Abstract
The GNSS Occultation Sounder instrument onboard the Chinese meteorological satellite Fengyun-3C (FY-3C) tracks both GPS and BDS signals for orbit determination. One month’s worth of the onboard dual-frequency GPS and BDS data during March 2015 from the FY-3C satellite is analyzed in this study. The onboard BDS and GPS measurement quality is evaluated in terms of data quantity as well as code multipath error. Severe multipath errors for BDS code ranges are observed especially for high elevations for BDS medium earth orbit satellites (MEOs). The code multipath errors are estimated as piecewise linear model in 2{^{circ }}times 2{^{circ }} grid and applied in precise orbit determination (POD) calculations. POD of FY-3C is firstly performed with GPS data, which shows orbit consistency of approximate 2.7 cm in 3D RMS (root mean square) by overlap comparisons; the estimated orbits are then used as reference orbits for evaluating the orbit precision of GPS and BDS combined POD as well as BDS-based POD. It is indicated that inclusion of BDS geosynchronous orbit satellites (GEOs) could degrade POD precision seriously. The precisions of orbit estimates by combined POD and BDS-based POD are 3.4 and 30.1 cm in 3D RMS when GEOs are involved, respectively. However, if BDS GEOs are excluded, the combined POD can reach similar precision with respect to GPS POD, showing orbit differences about 0.8 cm, while the orbit precision of BDS-based POD can be improved to 8.4 cm. These results indicate that the POD performance with onboard BDS data alone can reach precision better than 10 cm with only five BDS inclined geosynchronous satellite orbit satellites and three MEOs. As the GNOS receiver can only track six BDS satellites for orbit positioning at its maximum channel, it can be expected that the performance of POD with onboard BDS data can be further improved if more observations are generated without such restrictions.
Highlights
For many low earth orbit (LEO) scientific missions, such as the geodetic and oceanographic missions designed for measuring global sea level, determining the earth’s gravity field, or sensing the atmosphere using occultation signals, the orbit precision is often required at the centimeter level, which makes precise orbit determination (POD) challenging
Studies of the BeiDou Navigation Satellite system (BDS) multipath error have become of particular interest in recent years due to the presence of satellite-related code multipath biases in comparison with other GNSS systems, which can be well modeled as piecewise linear or polynomials associated with elevation angles for medium earth orbit satellites (MEOs) and IGSOs based on BDS data from ground stations (Wanninger and Beer 2015; Yang et al 2016)
In the first case with geosynchronous orbit satellites (GEOs) included in the combined POD processing, the linear combination (LC) residual root mean square (RMS) values of BDS GEOs are exceptionally larger than the IGSOs and MEOs, and the RMS errors of C02 and C03 satellites even reach to 36 and 77 mm, respectively, which is very similar with the first case of BDSbased POD
Summary
For many low earth orbit (LEO) scientific missions, such as the geodetic and oceanographic missions designed for measuring global sea level, determining the earth’s gravity field, or sensing the atmosphere using occultation signals, the orbit precision is often required at the centimeter level, which makes precise orbit determination (POD) challenging. These results indicate that in its service area, BDS can provide comparable precisions in position and ZTD estimates with respect to GPS All these studies are carried out using ground-based data, while the quality of onboard BDS data and its contribution to LEO POD have not been investigated yet. The Chinese FY-3C satellite, designed for collecting atmospheric data for intermediate- and long-term weather forecasting and global climate research (Bi et al 2012), was launched in September 2013 with a sun-synchronous, nearcircular, near-earth orbit at an altitude of 836 km For both POD and occultation observing purposes, FY-3C carries a GNSS Occultation Sounder (GNOS) instrument onboard. Precise orbit determination of the Fengyun-3C satellite using onboard
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