COVER - Combination of observation techniques for climate and geophysical research

Since the beginning of the 21st century special attention is placed on the computation of long-term mass changes in the system Earth from time-variable gravity. It reflects a key quantity in Earth-, climate and geophysical research and enables the monitoring of geophysical systems. Especially the gravity field mission GRACE, which was in orbit from 2002 till 2017, and its successor mission GRACE-Follow On (launched in 2018) have fundamentally changed our understanding of mass transport in the Earth system. However, due to their mission design, both are not especially sensitive to the very long wavelengths of the gravity field. In contrast, satellite laser ranging (SLR) represents an observation technique which is predestined for the determination of the long-wavelength part of Earth’s gravity field. Therefore, the project COVER has the objective to develop a methodology to allow for a combination of both observation techniques taking into consideration random and systematic errors. The foundation of these enhanced methodology will be the implementation of an independent SLR processing chain in the existing and well recognized GRACE processing software package GROOPS. This is a key point since it ensures a consistent processing of SLR and GRACE/GRACE-FO. Regarding the SLR processing the project has an additional objective in mind. The first SLR observations were performed in 1964 by tracking the Beacon-B satellite. Since then, the observation technique has become more and more sophisticated and has now the capability to track navigation and geostationary satellites with millimeter accuracy. However, through the steadily increasing number of satellites in orbit the risk of collisions with space debris objects is apparent. In general, these observations are performed by ground-based radar stations. However, since the accuracy of these observation technique is limited, several studies in the past have attempted to show that SLR has the capability to make an important contribution regarding the tracking of such uncooperative targets. The biggest barrier nowadays is still the availability of accurate orbit predictions. To address this issue, the implementation of the SLR chain will directly be support by the local SLR station Graz-Lustbühel through real-time measurements to space debris objects using the self-produced orbit predictions. Based on the incorporation of cutting-edge force modelling, the consideration of systematic observation errors and the feedback of the SLR station the orbit predictions should be as accurate as possible to enable a successful tracking of space debris objects. With that in mind, the project COVER is intended to make a significant contribution to more safety and security in space in the future.