High-resolution temporal gravity fields from SLR and DORIS using tailored base functions

Time-variable gravity field solutions from satellite missions prior to GRACE are of limited applicability in climate studies, due to their low spatial resolution. To overcome this disadvantage, we developed a novel parametrization in which the temporal changes of the gravity field are represented by a finite number of spatial patterns tailored to the expected signal power. These patterns are identified by an EOF analysis applied to the GRACE and GRACE Follow-On solutions. Using such tailored base functions does not break down the limits of the tracking technique, but allows to isolate large-scale mass variations with the full GRACE resolution, while the parameter space is kept extremely tight. 

In a previous publication, this approach has been successfully applied to compute a GRACE-like time series from five SLR satellites going back to 1992. To further enhance this solution, we now turned towards the DORIS constellation from which we processed data from ten satellites at altitudes up to 1000 km. It was found that our parametrization is highly suitable also for the DORIS system and results in a time series that agrees well with that from SLR. Such agreement is found even for the very first years when the DORIS solution is occasionally based on one single satellite. We note that we include the estimation of thermosphere model scaling parameters that can help in understanding neutral density change.

The contribution will provide details of our DORIS processing and present total water storage maps and mass balances for selected regions from DORIS, SLR and from the combination of both techniques. We believe our results will contribute to long-term mass studies concerned with sea-level change, ice mass loss at high latitudes or water storage changes in large river basins. In addition, it will be shown that the presented time series can improve the force models for precise orbit determination at higher altitude. For example, a dynamic reconstruction of Jason-3 orbits from kinematic positions reveals that the SLR/DORIS solution performs competitively in this task when compared to the frequently applied EIGEN-GRGS.RL04 model, with some advantage in the later years when the EIGEN model provides pure predictions.