Influence of Precise Products on the Day-Boundary Discontinuities in GNSS Carrier Phase Time Transfer

Global navigation satellite system (GNSS) precise point positioning (PPP) has been widely used for high-precision time and frequency transfer. However, the day-boundary discontinuities at the boundary epochs of adjacent days or batches are the most significant obstacle preventing PPP from continuous time transfer. The day-boundary discontinuities in station estimates and time comparisons are mainly caused by the code-pseudorange noise during the analysis of observation data in daily batches, where the absolute clock offset is determined by the average code measurements. However, some discontinuities with amplitudes even more than 0.15 ns may still appear in station clock estimates and time comparisons, although several methods had been proposed to remove such discontinuities. The residual small amplitude of the day-boundary discontinuities in some PPP station clock estimates and time comparisons through new GNSSs like Galileo seems larger, especially using precise clock products with large discontinuities. To further understand the origin of the day-boundary discontinuities, the influence of GNSS precise products on the day-boundary discontinuities in PPP station clock estimates and time comparisons is investigated in this paper. Ten whole days of Multi-GNSS Experiment (MGEX) from modified Julian date (MJD) 59028 to 59037 are used as the observation data. For a comparative analysis, the station clock estimates are compared with global positioning system (GPS) and Galileo observations through PPP and network solutions, separately. The experimental results show that the daily discontinuities in current combined GPS final and rapid clock products are less than 0.1 ns, and their influence on the origin of day-boundary discontinuities in PPP station clock estimates and time comparison are statistically negligible. However, the daily discontinuities in individual Analysis Centers (ACs) GPS products are more extensive, and their influence on the origin of the day-boundary discontinuities in GPS PPP station clock estimates cannot be ignored. The day-boundary discontinuities demonstrate random walk noise characteristics and deteriorate the station clocks’ long-term frequency stability, especially at an average time of more than one day. Although Galileo clock daily discontinuities are different from those of GPS, their influence on the day-boundary discontinuities in station clock estimates is nearly similar to the GPS PPP. The influence of daily discontinuities of Galileo clocks on PPP time comparison is similar to GPS and is not particularly critical to time comparison. However, combined and weighted MGEX products should be developed or Galileo IPPP should be used for remote comparison of high-stability clocks.

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Consideration of GLONASS Inter-Frequency Code Biases in Precise Point Positioning (PPP) International Time Transfer

Applied Sciences ◽

10.3390/app8081254 ◽

2018 ◽

Vol 8 (8) ◽

pp. 1254 ◽

Cited By ~ 9

Author(s):

Yulong Ge ◽

WeiJin Qin ◽

Xinyun Cao ◽

Feng Zhou ◽

Shengli Wang ◽

...

Keyword(s):

Precise Point Positioning ◽

Satellite Observation ◽

Satellite System ◽

Observation Data ◽

Time Transfer ◽

International Gnss Service ◽

Frequency Code ◽

Glonass Satellite ◽

Point Positioning ◽

Global Navigation Satellite

International time transfer based on Global Navigation Satellite System (GLONASS) precise point positioning (PPP) is influenced by inter-frequency code biases (IFCBs) because of the application of frequency division multiple access technique. This work seeks to gain insight into the influence of GLONASS IFCBs on international time transfer based on GLONASS-only PPP. With a re-parameterization process, three IFCB handling schemes are proposed: neglecting IFCBs, estimating IFCB for each GLONASS frequency number, and estimating IFCB for each GLONASS satellite. Observation data collected from 39 globally distributed stations in a 71-day period (DOY 227–297, 2017) was exclusively processed. For the comparison reason, Global Positioning System (GPS)-only PPP solutions were regarded as reference values. The clock differences derived from GPS- and GLONASS-only PPP solutions were then analyzed. The experimental results demonstrated that considering GLONASS IFCBs could reduce standard deviation (STD) of the clock differences for both identical receiver types and mixed receiver types, of which reduction was from 3.3% to 62.6%. Furthermore, compared with neglecting IFCBs, STD of the clock differences with estimating IFCB for each GLONASS satellite in coordinate-fixed mode was reduced by more than 30% from 0.30 to 0.20 ns, and by 10% from 0.40 to 0.35 ns, for 1-day arc solutions and 10-day arc solutions, respectively. Moreover, different precise products from three International GNSS Service (IGS) analysis centers were also evaluated. Even though different IFCB handling schemes were adopted in GLONASS satellite clock estimation, our numerical results showed that international time transfer on the basis of estimating IFCB for each GLONASS satellite better than the other two processing schemes. To achieve high-precision GLONASS-only PPP-based international time transfer, it is highly recommended to estimate IFCB for each GLONASS satellite.

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Online Near real-time Mine Disaster Monitoring System Based on Geosensor Networks

International Journal of Online Engineering (iJOE) ◽

10.3991/ijoe.v12i03.5450 ◽

2016 ◽

Vol 12 (03) ◽

pp. 64

Author(s):

Haifeng Hu

Keyword(s):

Real Time ◽

Monitoring System ◽

Satellite System ◽

Open Pit ◽

Observation Data ◽

Complex Data ◽

Disaster Monitoring ◽

Process Observation ◽

Global Navigation Satellite ◽

Safety And Stability

Abstract—An online automatic disaster monitoring system can reduce or prevent geological mine disasters to protect life and property. Global Navigation Satellite System receivers and the GeoRobot are two kinds of in-situ geosensors widely used for monitoring ground movements near mines. A combined monitoring solution is presented that integrates the advantages of both. In addition, a geosensor network system to be used for geological mine disaster monitoring is described. A complete online automatic mine disaster monitoring system including data transmission, data management, and complex data analysis is outlined. This paper proposes a novel overall architecture for mine disaster monitoring. This architecture can seamlessly integrate sensors for long-term, remote, and near real-time monitoring. In the architecture, three layers are used to collect, manage and process observation data. To demonstrate the applicability of the method, a system encompassing this architecture has been deployed to monitor the safety and stability of a slope at an open-pit mine in Inner Mongolia.

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A Joint Dual-Frequency GNSS/SINS Deep-Coupled Navigation System for Polar Navigation

Applied Sciences ◽

10.3390/app8112322 ◽

2018 ◽

Vol 8 (11) ◽

pp. 2322 ◽

Cited By ~ 2

Author(s):

Lin Zhao ◽

Mouyan Wu ◽

Jicheng Ding ◽

Yingyao Kang

Keyword(s):

Navigation System ◽

Density Ratio ◽

Satellite System ◽

The Arctic ◽

Observation Data ◽

Dual Frequency ◽

Vector Tracking ◽

Time Observation ◽

Global Navigation Satellite ◽

Navigation Accuracy

The strategic position of the polar area and its rich natural resources are becoming increasingly important, while the northeast and northwest passages through the Arctic are receiving much attention as glaciers continue to melt. The global navigation satellite system (GNSS) can provide real-time observation data for the polar areas, but may suffer low elevation problems of satellites, signals with poor carrier-power-to-noise-density ratio (C/N0), ionospheric scintillations, and dynamic requirements. In order to improve the navigation performance in polar areas, a deep-coupled navigation system with dual-frequency GNSS and a grid strapdown inertial navigation system (SINS) is proposed in the paper. The coverage and visibility of the GNSS constellation in polar areas are briefly reviewed firstly. Then, the joint dual-frequency vector tracking architecture of GNSS is designed with the aid of grid SINS information, which can optimize the tracking band, sharing tracking information to aid weak signal channels with strong signal channels and meet the dynamic requirement to improve the accuracy and robustness of the system. Besides this, the ionosphere-free combination of global positioning system (GPS) L1 C/A and L2 signals is used in the proposed system to further reduce ionospheric influence. Finally, the performance of the system is tested using a hardware simulator and semiphysical experiments. Experimental results indicate that the proposed system can obtain a better navigation accuracy and robust performance in polar areas.

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Improved Ultra-Rapid UT1-UTC Determination and Its Preliminary Impact on GNSS Satellite Ultra-Rapid Orbit Determination

Remote Sensing ◽

10.3390/rs12213584 ◽

2020 ◽

Vol 12 (21) ◽

pp. 3584

Author(s):

Fei Ye ◽

Yunbin Yuan ◽

Zhiguo Deng

Keyword(s):

Piecewise Linear ◽

Satellite System ◽

Assessment System ◽

Least Square ◽

Linear Functions ◽

Observation Data ◽

Combination Model ◽

New Strategy ◽

Global Navigation Satellite ◽

Traditional Strategy

Errors in ultra-rapid UT1-UTC primarily affect the overall rotation of spatial datum expressed by GNSS (Global Navigation Satellite System) satellite ultra-rapid orbit. In terms of existing errors of traditional strategy, e.g., piecewise linear functions, for ultra-rapid UT1-UTC determination, and the requirement to improve the accuracy and consistency of ultra-rapid UT1-UTC, the potential to improve the performance of ultra-rapid UT1-UTC determination based on an LS (Least Square) + AR (Autoregressive) combination model is explored. In this contribution, based on the LS+AR combination model and by making joint post-processing/rapid UT1-UTC observation data, we propose a new strategy for ultra-rapid UT1-UTC determination. The performance of the new strategy is subsequently evaluated using data provided by IGS (International GNSS Services), iGMAS (international GNSS Monitoring and Assessment System), and IERS (International Earth Rotation and Reference Systems Service). Compared to the traditional strategy, the numerical results over more than 1 month show that the new strategy improved ultra-rapid UT1-UTC determination by 29–43%. The new strategy can provide a reference for GNSS data processing to improve the performance of ultra-rapid products.

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Autonomous Navigation of a Mobile Robot Based on GNSS/DR Integration in Outdoor Environments

Journal of Robotics and Mechatronics ◽

10.20965/jrm.2014.p0214 ◽

2014 ◽

Vol 26 (2) ◽

pp. 214-224 ◽

Cited By ~ 13

Author(s):

Taro Suzuki ◽

◽

Mitsunori Kitamura ◽

Yoshiharu Amano ◽

Nobuaki Kubo ◽

...

Keyword(s):

Mobile Robot ◽

Autonomous Navigation ◽

Dead Reckoning ◽

Satellite System ◽

Mobile Robot Navigation ◽

Observation Data ◽

Multipath Mitigation ◽

Ir Camera ◽

Outdoor Environments ◽

Global Navigation Satellite

This paper describes the development of a mobile robot system and an outdoor navigationmethod based on global navigation satellite system (GNSS) in an autonomous mobile robot navigation challenge, called the Tsukuba Challenge, held in Tsukuba, Japan, in 2011 and 2012. The Tsukuba Challenge promotes practical technologies for autonomous mobile robots working in ordinary pedestrian environments. Many teams taking part in the Tsukuba Challenge used laser scanners to determine robot positions. GNSS was not used in localization because its positioning has multipath errors and problems in availability. We propose a technique for realizing multipath mitigation that uses an omnidirectional IR camera to exclude “invisible” satellites, i.e., those entirely obstructed by a building and whose direct waves therefore are not received. We applied GPS / dead reckoning (DR) integrated based on observation data from visible satellites determined by the IR camera. Positioning was evaluated during Tsukuba Challenge 2011 and 2012. Our robot ran the 1.4 km course autonomously and evaluation results confirmed the effectiveness of our proposed technique and the feasibility of its highly accurate positioning.

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A Method to Improve the Distribution of Observations in GNSS Water Vapor Tomography

Sensors ◽

10.3390/s18082526 ◽

2018 ◽

Vol 18 (8) ◽

pp. 2526 ◽

Cited By ~ 8

Author(s):

Fei Yang ◽

Jiming Guo ◽

Junbo Shi ◽

Lv Zhou ◽

Yi Xu ◽

...

Keyword(s):

Water Vapor ◽

Precipitable Water ◽

Absolute Error ◽

Satellite System ◽

Observation Data ◽

Radiosonde Station ◽

Satellite Signal ◽

Comparative Results ◽

Global Navigation Satellite ◽

Vapor Distribution

Water vapor is an important driving factor in the related weather processes in the troposphere, and its temporal-spatial distribution and change are crucial to the formation of cloud and rainfall. Global Navigation Satellite System (GNSS) water vapor tomography, which can reconstruct the water vapor distribution using GNSS observation data, plays an increasingly important role in GNSS meteorology. In this paper, a method to improve the distribution of observations in GNSS water vapor tomography is proposed to overcome the problem of the relatively concentrated distribution of observations, enable satellite signal rays to penetrate more tomographic voxels, and improve the issue of overabundance of zero elements in a tomographic matrix. Numerical results indicate that the accuracy of the water vapor tomography is improved by the proposed method when the slant water vapor calculated by GAMIT is used as a reference. Comparative results of precipitable water vapor (PWV) and water vapor density (WVD) profiles from radiosonde station data indicate that the proposed method is superior to the conventional method in terms of the mean absolute error (MAE), standard deviations (STD), and root-mean-square error (RMS). Further discussion shows that the ill-condition of tomographic equation and the richness of data in the tomographic model need to be discussed separately.

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Comparison of Multi-GNSS Time and Frequency Transfer Performance Using Overlap-Frequency Observations

Remote Sensing ◽

10.3390/rs13163130 ◽

2021 ◽

Vol 13 (16) ◽

pp. 3130

Author(s):

Pengfei Zhang ◽

Rui Tu ◽

Yuping Gao ◽

Ju Hong ◽

Junqiang Han ◽

...

Keyword(s):

Carrier Phase ◽

Satellite System ◽

Single Frequency ◽

Navigation Satellite ◽

Transfer Performance ◽

Dual Frequency ◽

Time Transfer ◽

Difference Series ◽

Frequency Transfer ◽

Global Navigation Satellite

The modernized GPS, Galileo, and BeiDou global navigation satellite system (BDS3) offers new potential for time transfer using overlap-frequency (L1/E1/B1, L5/E5a/B2a) observations. To assess the performance of time and frequency transfer with overlap-frequency observations for GPS, Galileo, and BDS3, the mathematical models of single- and dual-frequency using the carrier-phase (CP) technique are discussed and presented. For the single-frequency CP model, the three-day average RMS values of the L5/E5a/B2a clock difference series were 0.218 ns for Galileo and 0.263 ns for BDS3, of which the improvements were 36.2% for Galileo and 43.9% for BDS3 when compared with the L1/E1/B1 solution at BRUX–PTBB. For the hydrogen–cesium time link BRUX–KIRU, the RMS values of the L5/E5a/B2a solution were 0.490 ns for Galileo and 0.608 ns for BDS3, improving Galileo by 6.4% and BDS3 by 12.5% when compared with the L1/E1/B1 solution. For the dual-frequency CP model, the average stability values of the L5/E5a/B2a solution at the BRUX–PTBB time link were 3.54∙× 10−12 for GPS, 2.20 × 10−12 for Galileo, and 2.69 × 10−12 for BDS3, of which the improvements were 21.0%, 45.1%, and 52.3%, respectively, when compared with the L1/E1/B1 solution. For the BRUX–KIRU time link, the improvements were 4.2%, 30.5%, and 36.1%, respectively.

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Investigation of Unmanned Aerial Vehicles-Based Photogrammetry for Large Mine Subsidence Monitoring

Minerals ◽

10.3390/min10020196 ◽

2020 ◽

Vol 10 (2) ◽

pp. 196 ◽

Cited By ~ 1

Author(s):

Danijela Ignjatović Stupar ◽

Janez Rošer ◽

Milivoj Vulić

Keyword(s):

Unmanned Aerial Vehicles ◽

Coal Mine ◽

Negative Impact ◽

Local Environment ◽

Satellite System ◽

Reference Points ◽

Coal Extraction ◽

Observation Data ◽

Aerial Vehicles ◽

Global Navigation Satellite

With the exploitation of underground sources, nature receives a huge negative impact on the local environment introducing surface subsidence. A mining region needs to be observed in sequences before, during, and after coal extraction from the coal mine. Different measuring methods exist to monitor subsidence, and all of them apply various instrumentation. A choice of methodology depends on access to a field of observation and requested accuracy. Obviously, the most accurate results provide geometric leveling, but, many times, the terrain does not allow surveyors to walk over the dangerous outfields. Looking for the most adequate and feasible method, this research did a comparison between observation of the same points, applying statistical analysis of differences between the reference points heights, and tested methods. Monitoring procedure comprised utilization of total stations (TS), global navigation satellite system (GNSS), and unmanned aerial vehicles (UAV). In this paper, the Velenje coal mine was taken as a case study, and observation data were collected during 2017.

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The effect of the GNSS time transfer performance for geopotential difference determination

10.5194/egusphere-egu21-1895 ◽

2021 ◽

Author(s):

Chenghui Cai ◽

Wen-Bin Shen ◽

Ziyu Shen ◽

Wei Xu ◽

Lei Wang

Keyword(s):

Natural Science ◽

Space Station ◽

Satellite System ◽

Relativity Theory ◽

Time Transfer ◽

Simulation Experiments ◽

Good Opportunity ◽

Free Running ◽

Global Navigation Satellite ◽

The Relationship

<p>The quick development of the global navigation satellite system (GNSS) time transfer technique provides a good opportunity to determine the geopotential difference based on the general relativity theory (GRT). In this study, we propose an approach that uses the precise point positioning (PPP) technique to directly compute clock offsets between two clocks at two arbitrary positions for the purpose of determining the geopotential difference and the accuracy of this approach depends not only on both the accuracies and stabilities of clocks, but also the time transfer technique itself. To validate the relationship between the performance of GNSS time transfer and the accuracy of this approach, simulation experiments are conducted.<strong> </strong>We evaluated the performances of GNSS time transfer in different cases using different type of free-running clocks, and results show that the proposed approach could be applied to testing GRT. This study was supported by the National Natural Science Foundations of China (grant Nos. 41721003, 42030105, 41804012, 41631072, 41874023, 41574007), Natural Science Foundation of Hubei Province of China (grant Nos. 2019CFB611), and Space Station Project (2020)228.</p>

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Study on GNSS Time Reference System and its Traceability

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.263-266.2031 ◽

2012 ◽

Vol 263-266 ◽

pp. 2031-2034

Author(s):

Shao Wu Dong

Keyword(s):

Global Navigation Satellite System ◽

Satellite System ◽

Time Measurement ◽

Universal Time ◽

Navigation Satellite ◽

Reference Systems ◽

Internal Time ◽

Precision Time ◽

Global Navigation Satellite ◽

Time Standard

This paper introduces briefly international standard time scale---theCoordinated Universal Time (UTC) and its realization, the time references and their traceability of Global Navigation Satellite System (GNSS). GNSS is based on precision time measurement, an uniform internal time reference is necessary to ensure all parts in a GNSS run synchronously. All GNSS system have precision time reference systems, at the same time, it is necessary that the time reference should be traced to the international legal time standard, UTC, to ensure global time synchronous and uniform, it can be realized by establishing time comparison link with national time standard. A possible solution of GNSS time reference and its traceability for COMPASS is discussed.

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