Retracking Jason-1 GM and Cryosat-2 LRM Waveforms for Regional High-Resolution Marine Gravity Modelling
Deng, Xiaoli1; Andersen, B. Ole2; Stewart, G. Mark1; Idris, H. Nurul1
1The University of Newcastle, AUSTRALIA; 2Technical University of Denmark, DENMARK
For the first time since 1995 two satellite altimetry missions, Jason-1 geodetic mission (GM) and Cryosat-2 Low Resolution Mode (LRM), are globally measuring sea surface heights at very high spatial scales of ~8 km from Jason-1GM and Cryosat-2 LRM (406-day and 369-day repeat orbits, respectively). During the last decade, in addition, the realisation of the satellite gravity missions of CHAMP, GRACE and GOCE, the acquisition of new gravity data and the development of novel processing methodologies have led to the determination of global geopotential models with better accuracy and higher resolution. The previous EGM96 with spatial scale of ~110 km has been improved by the EGM2008 up to a much higher spatial level of ~16 km at full wavelength. The advance in the representation of higher frequencies by the geopotential models and current altimeter measurements suggest a new opportunity to determine the high-resolution regional gravity models over oceans. Sea surface heights extracted from coastal altimetry waveform retracking techniques have recently shown significant improvement in terms of the precision and along-track resolution. This study, thus, retracks currently available altimeter waveforms from Jason-1 GM and Cryosat-2 LRM and derives accurate sea surface heights for modelling of the regional marine gravity field at the test area of the west Pacific Ocean near Australia. Retracking methods involve both fitting and threshold retracking algorithms, which are specifically developed based on the waveform features of Jason-1 GM and Cryosat-2 LRM from this study. Unknown parameters estimated from waveform retracking are analysed to find their error characteristics. Retracking results provide the optimised data sources for regional gravity field and mean sea surface recovery. The methodologies and techniques traditionally used for local and regional gravity determination are reassessed. Gravity field results for selected regions and with different spatial resolutions are shown and compared to existing models and external data sets.