Real-Time PPP Based on the Coupling Estimation of Clock Bias and Orbit Error with Broadcast Ephemeris

Pan, Shuguo; Chen, Weirong; Jin, Xiaodong; Shi, Xiaozhong; He, Fan

doi:10.3390/s150717808

Cited by 10 publications

(6 citation statements)

References 14 publications

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“…Then, we map the zenith calibrations to slant sight direction using Global Mapping Function (GMF; Boehm et al, 2006), which is one of the accurate mapping functions in the real-time (Liu et al, 2015;Urquhart et al, 2013). The GMF formula is presented as: Satellite orbit Ultra rapid orbit products (Choi et al, 2012) Satellite clock offsets Broadcast ephemeris (Pan et al, 2015) Satellite and receiver antenna ANTEX PCO + PCV (Montenbruck et al, 2015) Radiation pressure Corrected (Arnold et al, 2015) Earth (5)…”

Section: Tstd Methodsmentioning

confidence: 99%

Tropospheric Delay Correction of VLBI Stations for the Real‐Time Trajectory Determination of the Chang'E‐5 Spacecraft

Zhou

Song

et al. 2022

Radio Science

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The Chang'E‐5 (CE‐5) spacecraft was launched on 24 November 2020 with the purpose to implement unmanned lunar surface sampling and return. Very long baseline interferometry (VLBI) technique played an important role in real‐time precise trajectory determination and attitude determination of the CE‐5 spacecraft in the Earth to Moon transfer, circumlunar, landing, and ascending phases. However, tropospheric delay is one of the main error sources for VLBI observations which has to be corrected accurately for precise trajectory determination. To deal with this error properly, a prediction model (TRO_P) and a method with Global Navigation Satellite System observations (TRO_G) are proposed for tropospheric zenith delay correction for real‐time and 30 min latency trajectory determination of the CE‐5 spacecraft, respectively. The results demonstrate that the mean root mean square (RMS) of residual error of VLBI delay and delay rate for TRO_P are 0.62 ns and 0.75 ps/s at low elevation angle, respectively. Moreover, the improvement for the mean RMS of VLBI delay using TRO_G is 39.5% meaning from 0.43 to 0.26 ns compared with that using the method with meteorological data (TRO_S) at low elevation angle. This study can provide a reference for tropospheric delay calibration for trajectory determination of the spacecraft using VLBI or other techniques.

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Section: Tstd Methodsmentioning

confidence: 99%

Tropospheric Delay Correction of VLBI Stations for the Real‐Time Trajectory Determination of the Chang'E‐5 Spacecraft

Zhou

Song

et al. 2022

Radio Science

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“…It is also well known that the ultrarapid orbits have an internal consistency of better than 5.0cm, which can satisfy the requirements of real-time applications. However, the existing clock extrapolation methods would incur serious accuracy loss because of the discrete nature of satellite clock errors [18]. The ultra-rapid clock accuracy is not well enough, and it is the key problem of the current realtime precise point positioning (PPP) [19].…”

Section: Introductionmentioning

confidence: 99%

An Improved QZSS Satellite Clock Offsets Prediction Based on the Extreme Learning Machine Method

Zhou

Zhu

et al. 2020

IEEE Access

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The Japanese Quasi-Zenith Satellite System (QZSS) has been developed as a GPS (Global Positioning System) complementary system to improve positioning accuracy in the Asia-Pacific region. However, the accuracies of ultra-rapid predicted clocks are not high enough for real-time applications, so it is still a challenge problem. This paper focuses on the clock predictions of the new QZSS constellation. Based on the QZSS clock periodic characteristics, an improved clock prediction method combining the spectrum analysis model (SAM) and extreme learning machine (ELM) is proposed with abbreviation as iELM. The key parameters of iELM are selected carefully including the number of hidden layer nodes and activation function. Further, the input length of the iELM network is optimized and discussed thoroughly. For the purpose of assessing the performance of the proposed algorithm, the clock prediction accuracies are compared among GBU-P (the ultra-rapid predicted orbits/clocks provided by GFZ (Deutsches GeoForschungsZentrum)), SAM and iELM methods. It is demonstrated that iELM keeps in a high level of accuracy below 1.0ns with the predicted time increasing from 0 to 18h, and a little larger during the next six hours. And the QZO (Quasi-Zenith Orbit) satellites perform better than GEO (Geostationary Earth Orbit) satellite. Furthermore, precise point positioning (PPP) for both static and kinematic modes are experimentally studied for 13 IGS (International GNSS (Global Navigation Satellite System) Service) MGEX (Multi-GNSS Experiment) stations in the longitude range between 100°E and 180°E. In the static PPP mode, the iELM method is verified to be effective for the GPS/QZSS constellation as positioning accuracy is improved by 28.3%, 57.7% and 47.4% on average in the east, north and up component with respect to GPS/QZSS GBU-P results. Nearly 70.0% stations achieve sub-decimeter accuracy in the vertical component. As for the kinematic PPP, the iELM method based on GPS/QZSS observations performs much better than the others for shorter convergence time and better positioning accuracy. Compared with GPS/QZSS GBU-P, iELM takes at most a half time to get convergence, and the accuracy is enhanced by 27.6%, 23.7% and 13.9% on average in the east, north and up direction respectively.

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“…However, the post-processing products are available only after one day or a couple of hours later, which is not very acceptable for real-time users. In addition, it is well known that the clock products absorb partly the errors of predicted orbits, particularly errors of the line-of-sight (LOS) direction [ 23 , 24 , 25 ]. Therefore, it is more reasonable to assess orbit and clock residual error as a whole directly from a user’s perspective.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Wide-Lane Ambiguities Derived from Geometry-Free and Geometry-Based Precise Point Positioning Models and Their Implication for Orbit and Clock Quality

Chen

Liu

Zhao

2018

Sensors

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Orbit and clock products are used in real-time global navigation satellite systems (GNSS) precise point positioning (PPP) without knowing their quality. This study develops a new approach to detect orbit and clock errors through comparing geometry-free and geometry-based wide-lane ambiguities in a PPP model. The reparameterization and estimation procedures of the geometry-free and geometry-based ambiguities are described in detail. The effects of orbit and clock errors on ambiguities are given in analytical expressions. The numerical similarity and differences of geometry-free and geometry-based wide-lane ambiguities are analyzed using different orbit and clock products. Furthermore, two types of typical errors in orbit and clock are simulated and their effects on wide-lane ambiguities are numerically produced and analyzed. The contribution discloses that the geometry-free and geometry-based wide-lane ambiguities are equivalent in terms of their formal errors. Although they are very close in terms of their estimates when the used orbit and clock for geometry-based ambiguities are precise enough, they are not the same, in particular, in the case that the used orbit and clock, as a combination, contain significant errors. It is discovered that the discrepancies of geometry-free and geometry-based wide-lane ambiguities coincide with the actual time-variant errors in the used orbit and clock at the line-of-sight direction. This provides a quality index for real-time users to detect the errors in real-time orbit and clock products, which potentially improves the accuracy of positioning.

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Real-Time PPP Based on the Coupling Estimation of Clock Bias and Orbit Error with Broadcast Ephemeris

Cited by 10 publications

References 14 publications

Tropospheric Delay Correction of VLBI Stations for the Real‐Time Trajectory Determination of the Chang'E‐5 Spacecraft

Tropospheric Delay Correction of VLBI Stations for the Real‐Time Trajectory Determination of the Chang'E‐5 Spacecraft

An Improved QZSS Satellite Clock Offsets Prediction Based on the Extreme Learning Machine Method

Analysis of Wide-Lane Ambiguities Derived from Geometry-Free and Geometry-Based Precise Point Positioning Models and Their Implication for Orbit and Clock Quality

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