TY - JOUR

T1 - PPP-based Swarm kinematic orbit determination

AU - Ren, Le

AU - Schön, Steffen

N1 - Acknowledgements: This project is part of the Consistent Ocean Mass Time Series from LEO Potential Field Missions (CONTIM) and funded by the Deutsche Forschungsgemeinschaft (DFG) under the SPP1788 Dynamic Earth which is gratefully acknowledged.We would like to thank ESA for providing Swarm data. The Swarm kinematic orbits have been made available by ESA, AIUB and IfG, TU Graz. GPS orbits and clocks have been obtained from the Center for Orbit Determination in Europe (CODE). The SLR residuals are kindly provided by Anno Löcher of Institute of Geodesy and Geoinformation, University of Bonn. TU Delft is also very appreciated for providing the PCV maps. The support of all these institutions is gratefully acknowledged. The publication of this article was funded by the open-access fund of Leibniz Universität Hannover. The topical editor, Monika Korte, thanks two anonymous referees for help in evaluating this paper

PY - 2018/9/20

Y1 - 2018/9/20

N2 - The Swarm mission of the European Space Agency (ESA) offers excellent opportunities to study the ionosphere and to provide temporal gravity field information for the gap between the Gravity Recovery and Climate Experiment (GRACE) and its follow-on mission (GRACE-FO). In order to contribute to these studies, at the Institut für Erdmessung (IfE) Hannover, a software based on precise point positioning (PPP) batch least-squares adjustment is developed for kinematic orbit determination. In this paper, the main achievements are presented. The approach for the detection and repair of cycle slips caused by ionospheric scintillation is introduced, which is based on the Melbourne-Wübbena and ionosphere-free linear combination. The results show that around 95% of cycle slips can be repaired and the majority of the cycle slips occur on L/2. After the analysis and careful preprocessing of the observations, 1-year kinematic orbits of Swarm satellites from September 2015 to August 2016 are computed with the PPP approach. The kinematic orbits are validated with the reduced-dynamic orbits published by the ESA in the Swarm Level 2 products and SLR measurements. The differences between IfE kinematic orbits and ESA reduced-dynamic orbits are at the 1.5, 1.5 and 2.5 cm level in the along-track, cross-track and radial directions, respectively. Remaining systematics are characterized by spectral analyses, showing once-per-revolution period. The external validation with SLR measurements shows RMSEs at the 4 cm level. Finally, fully populated covariance matrices of the kinematic orbits obtained from the least-squares adjustment with 30, 10 and 1 s data rate are discussed. It is shown that for data rates larger than 10 s, the correlation between satellite positions should be taken into account, for example, for the recovery of gravity field from kinematic orbits.

AB - The Swarm mission of the European Space Agency (ESA) offers excellent opportunities to study the ionosphere and to provide temporal gravity field information for the gap between the Gravity Recovery and Climate Experiment (GRACE) and its follow-on mission (GRACE-FO). In order to contribute to these studies, at the Institut für Erdmessung (IfE) Hannover, a software based on precise point positioning (PPP) batch least-squares adjustment is developed for kinematic orbit determination. In this paper, the main achievements are presented. The approach for the detection and repair of cycle slips caused by ionospheric scintillation is introduced, which is based on the Melbourne-Wübbena and ionosphere-free linear combination. The results show that around 95% of cycle slips can be repaired and the majority of the cycle slips occur on L/2. After the analysis and careful preprocessing of the observations, 1-year kinematic orbits of Swarm satellites from September 2015 to August 2016 are computed with the PPP approach. The kinematic orbits are validated with the reduced-dynamic orbits published by the ESA in the Swarm Level 2 products and SLR measurements. The differences between IfE kinematic orbits and ESA reduced-dynamic orbits are at the 1.5, 1.5 and 2.5 cm level in the along-track, cross-track and radial directions, respectively. Remaining systematics are characterized by spectral analyses, showing once-per-revolution period. The external validation with SLR measurements shows RMSEs at the 4 cm level. Finally, fully populated covariance matrices of the kinematic orbits obtained from the least-squares adjustment with 30, 10 and 1 s data rate are discussed. It is shown that for data rates larger than 10 s, the correlation between satellite positions should be taken into account, for example, for the recovery of gravity field from kinematic orbits.

UR - http://www.scopus.com/inward/record.url?scp=85053872083&partnerID=8YFLogxK

U2 - 10.5194/angeo-36-1227-2018

DO - 10.5194/angeo-36-1227-2018

M3 - Article

AN - SCOPUS:85053872083

VL - 36

SP - 1227

EP - 1241

JO - Annales geophysicae

JF - Annales geophysicae

SN - 0992-7689

IS - 5

ER -