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Jiexian Wang

Bio: Jiexian Wang is an academic researcher from Tongji University. The author has contributed to research in topics: GNSS applications & Global Positioning System. The author has an hindex of 10, co-authored 40 publications receiving 314 citations. Previous affiliations of Jiexian Wang include State Bureau of Surveying and Mapping.

Papers
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Journal ArticleDOI
TL;DR: A simplified and unified model for multi-GNSS PPP is developed, where ISB parameter does not need to be estimated and observations from different GNSS systems are treated in a unified way.

54 citations

Journal ArticleDOI
TL;DR: In this article, the GPS measurements of five campaigns, which were carried out in Shanghai City from 2002 to 2005, are used to determine the velocity of each GPS monument, and the horizontal strain rate tensors are calculated with the relative velocities of the sites obtained.
Abstract: By applying integrated least-squares adjustment of multicampaigns geographic positioning system (GPS) measurements, the velocity of any GPS monument can be obtained. The resulting velocities are used to estimate the strain rate tensors and their variances under infinitesimal strain assumption in a discrete triangle. In this paper, the GPS measurements of five campaigns, which were carried out in Shanghai City from 2002 to 2005, are used to determine the velocity of each GPS monument. Then the horizontal strain rate tensors are calculated with the relative velocities of the sites obtained. The analysis of these principal strain rates together with a comparison of the geological information is performed. The patterns of the principal strain rates show a significant northwest to southeast extension zone in the southwestern part of Shanghai, which agrees well with the neo-tectonic activity of an existing geological fault, the so-called “Dachang–Zhoupu” fault.

39 citations

Journal ArticleDOI
TL;DR: In this paper, a method to assess the performance of the third-generation BeiDou navigation satellite system (BDS-3), in terms of satellite visibility and dilution of precision (DOP), on global and regional scales is presented.
Abstract: We describe a method to assess the performance of the third-generation BeiDou navigation satellite system (BDS-3), in terms of satellite visibility and dilution of precision (DOP), on global and regional scales. Different from traditional methods, this method estimates the satellite visibility and DOP without requiring real or simulated ephemerides. Validated by the reference values derived from real ephemerides of GPS and GLONASS, the estimated number of visible satellites achieves an accuracy better than 0.15, and the estimated DOP values are lower than their reference values by less than 10% on average. Applying this method to BDS-3, with a 5° cutoff elevation angle, results show that the geostationary earth orbit (GEO) and inclined geosynchronous orbit (IGSO) satellites of BDS-3 together contribute 3–6 visible satellites in the area of 60°S–60°N and 50°E–170°E. In this area, the number of visible BDS-3 satellites is 11–14, which is more than GPS and Galileo by 1–3, and GLONASS by 3–7. With better satellite visibility, the average BDS-3 horizontal, vertical, and time DOPs over this area are 0.74, 1.08, and 0.67, which are, respectively, 5%, 9%, and 3% lower than those of GPS and Galileo, 14%, 16%, and 21% lower than those of GLONASS, and 16%, 19% and 14% lower than those of the 24-MEO-only BDS-3.

38 citations

Journal ArticleDOI
TL;DR: This paper comprehensively assess the system status and the global positioning performance of BDS regarding single point positioning (SPP) and real-time kinematic (RTK) performance and shows that the signal in space range error (SISRE) of BDS-3 satellites is superior to that of BDS -2 satellites.
Abstract: With the official announcement of open service since the end of 2018, the BeiDou navigation satellite system (BDS) has started to provide global positioning, navigation and timing (PNT) services. Thus, it is worth assessing the positioning service of new BDS satellites and signals. In this paper, we comprehensively assess the system status and the global positioning performance of BDS regarding single point positioning (SPP) and real-time kinematic (RTK) performance. Results show that the signal in space range error (SISRE) of BDS-3 satellites is superior to that of BDS-2 satellites, showing an overall accuracy of 0.71 m versus 0.97 m, which is competitive with GPS and Galileo. With the contribution of BDS-3, the number of global average visible satellites has increased from 5.1 to 10.7, which provides a mean global position dilution of precision (PDOP) value better than 6 at 99.88% and the mean availability of basic PNT performance is also improved from 35.25% to 98.84%. One week of statistical results from 54 globally distributed international GNSS service (IGS) stations show that the root mean square (RMS) of SPP accuracy is 1.1 m in horizontal and 2.2 m in vertical, which is at the same level of GPS. The new B1c and B2a signals show a smaller observation noise than B1I, and SPP performance of B1c is similar to that of B1I. However, the positioning precision is slightly worse at the B2a frequency, which may be due to the inaccurate BDS ionosphere correction. As for short baseline RTK, baseline accuracy is also improved due to the increased number of new BDS satellites.

38 citations

Journal ArticleDOI
TL;DR: Results show that the IFCBs of PRN25 and PRN01 exhibit periodical signal of one orbit revolution with a magnitude up to 18 cm, which enables a consistent use of L1/L2 clock products in L 1/L5-based positioning.
Abstract: We present two efficient approaches, namely the epoch-differenced (ED) and satellite- and epoch-differenced (SDED) approaches, for the estimation of IFCBs of the two Block IIF satellites. For the analysis, data from 18 stations from the IGS network spanning 96 d is processed. Results show that the IFCBs of PRN25 and PRN01 exhibit periodical signal of one orbit revolution with a magnitude up to 18 cm. The periodical variation of the IFCBs is modeled by a sinusoidal function of the included angle between the sun, earth and the satellite. The presented model enables a consistent use of L1/L2 clock products in L1/L5-based positioning. The algorithm is incorporated into the MGPSS software at SHAO (Shanghai Astronomical Observatory, Chinese Academy of Sciences) and is used to monitor the IFCB variation in near real-time.

35 citations


Cited by
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01 Dec 2013
TL;DR: In this paper, the authors investigated the connection between annual maxima (AM) daily precipitation at a pan-European scale and atmospheric rivers (ARs), narrow filaments that convey the majority of the poleward water vapor transport within extratropical cyclones.
Abstract: [1] Extreme precipitation and floods in Europe are a recurring natural hazard causing large socioeconomic damages. Here we investigate the connection between annual maxima (AM) daily precipitation at a pan-European scale and atmospheric rivers (ARs), narrow filaments that convey the majority of the poleward water vapor transport within extratropical cyclones. We show that ARs are responsible for many AM precipitation days in Western Europe. The relationship is especially strong along the western European seaboard, with some areas having eight of their top 10 AM related to ARs. The effects of ARs are also seen as far inland as Germany and Poland. Southern Europe was most affected by ARs under negative North Atlantic Oscillation (NAO) conditions, whereas northern Europe was more associated with a positive relationship between ARs and an NAO-type pattern. Our results suggest that ARs are critical in explaining the upper tail of the extreme precipitation distribution in Western Europe.

228 citations

Journal ArticleDOI
TL;DR: A method of short-term prediction of RTS corrections that extends the application period of obsolete correction data without a significant loss in orbit quality is proposed and it is possible to forecast the orbit corrections reliably up to 8 min for GPS and 4 Min for GLONASS.
Abstract: The International GNSS Service (IGS) real-time service (RTS) provides access to real-time precise products such as orbits, clocks and code biases, which can be used as a substitute for ultra-rapid products in real-time applications. The true performance of these products can be assessed by the Analysis Centers daily statistics derived from the comparison with IGS rapid products. Additionally, indirect verification is performed by their application to various precise point positioning strategies. Monitoring results and basic descriptions of these products are available at the official RTS Web page ( http://rts.igs.org/ ). We present a more detailed description of RTS products. Information from various sources is collected to provide products application methodology and describe their important features. We provide extended verification of the products using 1 week of real-time correction data. Results are presented separately for GNSS constellations, considering satellite block and type of onboard clock. Comparison with ESA/European Space Operations Centre final products proves the high accuracy of RTS orbits and clocks, which is 5 cm for GPS orbits, 8 cm for GPS clocks, 13 cm for GLONASS orbits and 24 cm for GLONASS clocks. The real-time correction performance is also examined regarding availability and latency. In general, the availability of corrections was beyond 95 % for GPS and beyond 90 % for GLONASS. Since the increasing degradation of product quality with latency is critical for real-time applications, the relation between product latency and accuracy is analyzed. It confirms that high-rate stream update intervals are suitable for the data provided and that the obsolete data should not be used. To avoid this, we propose a method of short-term prediction of RTS corrections that extends the application period of obsolete correction data without a significant loss in orbit quality. Using polynomial fitting, it is possible to forecast the orbit corrections reliably up to 8 min for GPS and 4 min for GLONASS.

207 citations

Journal ArticleDOI
TL;DR: This study presents the results and the methodology for estimation and accounting for phase and code GPS-Galileo inter-system bias in precise relative positioning and examines the influence of accounting for the inter- system bias on the user position solution.
Abstract: Availability of two overlapping frequencies L1/E1 and L5/E5a of the signals transmitted by GPS and Galileo systems offers the possibility of tightly combining observations from both systems in a single observational model. A tightly combined observational model assumes a single reference satellite for all observations from both Galileo and GPS systems. However, when inter-system double-differenced observations are created, receiver inter-system bias is introduced. This study presents the results and the methodology for estimation and accounting for phase and code GPS-Galileo inter-system bias in precise relative positioning. The research investigates the size and temporal stability of the estimated bias for different receiver pairs as well as examines the influence of accounting for the inter-system bias on the user position solution. The obtained numerical results are based on four experiments carried out at different locations and time periods using both real and simulated GNSS data.

151 citations

Journal ArticleDOI
TL;DR: The results demonstrate that the observational quality of the new-generation BeiDou-3 signals is comparable to that of GPS L1/L2/L5 and Galileo E1/E 5a/E5b signals.
Abstract: The successful launch of five new-generation experimental satellites of the China’s BeiDou Navigation Satellite System, namely BeiDou I1-S, I2-S, M1-S, M2-S, and M3-S, marks a significant step in expanding BeiDou into a navigation system with global coverage. In addition to B1I (1561.098 MHz) and B3I (1269.520 MHz) signals, the new-generation BeiDou-3 experimental satellites are also capable of transmitting several new navigation signals in space, namely B1C at 1575.42 MHz, B2a at 1176.45 MHz, and B2b at 1207.14 MHz. For the first time, we present an initial characterization and performance assessment for these new-generation BeiDou-3 satellites and their signals. The L1/L2/L5 signals from GPS Block IIF satellites, E1/E5a/E5b signals from Galileo satellites, and B1I/B2I/B3I signals from BeiDou-2 satellites are also evaluated for comparison. The characteristics of the B1C, B1I, B2a, B2b, and B3I signals are evaluated in terms of observed carrier-to-noise density ratio, pseudorange multipath and noise, triple-frequency carrier-phase ionosphere-free and geometry-free combination, and double-differenced carrier-phase and code residuals. The results demonstrate that the observational quality of the new-generation BeiDou-3 signals is comparable to that of GPS L1/L2/L5 and Galileo E1/E5a/E5b signals. However, the analysis of code multipath shows that the elevation-dependent code biases, which have been previously identified to exist in the code observations of the BeiDou-2 satellites, seem to be not obvious for all the available signals of the new-generation BeiDou-3 satellites. This will significantly benefit precise applications that resolve wide-lane ambiguity based on Hatch–Melbourne–Wubbena linear combinations and other applications such as single-frequency precise point positioning (PPP) based on the ionosphere-free code–carrier combinations. Furthermore, with regard to the triple-frequency carrier-phase ionosphere-free and geometry-free combination, it is found that different from the BeiDou-2 and GPS Block IIF satellites, no apparent bias variations could be observed in all the new-generation BeiDou-3 experimental satellites, which shows a good consistency of the new-generation BeiDou-3 signals. The absence of such triple-frequency biases simplifies the potential processing of multi-frequency PPP using observations from the new-generation BeiDou-3 satellites. Finally, the precise relative positioning results indicate that the additional observations from the new-generation BeiDou-3 satellites can improve ambiguity resolution performance with respect to BeiDou-2 only positioning, which indicates that observations from the new-generation BeiDou-3 satellites can contribute to precise relative positioning.

150 citations

Journal ArticleDOI
TL;DR: A GPS + BDS fractional cycle bias (FCB) estimation method and a PPP AR model developed using integrated GPS and BDS observations that outperforms single-system PPPAR in terms of convergence time and position accuracy are verified.
Abstract: This paper focuses on the contribution of the global positioning system (GPS) and BeiDou navigation satellite system (BDS) observations to precise point positioning (PPP) ambiguity resolution (AR). A GPS + BDS fractional cycle bias (FCB) estimation method and a PPP AR model were developed using integrated GPS and BDS observations. For FCB estimation, the GPS + BDS combined PPP float solutions of the globally distributed IGS MGEX were first performed. When integrating GPS observations, the BDS ambiguities can be precisely estimated with less than four tracked BDS satellites. The FCBs of both GPS and BDS satellites can then be estimated from these precise ambiguities. For the GPS + BDS combined AR, one GPS and one BDS IGSO or MEO satellite were first chosen as the reference satellite for GPS and BDS, respectively, to form inner-system single-differenced ambiguities. The single-differenced GPS and BDS ambiguities were then fused by partial ambiguity resolution to increase the possibility of fixing a subset of decorrelated ambiguities with high confidence. To verify the correctness of the FCB estimation and the effectiveness of the GPS + BDS PPP AR, data recorded from about 75 IGS MGEX stations during the period of DOY 123-151 (May 3 to May 31) in 2015 were used for validation. Data were processed with three strategies: BDS-only AR, GPS-only AR and GPS + BDS AR. Numerous experimental results show that the time to first fix (TTFF) is longer than 6 h for the BDS AR in general and that the fixing rate is usually less than 35 % for both static and kinematic PPP. An average TTFF of 21.7 min and 33.6 min together with a fixing rate of 98.6 and 97.0 % in static and kinematic PPP, respectively, can be achieved for GPS-only ambiguity fixing. For the combined GPS + BDS AR, the average TTFF can be shortened to 16.9 min and 24.6 min and the fixing rate can be increased to 99.5 and 99.0 % in static and kinematic PPP, respectively. Results also show that GPS + BDS PPP AR outperforms single-system PPP AR in terms of convergence time and position accuracy.

99 citations