provide the first long‐term, global altimeter data set. These observations will enable construction of monthly sea level maps of the equatorial Pacific, much like those presently derived from island tide gauges, but with greatly improved spatial resolution and coverage. During the first half of the Geosat mission, the satellite ground track will not repeat, requiring time series analyses to be based on altimetric height differences at crossover points. We have used the 3‐month Seasat data set in the equatorial Pacific to test the feasibility and accuracy of this procedure. Crossover differences were sorted into diamond‐shaped areas with zonal and meridional dimensions of 200 and 400 km, respectively. The sea level time series in each of these areas was then determined using objective analysis. These computations show agreement within 5 cm between altimeter and island tide gauge observations on time scales greater than 1 month. Using this technique, we propose to construct monthly maps of sea level variability in the equatorial Pacific for the duration of the Geosat mission (approximately 3 years).