The European Space Agency (ESA) Swarm mission is a satellite constellation launched on 22 November 2013 aiming at observing the Earth geomagnetic field and its temporal variations. The constellation consists of two satellites flying in pendulum formation in low earth polar orbits and one satellite flying separately in a higher polar orbit. The three identical Swarm satellites are equipped with high-precision 8-channel dualfrequency Global Positioning System (GPS) receivers, which make the Swarm constellation a good test bed for baseline determination. High-precision baseline determination between low earth orbiting satellites is relevant for e.g. Interferometric Synthetic Aperture Radar (InSAR) research, proximity operations between spacecraft, and possibly gravity field determination. For Swarm, special attention has to be paid to several aspects regarding the baseline determination. These aspects include the synchronization of the GPS observations collected by the GPS receivers on the different Swarm satellites, the determination of inflight frequency-dependent Phase Center Variation (PCV) and Code Residual Variation (CRV) antenna patterns, and half-cycle carrier-phase ambiguity resolution. In addition, a number of GPS receiver modifications were made in the October 2014 to August 2016 time frame, such as changes in the Fieldof- View (FoV), tracking loop bandwidth, and Receiver Independent Exchange Format (RINEX) converter updates. Moreover, the on-board GPS receiver performance is greatly influenced by the seasonal ionospheric scintillation, which is caused by irregular plasma bubbles that mostly occur at equatorial and polar areas. The impact of the factors mentioned above is assessed for baseline determination of the pendulum formation flying Swarm-A and -C satellites. They fly at altitudes lower than Swarm-B and their baseline length varies between 30 and 180 km. The assessment is done for four different periods: August 2014, November 2014, August 2016 and November 2016 - are implemented, respectively. These four periods have been selected to especially study the impact of different levels of ionospheric scintillations (normally low in August and high in November) and GPS receiver modifications. The assessment includes a consistency check between so-called kinematic and reduced-dynamic baseline solutions, a validation of the associated absolute orbit solutions by comparison with Satellite Laser Ranging (SLR) observations, overlap analyses between consecutive baseline solutions, success rate of ambiguity fixing, and analysis of observation residuals. First results indicate the usefulness and importance of the GPS receiver modifications and RINEX converter updates. It is found that the GPS receiver modifications significantly reduce the impact of ionospheric scintillations and improve the baseline determination. Especially, a larger carrier phase tracking loop bandwidth is found to be the most beneficial factor for baseline determination.
|Number of pages||1|
|Publication status||Published - 2017|
|Event||4th Swarm Science Meeting & Geodetic Missions Workshop - Banff, Canada|
Duration: 20 Mar 2017 → 24 Mar 2017
Conference number: 4
|Conference||4th Swarm Science Meeting & Geodetic Missions Workshop|
|Period||20/03/17 → 24/03/17|