Satellite mapping of the Antarctic gravity field

The production and analysis of the Antarctic digital magnetic anomaly map will be greatly aided by complementary gravity data. They help to constrain thickness variations of the crust and related magnetic effects that may be used for correcting long-wavelength errors in near-surface magnetic survey compilations. They also limit ambiguities in geological interpretations of magnetic anomalies. Antarctic free-air gravity anomalies are available from the 1° Earth Gravity Model 1996 (EGM96). These coefficients satisfy gravity estimates from satellite radar altimetry, as well as surface or near-surface measurements in roughly 75% of the 30 arc-minute blocks south of 60°S. For the remaining blocks, the EGM96 predictions are limited in resolution to degree 70 based on satellite orbital analyses. Anomaly predictions over the unsurveyed regions of the Antarctic will be greatly improved by additional orbital measurements from the pending low-altitude (i.e., 150-500 km) CHAMP and GRACE satellite missions of ESA and NASA, respectively. Shorter wavelength anomalies are available from Geosat and ERS-1 & 2 radar altimetry data for marine regions away from the shoreline that compare very well with modern, good-quality shipborne data. Over the Gunnerus Ridge region, for example, satellite altimetry-derived free-air gravity predictions at a 3-5 km grid interval have an accuracy of about 3 mgals or less.