Real-time precise GNSS satellite orbit and clock products are the prerequisite of real-time GNSS-... more Real-time precise GNSS satellite orbit and clock products are the prerequisite of real-time GNSS-based applications. To obtain real-time GNSS satellite orbit and clock, three approaches exist currently, namely, the prediction-estimation approach, the prediction-correction approach and the estimation approach. Different from the former two approaches, which are based on the predicted orbit, the last approach estimates orbit and clock in an integrated way, thus it is the most rigorous one. However, the simultaneously estimation of both orbit and clock parameters makes it very time-consuming. In this contribution, the extended Kalman filter with parallel computation proposed for real-time GPS satellite clock estimation (Gao, et al., 2017) is introduced to improve the computational efficiency. In the introduced method, the epoch observations are processed sequentially and the covariance update process is accelerated with the Open Multi-Processing. With observation data from about 70 globally distributed stations spanning days 001-003 of 2018, the real-time GPS orbit and clock are estimated for validation. The epoch average processing time of the introduced method achieves around 2.9 s on average with 16 CPU cores, while that of the traditional method without Open Multi-Processing is about 4.1 s. When compare the estimated orbit and clock to the IGS final products, the daily constellation-mean RMS of orbit achieve 2.7, 5.7, 4.9 cm for the radial, along-track
Precise orbit determination for GRACE with zero-difference kinematic method
Chinese Science Bulletin, 2010
Thanks to the high performance of the spaceborne GPS receiver and the availability of precise IGS... more Thanks to the high performance of the spaceborne GPS receiver and the availability of precise IGS orbit and clock products, zero-difference kinematic precise orbit determination (POD) has been turned out to be a new effective method in orbit determination for the LEO satellites. Zero-difference kinematic POD, which is based on the GPS measurements only from the spaceborne GPS receiver, does not depend on the force models and orbit design. From this point of view, kinematic POD is suitable for the Earth observation satellites at very low altitudes, such as CHAMP, GRACE and GOCE, etc. This paper first reviews the basic zero-difference GPS observation model. Then a modified data quality control scheme is put forward. Finally, a block-wise least squares algorithm, which first separates the parameters into several groups and then solves the parameters by elimination and back-substitution, is discussed and proposed for the kinematic orbit determination. With the above algorithms, we developed kinematic POD software to solve the orbit suitable for one-week GRACE observations. Comparisons with the published Rapid Science Orbit (RSO) indicate that, using our approach to determine the orbit, the accuracy in the radial direction can achieve 3–4 cm for GRACE-A, and 3–5 cm for GRACE-B.
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Papers by Shoujian Zhang