Inhaltsbereich
Geotechnologien II: "Improved GRACE Level-1 and GRACE Level-2 Products"
Improved GRACE Level-1 and Level-2 products and their validation against ocean bottom pressure
duration: Sep 2005 - Aug 2008
In cooperation with: TU München, Uni Bonn, TU Dresden, AWI Bremerhaven
supported by: Geotechnologien research program, joint effort of German Research Council (DFG) and Ministry of Education and Research (BMBF)
This project intends to achive an advanced scientific benefit from the satellite gravity field mission GRACE by increasing the accuracy of its Level-1 and Level-2 products. This is reached through an integrated performance assessment of the gravity field sensor system and through an updated atmosphere-ocean de-aliasing product as well as the application of a new atmospheric tide model. Subsequently, alternative approaches to generate gravity field solutions are implemented and the resulting monthly mean solutions are evaluated against in-situ ocean bottom pressure observations.
In particular, Section 1.5 is involved in updating the atmosphere-ocean dealiasing product by replacing the formerly used barotropic ocean model with the Ocean Model for Circulation and Tides (OMCT). Acquisition of latest available atmospheric data from the European Centre for Medium-Range Weather Forecasts (ECMWF) and preparation as forcing fields for OMCT has been fully automated in order to allow the calculation of ocean mass anomalies with 3 days latency only. Currently, 6 hourly ocean mass anomalies in terms of spherical harmonics are released bi-weekly to the GRACE project via the ISDC data portal of GFZ Potsdam.
Contact: Prof. Maik Thomas, Dr. Henryk Dobslaw
- Figure 1: Ocean Mass anomalies are obtained by means of simulations with the globally defined Ocean Model for Circulation and Tides (OMCT), consistently forced with ECMWF atmospheric data and continental runoff from a hydrological model.
In parallel, OMCT simulations are used to assess the impact of various processes on ocean mass anomalies, as, e.g., due to continental freshwater fluxes and the ocean response to atmospheric tides, in order to evaluate their impact on the gravity field processing in terms of potential aliasing and their observability within the monthly mean gravity fields.
- Figure 2: Global pattern of the semidiurnal atmospheric tide as derived from 3 hourly resolved ECMWF forecast data (left) and corresponding ocean response as simulated with OMCT (right).
Additionally, OMCT and Jason 1 data have been applied to validate recent GRACE monthly solutions over the oceans. By means of cross comparisons, GRACE gravity are found to provide reliable ocean mass anomalies down to 500 km regional averages. Correlations of up to 0.8 are apparent in various regions of the Southern Ocean as well as in the North Pacific.
- Figure 3: Monthly mean mass anomalies derived from three different datasets for June 2005: based on GRACE gravity field observations (top left), derived from sterically corrected Jason 1 satellite altimetry (top right) and ocean bottom pressure as simulated with OMCT.
