Calculation of daily variations of the Earth's gravity field at GFZ
There has been a lot of improvement and development at GFZ during the past few weeks concerning the sensitivity of the applied Kalman process, enhancement of the data screening, reduction of outliers etc and a new daily time series of variations of the Earth's gravity field is well under its way to be delivered for evaluation purposes (e.g. to our colleagues from hydrology), soon.
The approach that we follow is an inverse mapping of the measured relative GRACE twin accelerations to a surface (water) layer at equi-areal grid tiles. As there is an abstraction from global signal resolution (physically limited by the number of satellite revolutions per day) towards regional emphasis into the nearby grid tiles next to the satellite's ground track, we expect to capture higher wavelength's of the gravity field for these areas, as well. Current challenges are the reliability/stability of the process to obtain fully automatized time-series.
Figures 1-3 demonstrate:
the daily variation with ground tracks,
the total temporal variation with respect to the static background model
and the respective standard deviations
Note the separation of land-ocean since the GRACE Level-1B Atmosphere and Ocean de-aliasing Model (AOD1B) signal has been subtracted from the observed accelerations and corresponding a-priori error covariances for continental hydrology are included in the Kalman-update.
Furthermore, a future internal meeting is scheduled at TU Graz in order to discuss (dis) accordance in our modeling and solutions.
