Abstract
Conventional relative kinematic positioning is difficult to be applied in the polar region of Earth since there is a very sparse distribution of reference stations, while precise point positioning (PPP), using data of a stand-alone receiver, is recognized as a promising tool for obtaining reliable and accurate trajectories of moving platforms. However, PPP and its integer ambiguity fixing performance could be much degraded by satellite orbits and clocks of poor quality, such as those of the geostationary Earth orbit (GEO) satellites of the BeiDou navigation satellite system (BDS), because temporal variation of orbit errors cannot be fully absorbed by ambiguities. To overcome such problems, a network-based processing, referred to as precise orbit positioning (POP), in which the satellite clock offsets are estimated with fixed precise orbits, is implemented in this study. The POP approach is validated in comparison with PPP in terms of integer ambiguity fixing and trajectory accuracy. In a simulation test, multi-GNSS (global navigation satellite system) observations over 14 days from 136 globally distributed MGEX (the multi-GNSS Experiment) receivers are used and four of them on the coast of Antarctica are processed in kinematic mode as moving stations. The results show that POP can improve the ambiguity fixing of all system combinations and significant improvement is found in the solution with BDS, since its large orbit errors are reduced in an integrated adjustment with satellite clock offsets. The four-system GPS+GLONASS+Galileo+BDS (GREC) fixed solution enables the highest 3D position accuracy of about 3.0 cm compared to 4.3 cm of the GPS-only solution. Through a real flight experiment over Antarctica, it is also confirmed that POP ambiguity fixing performs better and thus can considerably speed up (re-)convergence and reduce most of the fluctuations in PPP solutions, since the continuous tracking time is short compared to that in other regions.
Highlights
The GNSS precise kinematic positioning over the polar regions of Earth has always been an important topic, as its trajectory is essential information for any observing and monitoring system via mobile platforms, for example, for airborne gravimetry [1].Usually, the traditional relative kinematic positioning (RKP), which requires reference stations nearby, is applied in order to remove most of the common biases
This paper focuses on kinematic positioning over Antarctica with multi-GNSS observations
The conventional precise point positioning (PPP) and its ambiguity fixing in Antarctic stations are demonstrated to be negatively influenced by the poor orbit quality of the BeiDou navigation satellite system (BDS) satellites
Summary
The GNSS (global navigation satellite system) precise kinematic positioning over the polar regions of Earth has always been an important topic, as its trajectory is essential information for any observing and monitoring system via mobile platforms, for example, for airborne gravimetry [1]. The accuracy of GPS, GLONASS and Galileo final orbit and clock products turns out to be at the same level, since their MGEX (Multi-GNSS Experiment) tracking stations are globally and evenly distributed, whereas there are only about 71 stations with Beidou observations, mainly distributed in Europe and Asia-pacific areas, and only two stations named CAS1 and DAV1 in Antarctica. In order to get rid of the disadvantage of RKP and PPP, a method named precise orbit positioning (POP) [8] is applied to process the Antarctica data This is, in principle, a network solution with fixed satellite orbits, where satellite clock offsets are estimated with a global or large regional reference network instead of a few nearby reference stations.
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