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Journal of Global Positioning Systems Vol. 17, No. 1, 2021 |
Cover |
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Journal of Global Positioning Systems
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JGPS Team Structure, Copyright and Table of Contents |
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JGPS Team Structure, Copyright
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1. A Resilient Smartphone Positioning Approach by Tightly Integrating the Monocular Camera and GNSS Signals |
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Han Xu, Lei Wang, Ruizhi Chen, Haitao Zhou, Tao Li and Yi Han
The Global Navigation Satellite System (GNSS) signals are often blocked or interfered in complex geographical or electromagnetic environments, which may make GNSS receivers unable to provide satisfying navigation and positioning services. There have been many ground-based or space-based GNSS augmentation systems to improve the resilience of GNSS positioning, of which most of them rely on additional infrastructures. In this study, a smartphone-based tightly-coupled positioning method was developed using the images from a build-in monocular camera and GNSS signals. In this method, the feature points with the known coordinates are regarded as 'visual pseudolite' and the distance between the camera and the feature points was calculated according to the photogrammetry approaches and used to estimate the user positioning with GNSS signals. The experimental results showed the feasibility of the tightly-coupled positioning algorithm and reached the positioning accuracy of ±5.56 m (1σ), which is significantly higher than that of GNSS-only and vision-only positioning solutions.
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2. Improvement of Integrated Water Vapor Products from Sentinel-3 OLCI NIR Channels Using Ground-based GPS Measurements |
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Jiafei Xu and Zhizhao Liu
High-quality remote sensing water vapor monitoring plays a vital role in Earth's weather and climate observation. In this work, we developed a model to improve the accuracy of integrated water vapor (IWV) products retrieved from the Ocean and Land Color Instrument (OLCI) near-infrared (NIR) channels using ground-based GPS-derived IWV data. This algorithm uses the empirical regression equations to calibrate the official OLCI IWV products published by Sentinel-3. The reference IWV data, from June 1, 2018 to May 31, 2019, from 453 GPS sites over Australia, were employed to calculate the differential IWV data by subtracting GPS IWV data from OLCI IWV data. The OLCI IWV pixels were grouped into two categories according to the quality flag of each pixel. For each group, the relationship between the differential IWV data and the official OLCI IWV products was defined, and the model parameters were independently calculated from each season. The performance of the model was evaluated using reference IWV data from GPS and European Centre for Medium-Range Weather Forecasts (ECMWF) from June 1, 2019 to May 31, 2020 over Australia. Taking GPS IWV data as reference, the root-mean-square error (RMSE) has reduced 27.63% from 3.475 to 2.515 mm for Sentinel-3A, and 18.06% from 4.030 to 3.302 mm for Sentinel-3B. Taking ECMWF IWV data as reference, the RMSE was reduced by 25.27% from 3.490 to 2.608 mm for Sentinel-3A, and by 23.54% from 3.535 to 2.703 mm for Sentinel-3B. The improvement of OLCI IWV products was further confirmed in Mainland China, with smaller RMSE against reference IWV data from 214 GPS stations from June 1, 2019 to May 31, 2020.
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3. BDS Real-time Satellite Clock Offsets Estimation with Three Different Datum Constraints |
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Guanwen Huang, Wei Xie, Wenju Fu, Pingli Li, Haohao Wang and Fan Yue
A clock offset datum should be selected to separate the satellite and receiver clock offset when estimating the Global Navigation Satellite System (GNSS) satellite clock offset. However, the applicable conditions and performance of the estimated satellite clock offset vary for different clock offset datums. In this paper, the BeiDou Navigation Satellite System (BDS) real-time satellite clock offset is estimated by using the undifferenced (UD) model with three datum constraints: receiver clock datum, satellite clock datum, and zero-mean condition (ZMC) datum. The constraint conditions of three clock offset datums are discussed, the transformation relationship among the three datums constraints is derived, and the characteristics of three clock offset datums are analyzed. One hundred stations were used to perform the experiments, and the results show mean standard deviation (STD) values of 0.118, 0.124, and 0.101 ns for the receiver clock, satellite clock, and ZMC datum, respectively. The mean clock offset model precisions with the three datum are 0.497, 0.646, and 0.442 ns, respectively. The frequency stability with ZMC datum results showed the best performance when the integration time is less than 10,000 s. For precise point positioning (PPP), the ZMC datum results show better performance among the three datum constraints. This study can provide a reference for clock offset datum selection for GNSS satellite clock offset estimation.
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4. Performance assessment of the generalized DIA estimators applied in GNSS positioning |
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Ling Yang
This paper discusses the performance assessment of the generalized DIA estimators. Based on the unifying framework of the DIA estimators introduced by Teuniseen (2018), quality control indices from three aspects are discussed and formulated, to measure the confidence levels of the testing decisions, to evaluate the reliability of the specified alternative hypothesis models, as well as to compute the biasedness, dispersion and integrity of the estimated parameters under an unconditional case, by taking the uncertainty of the combined estimation-testing procedure into account and performing the propagation of uncertainty accordingly. With a dual-constellation GNSS single-point positioning example, the quality control evaluation of and comparisons among three conventional used DIA estimators are demonstrated for practical applications.
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5. Performance Analysis of BDS-2, BDS-3 and GPS in Relative Positioning through Short, Medium and Long Baselines |
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Huizhong Zhu, Jingfa Zhang, Jun Li, Qi Xu, YangYang Lu and Aigong Xu
BDS-3 (Beidou System 3) reached global coverage in June 2020. In comparison with BDS-2 (Beidou system 2), BDS-3 has greatly improved in terms of satellite orbits, atomic clocks and signal transmissions. BDS-3 is now being used widely in practice. This paper is focused on performance analysis of BDS-3 vs.BDS-2 and GPS. Six baselines of different lengths were selected to result in single-system multi-frequency relative positioning solutions from BDS-2, BDS-3 and GPS, respectively. The long baselines were resolved by using the random walk constraints on the residual atmospheric delay. The positioning performance of each system was analysed against the atmospheric delay error and the convergence property of the floated ambiguity resolution. The experiments showed that the convergence speed of BDS-3 was twice as fast as BDS-2, and the average convergence speed was also faster than GPS, which was increased by about 2.7%. In comparison with BDS-2, the accuracy of BDS-3 was improved by about 40%, but the accuracy was 7% lower than the GPS solution and the positioning stability of BDS-3 was also not as good as GPS.
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6. Fault detection of integrated navigation system based on genetic algorithm optimization for deep belief network |
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Weiyu Kong, Ya Zhang and Jiachong Chang
An accurate fault detection method is critical in preventing the integrity of integrated navigation system from the abnormal measurements which may occur any time. Here, a genetic algorithm optimization for deep belief network fault detection method is proposed, where the system measuring residuals sequence is used as the input, and the output is the system operating state, such as normal or fault types, in pointwise. The proposed technique extracts the features with various scales, which contain both the local and the general information of the signal sequence, for making a comprehensive and precise classification. To show the validity of the proposed method, simulations based on INS/GNSS integrated navigation system are carried out. The simulation results show that the proposed fault detection algorithm and method is superior to the existing algorithms on the faults detection rate and false alarm rate, and thus, system reliability and navigation precision have been greatly improved.
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ABSTRACTS OF PHD DISSERTATIONS |
1. Research on the Key Technologies in Water Vapor Retrieval Using Ground-based GNSS |
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Yang Fei
As the most abundant greenhouse gas in the earth
atmosphere, water vapor plays an important role in
maintaining livable temperature environment and
contributes much to the global warming. The content
of water vapor in the atmosphere is pretty variable in
both temporal and spatial domain, which greatly
affects the climate and weather system. The phase
change of water vapor is accompanied by the
absorption and release of heat, which has a significant
influence on the vertical stability of the atmosphere
and the formation of the severe convection weather.
Its dramatic change in a short time always leads to
destructive weathers. Therefore, monitoring the
content and distribution of water vapor in the
atmosphere and a good understanding of the spatial
and temporal change of water vapor are of great
significance to the research of climate change, the
short-term weather forecasts, and the severe weather
warning.
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2. Research on Pedestrian Indoor Multi-Source Positioning Algorithm Based on Strapdown PDR and Magnetic Field Matching for Smartphone |
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Jian Kuang
To meet the needs of consumers for
outdoor/indoor seamless location-based services
(LBS), there is an urgent need for indoor positioning
technologies. This thesis proposes an indoor
multi-source positioning solution based on the
smartphone built-in sensors, environmental magnetic
field distortion feature, and Bluetooth Low Energy
(BLE) fingerprint. The highlights of the thesis are 1)
enhancing the autonomous recursive positioning
ability of pedestrian dead reckoning (PDR) by using
strapdown inertial algorithm that is fully
self-contained; 2) using the relative trajectory pattern
generated by PDR to improve the accuracy of
magnetic field feature matching and BLE fingerprint
matching, to ultimately improving the performance of
the multi-source integrated positioning.
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3. Ground-based GNSS Remote Sensing for Near-surface Water Environmental Parameters |
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Xiaolei Wang
The expansion of research and application of the
global navigation satellite systems (GNSS) has
revealed more information. Tropospheric delay caused
by atmospheric refraction and multipath error caused
by reflected signals were thought to be two important
errors in GNSS positioning. However, these refracted
and reflected signals carry characteristic information
of medium: the reflected signals can carry
characteristic information of the reflecting surface
(including sea level, snow depth, soil moisture, et al.);
and the refracted signals can carry information of the
atmospheric water vapor. Based on this information,
some water environmental parameters such as water
vapor, soil moisture, snow depth and sea level can be
retrieved based on two ground-based GNSS remote
sensing technologies - GNSS-Interferometry
Reflectometry (GNSS-IR) and GNSS Precipitable
Water Vapor (GNSS-PWV).
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Back Cover |
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Journal of Global Positioning Systems
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