Improved representations of the Mediterranean Geoid within the GEOMED 2 project. Contributions of local gravity, GOCE and Cryosat2 data

The Mediterranean Sea has always been a lab for geosciences, given its geodynamic peculiarities, the large short-scale variations of the gravity field and the complex circulation. Within the GEOMED 2 project, new improved representations of the Mediterranean marine geoid have been deemed as necessary, so that the Mean Dynamic sea surface Topography (MDT) and the circulation can be modelled with higher accuracy and resolution.

This is possible given the availability of gravity-field related satellite data from GOCE, improved models of the land topography and bathymetry and the compilation of a Mediterranean-wide gravity database. The data employed within GEOMED 2 for the determination of the marine geoid are land and marine gravity data, GOCE/GRACE based Global Geopotential Models and a combination of MISTRAL and SRTM/bathymetry terrain models.

The processing methodology will be based on the well-known remove-compute-restore method following both stochastic and spectral methods for the determination of the geoid. Classic least-squares collocation (LSC) with errors has been employed investigating both spherical and planar analytical covariance functions models, while fast Fourier transform (FFT)-based techniques have provided the geoid estimation in the frequency domain.

In this work, the pre-processing steps consisting in merging and validating all the available gravity observations for the wider Mediterranean are presented and discussed. Furthermore, the latest basin-wide geoid models are estimated from the validated gravity data using all outlined methodologies. The so-determined geoid models are validated against GPS/Levelling observations over land areas, with special emphasis on the coastal to near-coastal regions, as well as satellite altimetry observations from the Jason2, Envisat and Cryosat2 missions.