Accuracy Of Gravity Anomalies Research Articles

Performance of Jason-2/GM altimeter in deriving marine gravity with the waveform derivative retracking method: a case study in the South China Sea

Deriving marine gravity is one of the important applications of satellite altimetry in earth science. The quality of marine gravity derived from each altimeter data always is limited by the range measurement on the certain ground track spacing. We assess the performance of Jason-2/geodetic-mission (GM) altimeter in deriving marine gravity by the improved range from waveform retracking. The singular value decomposition was applied to denoise waveforms, and the waveform derivative retracking was employed to improve the sea surface heights (SSHs). Finally, Jason-2/GM-derived gravity anomalies on 1′ × 1′ grids were determined by the least-squares collocation method based on the resample 5 Hz SSHs around the South China Sea (SCS). Assessed by ship-borne data from different institutions, the accuracy of Jason-2/GM-derived gravity is consistent with that of the V27.1 and DTU13 models. Moreover, with the application of waveform derivative retracking, the accuracy of gravity anomalies has improved from 6.6 mGal before retracking to 5.5 mGal after retracking over the open ocean, and from 8.9 to 7.4 mGal over the coastal area. It is better than the results obtained by traditional retracking methods, including off-center of gravity (OCOG), 5-β, threshold, Ice-1, and maximum likelihood estimator-4 (MLE4). Furthermore, evaluated by V27.1 and DTU13, the result shows root mean square (RMS) difference of 2.0 mGal and 3.0 mGal, respectively. Therefore, the waveform derivative retracking is an effective method for altimeter data, and the accuracy of derived gravity is an improvement by retracked SSHs.