Coherence spectra for a) satellite -vs- ship gravity and b) gravity -vs- topography.

Abstract.

The July 1995 declassification of the entire Geosat GM satellite altimeter data set enabled a joint Scripps/NOAA effort to compute a new (version 7.2) marine gravity field on a 2-minute grid. This gravity field covers the world's oceans between 72 N and 72 S, and is derived from a combination of ERS-1 and Geosat GM and ERM data. An earlier NOAA Geosat-only gravity field solution was confined to the southern latitudes because the 1992 declassification was limited to GM data south of 30 S. A simple coherence analysis between accurately-navigated ship gravity profiles and comparable gravity profiles obtained from the gravity grids reveals that the Scripps/NOAA gravity field is coherent with ship gravity down to ~>= 23-30 km. This slight increase in resolution over the previous NOAA Geosat-only gravity field (short-wavelength resolution of ~26-30 km) implies that the increased spatial coverage provided by the ERS-1 altimeter, when combined with Geosat, improves the solution. Coherence anlayses between satellite gravity and ship topography, and ship gravity and ship topography, show that even shorter wavelength gravity anomalies (~13 km) are present in sea-surface measurements made by ship. Even so, the Scripps/NOAA marine gravity field does an excellent job of resolving most of the short-wavelength gravity anomalies covering the world's oceans.

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