GRACE-FO precise orbit determination and gravity recovery
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ORIGINAL ARTICLE
GRACE‑FO precise orbit determination and gravity recovery Z. Kang1 · S. Bettadpur1 · P. Nagel1 · H. Save1 · S. Poole1 · N. Pie1 Received: 13 September 2019 / Accepted: 4 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The gravity recovery and climate experiment follow-on (GRACE-FO) satellites, launched in May of 2018, are equipped with geodetic quality GPS receivers for precise orbit determination (POD) and gravity recovery. The primary objective of the GRACE-FO mission is to map the time-variable and mean gravity field of the Earth. To achieve this goal, both GRACE-FO satellites are additionally equipped with a K-band ranging (KBR) system, accelerometers and star trackers. Data processing strategies, data weighting approaches and impacts of observation types and rates are investigated in order to determine the most efficient approach for processing GRACE-FO multi-type data for precise orbit determination and gravity recovery. Two GPS observation types, un-differenced (UD) and double-differenced (DD) observations in general can be used for GPSbased POD and gravity recovery. The GRACE-FO KBR observations are mainly used for gravity recovery, but they can be also used for POD to improve the relative orbit accuracy. The main purpose of this paper is to study the impacts of the DD, UD and KBR observations on GRACE-FO POD and gravity recovery. The precise orbit accuracy is assessed using several tests, which include analysis of orbital fits, satellite laser ranging residuals, KBR range residuals and orbit comparisons. The gravity recovery is validated by comparing different gravity solutions through coefficient-wise comparison, degree difference variances and water height variations over the whole Earth and selected area and river basins. Keywords GRACE-FO · GPS · KBR · SLR residuals · Precise orbit determination · Gravity recovery
1 Introduction The gravity recovery and climate experiment follow-on (GRACE-FO) mission is a joint project between the National Aeronautics and Space Administration (NASA) and the GeoForschungZentrum (GFZ). The primary objective of * Z. Kang [email protected] S. Bettadpur [email protected] P. Nagel [email protected] H. Save [email protected] S. Poole [email protected] N. Pie [email protected] 1
Center for Space Research, University of Texas at Austin, 3925 W. Braker Lane, Suite 200, Austin, TX 78759‑5321, USA
the GRACE-FO mission is to map the time-variable and mean gravity field of the Earth (Tapley et al. 2005; Flechtner et al. 2015; Landerer et al. 2019; Kornfeld et al. 2019). The twin GRACE-FO (GRACE-C and GRACE-D) satellites were launched on May 22, 2018, into near polar orbits with an initial altitude of about 500 km. For the precise orbit determination (POD) and gravity field recovery, the GRACE-FO satellites are equipped with several scientific instruments: geodetic quality GPS receivers, accelerometers, star trackers, K-band ranging (KBR) system, laser ranging interferometer (LRI) and laser retroreflect
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