Abstract's details
Geomed2: gravimetric versus combined geoid model
CoAuthors
Event: 2017 Ocean Surface Topography Science Team Meeting
Session: The Geoid, Mean Sea Surfaces and Mean Dynamic Topography
Presentation type: Type Poster
Contribution: not provided
Abstract:
The GEOMED 2 project aims at the determination of a high-accuracy and resolution marine geoid model based on the availability of improved models for gravity, thanks to GRACE and GOCE in particular, for land topography and bathymetry, and the compilation of a cleaned-up gravity database of the Mediterranean area based on BGI and SHOM data. GEOMED 2 uses land and marine gravity data, the latest satellite-only and combined GOCE/GRACE based Global Geopotential Models and a combination of MISTRALS, EMODnet and SRTM/bathymetry terrain models in the geoid computation. Computation of a gravimetric geoid of the Mediterranean Sea is challenging due to:
• marine gravity data coverage is poor over several parts of the Med;
• quality of the marine gravity data is not homogeneous (bias, precision);
• data reduction is not at the level achieved over land.
Marine gravity data is not available for large parts of the Mediterranean and consequently a gravimetric geoid solution will be significantly less accurate there. Gravity inferred from altimetry data, or a mean sea surface corrected for mean dynamic topography (i.e., an ‘oceanographic’ geoid model), can be used to fill the gaps. However, ocean dynamic signal always contaminates the derived gravity or geoid, which is why a pure gravimetric solution is preferred.
The effect on the geoid solution of using several altimeter-based datasets, such as DTU10, DTU15 and UCSD V24 gravity, in weighted combinations with the gravimetric data will be evaluated and quantified. To that purpose, test models will be constructed and compared to a gravimetric geoid solution. The (local) uncertainty due to the data gaps, and the subsequent uncertainty in the ocean mean dynamic topography and geostrophic currents, can be estimated via the results of all comparisons. All models are equally compared to drifter-inferred current velocities, which constitutes an independent quality evaluation. This type of evaluation leads to a very detailed quality assessment of the models, notably as a function of spatial scale.
• marine gravity data coverage is poor over several parts of the Med;
• quality of the marine gravity data is not homogeneous (bias, precision);
• data reduction is not at the level achieved over land.
Marine gravity data is not available for large parts of the Mediterranean and consequently a gravimetric geoid solution will be significantly less accurate there. Gravity inferred from altimetry data, or a mean sea surface corrected for mean dynamic topography (i.e., an ‘oceanographic’ geoid model), can be used to fill the gaps. However, ocean dynamic signal always contaminates the derived gravity or geoid, which is why a pure gravimetric solution is preferred.
The effect on the geoid solution of using several altimeter-based datasets, such as DTU10, DTU15 and UCSD V24 gravity, in weighted combinations with the gravimetric data will be evaluated and quantified. To that purpose, test models will be constructed and compared to a gravimetric geoid solution. The (local) uncertainty due to the data gaps, and the subsequent uncertainty in the ocean mean dynamic topography and geostrophic currents, can be estimated via the results of all comparisons. All models are equally compared to drifter-inferred current velocities, which constitutes an independent quality evaluation. This type of evaluation leads to a very detailed quality assessment of the models, notably as a function of spatial scale.