Marine gravity anomaly from Geosat and ERS 1 satellite altimetry

TLDR

Satellite altimeter profiles from Geosat and ERS‑1 can be converted into grids of vertical gravity gradient and gravity anomaly. By taking along‑track derivatives to suppress radial orbit error, interpolating ascending and descending slopes onto uniform grids, and combining these into vertical deflection grids from which vertical gravity gradients and Fourier‑derived gravity anomalies are computed, the authors generate high‑resolution gravity maps from dense Geosat and ERS‑1 data. The resulting satellite‑derived gravity anomaly achieves 4–7 mGal accuracy on random ship tracks and 3 mGal on repeat‑track lines, providing the first detailed view of ocean‑floor structures and enabling applications such as inertial navigation, seafloor depth prediction, and petroleum exploration.

Abstract

Closely spaced satellite altimeter profiles collected during the Geosat Geodetic Mission (∼6 km) and the ERS 1 Geodetic Phase (8 km) are easily converted to grids of vertical gravity gradient and gravity anomaly. The long‐wavelength radial orbit error is suppressed below the noise level of the altimeter by taking the along‐track derivative of each profile. Ascending and descending slope profiles are then interpolated onto separate uniform grids. These four grids are combined to form comparable grids of east and north vertical deflection using an iteration scheme that interpolates data gaps with minimum curvature. The vertical gravity gradient is calculated directly from the derivatives of the vertical deflection grids, while Fourier analysis is required to construct gravity anomalies from the two vertical deflection grids. These techniques are applied to a combination of high‐density data from the dense mapping phases of Geosat and ERS 1 along with lower‐density but higher‐accuracy profiles from their repeat orbit phases. A comparison with shipboard gravity data shows the accuracy of the satellite‐derived gravity anomaly is about 4–7 mGal for random ship tracks. The accuracy improves to 3 mGal when the ship track follows a Geosat Exact Repeat Mission track line. These data provide the first view of the ocean floor structures in many remote areas of the Earth. Some applications include inertial navigation, prediction of seafloor depth, planning shipboard surveys, plate tectonics, isostasy of volcanoes and spreading ridges, and petroleum exploration.