Until recently, gravity maps of the world’s oceans and continental margins relied on the data generated from two Geodetic Mission satellites: Geosat and ERS-1, which flew in the 1980s and 1990s.
These satellites used radar altimeters to measure the height of the sea surface, from which free-air gravity was calculated. Since 2004, Getech has been in the forefront of research into finding new methods of improving the accuracy and resolution of the final gravity field. This has involved developing new innovative methods of ‘picking’ the first return of the altimeter wave pulse and integrating the sea-surface height along-track profile data into the best combined geoid grid before converting to gravity anomalies (Fairhead et al., 2001).
This approach relies on the application of micro-levelling technology, which has the advantage that it can cope readily with a range of track directions; moreover, the gridded data sets can be fully visualized at all times and gross or minor errors, or inconsistencies can be readily identified and fixed.
Our original 2004 solution over all the continental margins of the world showed that we could resolve wavelengths in the gravity field down to less than 15 km.
In 2008, we generated a version of satellite gravity we termed the Trident solution by stacking three independently derived solutions of free-air gravity from the Geosat and ERS-1 satellites: our 2004 solution, the DNSC08 solution from the Danish National Space Centre (2008) and Sandwell & Smith v16.1 (2004).
Today there are a further three satellites that have either completed or are planned to complete Geodetic Missions: Cryosat-2, Jason-1 and HY-2A. Since these satellites also have a range of orbital inclinations, the effective orbital spacing at the Equator will reduce from ~3-4 km to under 2 km. This improved coverage, combined with continual developments in processing methodologies and techniques, is currently being incorporated into our new Multi-Satellite Altimeter Gravity Study (2103-2016). The preliminary results from this study show, amongst other things, that we can improve the reliability of the signal closer to the shore line than was previously possible.