GFZ Kalman-filtered daily GRACE gravity field solutions, computed on standard 2ºx2º equi-angular grids are now available for internal evaluation and verification. The grids are recursively predicted and consecutively updated by Poisson's integral over a set of radial basis functions in equi-areal surface tiles of available GRACE K-Band data and reduced dynamic GRACE orbits.
The entire available GRACE data has been reprocessed based on the GRACE microwave ranging data, GPS orbits and clocks and auxiliary data such as star camera and accelerometry measurements. During our processing dynamic GRACE orbits are iteratively fitted towards GRACE GPS high-low phase and low-low K-band measurements. Together with the ranging system they complement to full gradient potential differences in line-of-sight that can be numerically integrated from gravity functions on surface tiles. The inverse operation for surface density layer estimates is then stabilized by a stochastic prediction step and the measurement update within a Kalman filter. For the prediction step the residual signal covariances from geophysical background models for the Atmosphere (ECMWF), the Ocean (OMCT) and Hydrology (WGHM) have been used.
Tests of the daily grids that will be conducted in the following weeks comprise GPS permanent station loading coherence, correlations in hydrological basins with available hydrological models, comparisons of individual spherical harmonic coefficients (e.g. degree 2) with respective SLR time-series and comparisons to in-situ ocean bottom pressure recorder data. For selected individual catchments aggregated values are generated and compared to specific river discharge and flow volume estimates.
Besides the processing of these “historical data” the gravity service is taking it's next step towards consistent Near Real Time processing capability. For this we have replaced the standard Earth orientation data from the International Earth Rotation and Reference Systems Service (IERS) with the prediction products and our GFZ-derived GPS constellations with the ultra rapid orbits and clocks from the Center for Orbit Determination in Europe (CODE). First test results with NRT-latencies are expected soon.
