Recent Improvements in Arctic and Antarctic Marine Gravity: Unique Contributions from CryoSat-2, Jason-1, Envisat, Geosat, and ERS-1/2

Abstract:

Marine gravity from satellite altimetry has become a primary tool for investigating the tectonics of the remote ocean basins as well as unexplored continental margins especially in the polar regions where shipboard data are sometimes sparse. Gravity field accuracy depends on three factors: spatial track density, altimeter range precision, and diverse track orientation. Recently two new non-repeat altimeter data sets have become available from CryoSat-2 and Jason-1 to augment the data provided by Envisat, Geosat, and ERS-1/2. One question that arises is what is the unique contribution of each altimeter? To answer that question we have constructed 5 global gravity models omitting data from CryoSat-2, Jason-1, Envisat, Geosat, and ERS-1/2 respectively. We find each satellite provides an important contribution. CryoSat-2 has the best polar coverage and highest track density so provides the greatest improvement overall. Envisat has excellent high latitude coverage where it provides the greatest improvement in the Arctic. Jason-1 has the lowest orbital inclination so provides a dramatic improvement in the E-W gravity component for latitudes < 60. We have verified an overall gravity accuracy in the Gulf of Mexico of 1.6 mGal. This is sufficient to reveal previously unknown sub-seafloor structure buried under sediment on the continental margins. The accuracy in the Arctic is generally worse and highly variable depending on the extent of permanent ice cover. The major error sources in marine gravity are now due to ice coverage, inaccurate coastal tide models, mesoscale variability, permanent dynamic topography, and the errors in land gravity, which migrate into the nearby oceans during the conversion from geoid height to gravity. The high-resolution gravity field (~80 km) being provided by the GOCE mission may help to reduce these error sources.