In the context of global climate research, knowledge about mass redistribution in the Earth system has become a vital source of information to solve recent scientific questions. Mass redistribution causes small changes in the Earth’s gravity field. Observing these variations helps to better understand underlying processes and their interdependencies.
In contrast to other observation methods, satellite gravimetry is able to observe gravity changes on a global scale with homogenous accuracies. The satellite mission Gravity Recovery and Climate Experiment (GRACE) is currently the only dedicated satellite mission to provide accurate gravity observations. The installation of an operational gravity field service to support emergency management tasks is envisaged for the near future. Currently this system only relies on GRACE observations. An important aspect of an operational service is to provide reliable and safe information. This can be achieved by including independent observation types.
Recent investigations showed that it is possible to derive at least large scale gravity changes from high-low satellite-to-satellite tracking (hlSST) data. The method uses Global Positioning System (GPS) observations made on board low Earth orbit satellites to accurately determine the satellite trajectory. These position estimates are then utilized to estimate the Earth’s gravity field. The measurement quality of GPS observations limits the achieved results in terms of accuracy as well as spatial and temporal resolution. To provide a reasonable supplement to GRACE observations, the hlSST observations must be augmented by additional observation methods. Especially an improved spatial resolution is of great interest for research topics based on gravity field measurements.
Loading displacement observed by permanently operating GPS stations on the continents can be used to observe regional variations of the Earth’s gravity field and subsequently quantify mass redistribution. By combining satellite data and terrestrial observations of station dis-placements, it is possible to improve the spatial resolution of the resulting gravity field information, at least for continental areas with a good station distribution.
The added value for continental applications, i.e. the terrestrial hydrological water cycle or ice mass balance, is undoubtedly high. Currently, loading observations are mostly used in regional applications to answer specific research questions or for validation purposes. The combination on global scale with hlSST data to provide gravity field information for any application and independent from dedicated satellite missions, like GRACE, is new and innovative.
Results featuring higher accuracy and spatial resolution compared to hlSST-only solutions can be expected. They will provide a more detailed and valuable source of information about mass redistribution in the Earth system and thus contribute to international efforts towards a better understanding of our climate and the environment.
A future inclusion of these observations into an operational gravity field service will improve its quality, reliability and most importantly, it makes the system less prone to failure of one of the observation techniques.
Graz University of Technology
Graz University of Technology
Univ.-Prof. Dr.-Ing. Torsten Mayer-Gürr