Abstract
The Global Navigation Satellite System (GNSS) occultation receiver onboard the China Seismo-Electromagnetic Satellite (CSES) can provide dual-frequency observations for both GPS and BDS-2 satellites. In this study, the data quality and orbit determination performance of the CSES are assessed. Severe data loss of about 30% is observed in GPS P2/L2 data, resulting in only 11% of epochs possessing six to eight useful GPS satellites. Due to fewer channels being allocated for BDS signals, less than 5% of epochs have more than three useful BDS satellites. Precise orbit determination (POD) of CSES is firstly carried out using GPS data. The results indicate that the orbit overlap differences improved from 3.65 cm to 2.8 cm in 3D root mean square (RMS) by antenna phase center correction. CSES orbits are then derived from the BDS only, and combined GPS and BDS data. BDS-based POD indicates that adding BDS geostationary Earth orbit (GEO) satellites could dramatically degrade the orbit accuracy. When excluding BDS GEO satellites, the orbit overlap differences of BDS-based and combined POD are 23.68 cm and 2.73 cm in 3D, respectively, while the differences compared with GPS-based POD are 14.83 cm and 1.05 cm, respectively. The results suggest that the obtained orbit can satisfy centimeter-level requirements. Given that large GPS tracking losses occurred and few channels are allocated for BDS signals, it is expected that POD performance can be further improved by increasing the number of dual-frequency observations.
Highlights
The China Seismo-Electromagnetic Satellite (CSES), known as ZhangHeng-1, was launched on 2 February 2018
The satellite body-fixed (SBF) frame (Figure 1) is defined as follows: the origin is the center of mass, the +Z axis is opposite to the satellite radial direction, the +X axis points to the velocity direction of the satellite and the Y-axis is perpendicular to the Z-axis and the X-axis, completing the right-hand coordinate system
For precise orbit determination (POD) based on Positioning and Navigation Data Analyst (PANDA) products, excluding geostationary Earth orbit (GEO) satellites led to an improvement in both average orbit overlap difference and in the comparison to GPS-based POD, showing significant improvements in all three directions
Summary
The China Seismo-Electromagnetic Satellite (CSES), known as ZhangHeng-1, was launched on 2 February 2018. It is currently located in a 507 km sun-synchronous orbit with a nominal lifetime of. This satellite is China’s first spaceborne platform dedicated to geophysical field measurement and earthquake monitoring by detecting electromagnetic variations in space [1]. As part of the CSES scientific application, ionospheric research and neutral atmospheric inversion require orbit accuracy at centimeter-level. China plans to carry out more low Earth orbit (LEO) scientific missions on a geophysical field for monitoring earthquakes, sensing the atmosphere or determining the Earth’s gravity field. The inversion of the Earth’s gravity field requires an orbit accuracy at centimeter-level
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