Abstract
Abstract. 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 L2. 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.
Highlights
The Swarm mission was launched on 22 November 2013 and is the first constellation of satellites of the European Space Agency (ESA) to study the dynamics of the Earth’s magnetic field and its interaction with the Earth system (FriisChristensen et al, 2008)
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
All the three satellites are equipped with a set of six core instruments: Absolute Scalar Magnetometer (ASM), Vector Field Magnetometer (VFM), Electric Field Instrument (EFI), Star Tracker (STR), Accelerometer (ACC) and GPS Receiver (GPSR)
Summary
The Swarm mission was launched on 22 November 2013 and is the first constellation of satellites of the European Space Agency (ESA) to study the dynamics of the Earth’s magnetic field and its interaction with the Earth system (FriisChristensen et al, 2008). Schön: PPP-based Swarm kinematic orbit determination using reduced-dynamic and kinematic approaches were reported in van den IJssel et al (2015) and Jäggi et al (2016). This approach is based on the precise point positioning (PPP) technique (Zumberge et al, 1997) This differs from the raw measurements approach by the Institute of Geodesy (IfG) of TU Graz (Zehentner and Mayer-Gürr, 2015), phase-only approach by the Astronomical Institute of University Bern (AIUB) (Jäggi et al, 2016) or the Bayesian weighted least-squares estimator, which is implemented in the GPS High-precision Orbit Determination Software Tools (GHOST) developed at the Deutsches Zentrum für Luft- und Raumfahrt in close cooperation with TU Delft and used for the ESA official orbits (van den IJssel et al, 2015). We first analyse the Swarm GPS receiver data quality and introduce our approach for cycle-slip detection and repair as well as outlier screening
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