Heidelberg 2022 – scientific programme

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GR: Fachverband Gravitation und Relativitätstheorie

GR 2: Classical Theory

GR 2.6: Talk

Monday, March 21, 2022, 17:40–18:00, GR-H2

Gravitational field recovery via inter-satellite redshift measurements — •Jan Hackstein, Eva Hackmann, Claus Lämmerzahl, and Dennis Philipp — Center of Applied Space Technology and Microgravity, Bremen, Germany

Satellite gravimetry is a promising technique to monitor global changes in the Earth system. High-precision atomic clocks are already being compared to measure physical heights in terrestrial gravimetry. In relativistic gravity, a clock comparison is sensitive to the clocks’ positions and relative velocity in the gravity field. Thus, clocks are an ideal tool to investigate the Earth’s gravity field. To cover the whole Earth, orbiting satellites can be equipped with clocks and observed by terrestrial ground stations. One important obstacle for Earth-satellite gravimetry, however, is the low measurement accuracy of a satellite’s velocity, which enters into the redshift via the Doppler effect. Here we follow an alternative approach without absolute velocity measurements based on the framework of general relavity. We consider an idealised satellite setup in the Schwarzschild spacetime where the monopole moment is recovered from pairwise redshift measurements between multiple satellites equipped with clocks. We investigate whether or not the redshift between two satellites can be retrieved as a function depending only on relative observables between the satellites. This method promises a higher accuracy for gravity field recovery by bypassing the Doppler effect. We compare the results and error estimates of these inter-satellite measurements with conventional Earth-satellite measurements and conclude with future applications of this theoretical setup.