engleski

Gravimetric geoid model development in the Mediterranean Sea within the Geomed2 project

It is well-known that the Mediterranean Sea is challenging both in terms of geoid and Mean Dynamic Ocean Topography (MDOT) determination due to its geodynamic and oceanic features. Poor gravity data coverage and their outdated nature, along with the fact that the gravity and geoid slopes in the Mediterranean reach significant values with high variability, make geoid determination a cumbersome exercise stretching the numerical capabilities of all related methodologies and algorithms. Likewise, its semi-enclosed nature and the existence of many islands and isles make the determination of the Mediterranean MDOT quite problematic given that all filtering methods applied in the open ocean do not give reasonable results, while altimetry data themselves suffer from land contamination. On the other hand, both geoid and the MDOT are mandatory to support applications in geosciences, hence the determination of improved representations of the Mediterranean marine geoid and its circulation have been deemed as necessary. The GEOMED 2 project aims at the determination of a high-accuracy and resolution marine geoid based on 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 are land and marine gravity data, the latest satellite only and combined GOCE/GRACE based Global Geopotential Models and a combination of MISTRAL, EMODnet and SRTM/bathymetry terrain models. The processing methodology was based on the well-known remove-compute-restore method following both stochastic and spectral methods for the determination of the geoid. the classic fashion of least-squares collocation (LSC) with errors has been employed investigating both spherical and planar analytical covariance functions models, along with Fast Fourier transform (FFT)-based techniques, the KTH approach based on Least-Squares Modification of Stokes (LSMS) and Fast Collocation. In this work, the pre-processing steps consisting of merging and validating all the available gravity observations for the wider Mediterranean are presented and discussed. Furthermore, the latest basin-wide geoid models were estimated from the gravity data using all outlined methodologies and validated against GPS/Leveling data and newly acquired gravity observations.

Mediterranean; geoid; FFT; LSC; FastCol; KTH

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