Marine Gravity Field Mapping from Altimetry – Advancement with 2nd Generation Altimeters

Until the launch of Cryosat in 2010 the only geodetic data available for deriving high resolution marine gravity fields were the 1985 Geosat GM and 1995 ERS-1 phases E and F. Geodesists therefore spent the better of 15 years improving these GEOSAT and ERS-1 data. With the launch of the second generation altimeters CryoSat and SARAL/AltiKa and the completed geodetic
missions from Jason-1 as part of the retirement orbit, a new era in satellite altimetry has been initiated. Since 2010 the amount of geodetic mission altimetry has nearly four-doubled. At the same time the signal-tonoise ratio in these new satellite’s range measurements is better than that of Geosat and ERS-1, and this is leading to huge improved resolution of marine gravity anomalies. Today the quality of altimetric marine gravity is on the order of 1.5 to 2 mGal depending on region. This surpasses what can be obtained from marine gravity in many regions of the world. The quality of global high resolution marine gravity field will always be limited by the random noise level in the radar range measurement as well as the ground track
spacing. Over the years geodesists have made significant advances in retracking algorithms, cutting range error nearly in half, and leading to improvements that have been a benefit to oceanography. Cryosat-2 provides for the first time altimetry throughout the Arctic Ocean up to 88°N as well as delay- Doppler (SAR) altimeter in scattered regions aroumd the world where the multi-looked on-board processing can be used for improved range precision at even higher Altimetric Contributions to Gravity Field, Marine Geodesy, Bathymetry Modeling
along track resolution than conventional satellite altimetry (LRM). In the near future we are looking towards several new revolution in high resolution marine gravity field mapping. The first will be the completion of the 2-year Jason-2 End of Life geodetic mission which will decrese the groundtrack spacing from 8 km today to 4 km which will enable scientist to resolve further high resolution in the marine gravity field. The second will be the availability of ultrahigh resolution SWOT altimetry from year 2021.