Abstract
Swarm is a European Space Agency (ESA) project that was launched on 22 November 2013, which consists of three Swarm satellites. Swarm precise orbits are essential to the success of the above project. This study investigates how well Swarm zero-differenced (ZD) reduced-dynamic orbit solutions can be determined using space-borne GPS data and optimized pseudo-stochastic pulses under high ionospheric activity. We choose Swarm space-borne GPS data from 1–25 October 2014, and Swarm reduced-dynamic orbits are obtained. Orbit quality is assessed by GPS phase observation residuals and compared with Precise Science Orbits (PSOs) released by ESA. Results show that pseudo-stochastic pulses with a time interval of 6 min and a priori standard deviation (STD) of 10−2 mm/s in radial (R), along-track (T) and cross-track (N) directions are optimized to Swarm ZD reduced-dynamic precise orbit determination (POD). During high ionospheric activity, the mean Root Mean Square (RMS) of Swarm GPS phase residuals is at 9–11 mm, Swarm orbit solutions are also compared with Swarm PSOs released by ESA and the accuracy of Swarm orbits can reach 2–4 cm in R, T and N directions. Independent Satellite Laser Ranging (SLR) validation indicates that Swarm reduced-dynamic orbits have an accuracy of 2–4 cm. Swarm-B orbit quality is better than those of Swarm-A and Swarm-C. The Swarm orbits can be applied to the geomagnetic, geoelectric and gravity field recovery.
Highlights
Root Mean Square (RMS) of Swarm GPS phase residuals is at 9–11 mm, Swarm orbit solutions are compared with Swarm Precise Science Orbits (PSOs) released by European Space Agency (ESA) and the accuracy of Swarm orbits can reach 2–4 cm in R, T and N directions
Swarm is a European Space Agency (ESA) project that was launched on 22 November 2013, which consists of three Swarm satellites
Vector and scalar magnetometers were used on the Swarm satellites to monitor the change of the geomagnetic field; a thermal ion imager and a Langmuir probe were applied to monitor the geoelectric field information; space-borne GPS receivers were used to research the precise orbit determination (POD) and laser retro-reflectors were applied to validate
Summary
Swarm is a European Space Agency (ESA) project that was launched on 22 November 2013, which consists of three Swarm satellites. GPS High precision Orbit determination Software Tools (GHOST) to calculate Swarm zero-differenced reduced-dynamic POD and kinematic POD, the consistency between the two orbits is at 4–5 cm. We study the orbit quality that Swarm orbits can achieve under high ionospheric activity by using optimized pseudo-stochastic pulses based on the ZD reduced-dynamic technique. Space-borne dual-frequency GPS observations and suitable force models are used, especially with the aid of a highly advanced gravity field model, EIGEN-6S4 [16]. This article presents a new POD strategy for all three Swarm satellites using the space-borne dual-frequency GPS data together with reduced dynamic models. The study computes Swarm precise orbits via a ZD reduced-dynamic approach based on Bernese software. The approach combines space-borne GPS observation from Swarm level 1B products released by ESA [17] and suitable force models.
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