Satellite Gravimetry: Realization and Further Prospects

Since the time of Kepler, Newton, and Huygens in the 17th century, geodesy has been concerned with determining the Earth’s figure, orientation, and gravitational field. The dawn of the space age in 1957 gave rise to a new branch of the discipline: satellite geodesy. It was only through the use of satellites that geodesy truly became a global science - oceans ceased to be barriers, and the Earth could be observed and measured as an integrated whole using consistent datasets. Particular attention was devoted to resolving the spatial structure of the Earth’s gravity field and, eventually, its temporal variations. Knowledge of the gravity field forms a natural link to the study of the Earth’s interior, the circulation of the oceans, and, more recently, the climate system. Today, changes in the gravity field provide key insights into climate change, including ice mass loss in Greenland and Antarctica, sea-level rise, and broader changes in the global water cycle. These advances have only been possible through the use of highly sophisticated gravity-field satellites, a field known as satellite gravimetry.During the first four decades of space exploration, satellite gravimetry relied primarily on analyzing the orbital motion of satellites. Due to the uneven global distribution of tracking stations, initially limited measurement accuracy, and shortcomings in early analysis models, reconstructing global models of the Earth’s gravity field posed a major challenge. A decisive breakthrough came in the final decade of the 20th century with the transition from passive satellites to missions equipped with dedicated, high-precision instrumentation for gravity-field determination. The Vening Meinesz lecture will review the historical background of satellite gravimetry as well as mission objectives, measurement principles and implementation challenges of modern gravity missions like CHAMP, GRACE, GOCE, and GRACE-FO. It will further highlight selected scientific results and applications from these missions and outline opportunities for the next generation of geodesists arising from future gravity field missions currently under development.Further reading: Frank Flechtner, Christoph Reigber, Reiner Rummel, and Georges Balmino (2021): Satellite Gravimetry: A Review of Its Realization, Surveys in Geophysics, 42:1029–1074, https://doi.org/10.1007/s10712-021-09658-