Table of Content

20 July 2020, Volume 49 Issue 7

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Geodesy and Navigation

Assessment method and analysis of broadcast coordinated universal time offset error

JIAO Wenhai, ZHANG Huijun, ZHU Lin, LI Xiaohui, ZHU Feng

2020, 49(7):  805-815.  doi:10.11947/j.AGCS.2020.20190352

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Coordinated universal time offset error(UTCOE) which is the error of broadcasted coordinated universal time offset(UTCO) has become one of the focuses that global navigation satellite system(GNSS) provider and its users are concerned in recent years. This paper studies UTCOE definition, proposes an indirect assessment method of UTCOE based on Coordinated Universal Time(UTC) kept by National Time Service Center( UTC(NTSC)) and circular T bulletin published by International Bureau of Measurement(BIPM).The validity of the method is verified by using direct assessment method of GPS UTCOE. Furthermore, uncertainty budget of the assessment method is also given. The UTCOE of BDS, GPS and GLONASS are assessed utilizing the monitoring data from the running GNSS system time offset monitoring system at NTSC. During the assessment cycle throughout 2018, the root mean square (RMS) of BDS UTCOE is 17.33 ns. The 95% statistical value of UTCOE of BDS, GPS and GLONASS are 35.47、2.08 and 8.64 ns, respectively. The results show that the UTCOE of BDS, GPS and GLONASS all meet their own standard performance specifications. The UTCOE assessment results of GPS are far superior to its performance commitment. GLONASS is the second. BDS UTCOE assessment results are critical and show obvious systematic error characteristic. So, the UTCOE of BDS has a large room for promotion.

Nonlinear equality constrained total least squares adjustment combined with orthogonal geometry information and its iterative algorithm

HU Chuan, FANG Xing, ZHAO Lidu

2020, 49(7):  816-823.  doi:10.11947/j.AGCS.2020.20190112

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For the problem of fitting the independent variables with error, orthogonal distance least squares and weighted total least squares two independent approaches can be employed to solve it. However, the weighted total least square is unlike orthogonal distance least squares. It does not taking into account the orthogonal geometry information, namely, the line segment consisted of observation point and fitted point is vertical to fitted object. Aimed to solve this problem, a nonlinear equality constrained total least squares adjustment model is proposed, in which total least squares is combined with orthogonal geometry information that has been transformed into a nonlinear equality constraints function with unknown corrected errors. After the function model and the nonlinear equality constraints function are linearized, the Lagrange multiplier method is introduced to derive the calculation formula for estimating parameter and assessing accuracy. Two iterative algorithms are given correspondingly. The suggested method and the designed algorithm are tested by the example of fitting a straight-line. The results show that, ①the proposed model and the iterative algorithm are feasible; ②compared with weighted least squares and weighted total least squares, the sum square of orthogonal distance from the measured point to the fitted line calculated by the new method is the smallest value; ③this orthogonal distance is equal to the distance from the measured point to the corrected point calculated by the suggested method, and the other two methods are not like this.

Unified ambiguity resolution method based on three PPP Models

DU Zhenqiang, CHAI Hongzhou, XIANG Minzhi, YIN Xiao, LIU Chunhe

2020, 49(7):  824-832.  doi:10.11947/j.AGCS.2020.20190467

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The integer characteristics of the ambiguity can be recovered after the correction of fractional cycle biases (FCB), which can significantly shorten the initialization time of precise point positioning (PPP).However, the ambiguity resolution model of the clientend needs to be consistent with serverend, which may introduce the problem that the client maybe unable to use different FCB products and increases the transmission pressure of the server link. A unified PPP ambiguity resolution method is proposed that based on three PPP models,i.e.,ionosphere-free combination model, uncombined model without prior ionosphere constraint and uncombined model with prior ionosphere constraint.Different clients can use the same FCB product to achieve fast ambiguity resolution.A globally distributed network consisting of 116 MGEX stations is used to generates three kinds of FCB products at the server end, and 50 additional stations are selected at the client end for verification.The experimental results show that the new method solves the problem of ambiguity resolution of PPP at client end when facing different FCB products. Comparable performance with the traditional method can be achieved with regards to in positioning accuracy, convergence time and success rate.

Multi-star linear regression retrieval model for monitoring soil moisture using GPS-IR

LIANG Yueji, REN Chao, HUANG Yibang, PAN Yalong, ZHANG Zhigang

2020, 49(7):  833-842.  doi:10.11947/j.AGCS.2020.20190095

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Global positioning system interferometric reflectometry (GPS-IR) is a new remote sensing technique that can be used to estimate near-surface soil moisture from signal-to-noise ratio (SNR) data recorded by a measurement receiver. Considering that there are few studies on the inversion of soil moisture by multi-satellite combination, a multi-star linear regression soil moisture inversion model is proposed. The experiment shows that: ①The multi-satellite combination inversion mode can more comprehensively reflect the soil moisture information within the effective monitoring range near the station, and effectively improve the phenomenon that the inversion process is prone to abnormal jump when using single satellite inversion. At the same time, it improves the accuracy of soil moisture inversion during sudden rainfall periods. ②When the number of combined satellites reaches 6 or more, the correlation coefficient between the inversion result and the soil moisture reference value is greater than 0.9, which is at least 20.8% higher than that of a single satellite.

Ionospheric tomography method by reducing grid resolution locally

WANG Wenyue, YU Jieqing, WANG Ying, JIA Chenyi, WU Lixin, ZHANG Shaoliang

2020, 49(7):  843-853.  doi:10.11947/j.AGCS.2020.20190227

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The construction of the voxel model is an important part of computer ionospheric tomography (CIT) method. It will no doubt affect the accuracy of the CIT method. However, most existing researches focus on how to improve the image’s accuracy via inversion algorithm and few of them are concerned with the grid construction solution. This paper intends to improve accuracy by making some optimization on the voxel model. Some preliminary experiments were first carried out to explore the relationship between the accuracy of the image and its corresponding resolution. Then, based on the findings, a new CIT method, which is to improve the accuracy of the tomographic image of the interesting area at the price of reducing the resolution of the non-interesting area, was proposed. After that, some further experiments were taken to validate the new method. After comparing various accuracy indicators, such as root mean square error (RMSE), absolute mean error (MAE), 68% percentile, 95% percentile and stand deviation, the new method is showed to be better than the one that is not using the method proposed in this paper. According to our experiments, the new method is able to decrease RMSE/MAE of the tomographic image by 15% to 40%.

The adaptive filtering algorithm of GNSS/acoustic joint positioning

KUANG Yingcai, Lü Zhiping, WANG Fangchao, LI Linyang, YANG Kaichun

2020, 49(7):  854-864.  doi:10.11947/j.AGCS.2020.20190393

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The layout of seafloor control points is an important part of constructing the marine space-time frame. And the reliable marine datum positioning models and methods are the premise and basis for the layout of high-precision seafloor control points. The widely used vessel sailing surveying has both flexibility and controllability. However, there are also the inevitable abnormal disturbance effects of the vessel, which leads to the distortion of the joint positioning model of seafloor control points. To solve this problem, a GNSS/acoustic joint positioning algorithm based on adaptive weight filtering is proposed. First, the GNSS/acoustic joint positioning mathematical model for combined sea surface and underwater observation processes is derived. Then the criterion of judging the dynamic disturbance when using the adaptive filter to solve the joint positioning model is studied, and the method of constructing adaptive factors for each state parameter is given. Finally, the simulated and the measured data were used to carry out the experiment. Results show that the adaptive filtering algorithm can effectively improve the abnormal influence of state disturbance on GNSS/acoustic joint positioning, and promote its positioning stability and accuracy. When the corresponding adaptive factors of various state parameters are constructed reasonably, the best performance of the filtering effect is proved.

Application of ant colony-potential field algorithm in underwater gravity matching navigation track planning

ZHANG Chi, LI Shanshan, SHI Yanjun, XING Zhibin, FAN Diao

2020, 49(7):  865-873.  doi:10.11947/j.AGCS.2020.20190194

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The underwater submersible track in the adaptation area where the gravity characteristics change obviously can ensure the effective implementation of gravity-assisted navigation. Therefore, in the gravity matching navigation stage, the path planning of the submersible is very important. In this paper, the adaptive submarine navigation area is adaptively divided according to the gravity statistical characteristic parameters, and the adaptive and non-adaptive area labels are given. Then the artificial potential field algorithm is introduced based on the ant colony algorithm for the path planning. Reconstructing the heuristic function avoids the local optimal problem of the ant colony algorithm. At the same time, the maximum-minimum ant colony system is used to improve the pheromone update rule, which prevents the “premature” phenomenon. The simulation results show that the proposed ant colony-potential field algorithm can effectively solve the path optimization problem of underwater submersible in gravity-assisted navigation and improve the feasibility of the solution.

Photogrammetry and Remote Sensing

Real time approach for underground objects detection from vehicle-borne ground penetrating radar

YANG Bisheng, ZONG Zeliang, CHEN Chi, SUN Wenlu, MI Xiaoxin, WU Weitong, HUANG Ronggang

2020, 49(7):  874-882.  doi:10.11947/j.AGCS.2020.20190293

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Urbanization has triggered great development and changes in underground space. Exploring the types and positions of underground targets is of vital importance to urban underground security and utilization. GPRs (ground penetrating radar) are widely used in exploring underground space because of its advantages of rapid data collection, convenience, high imaging resolution and non-destructive inspection. However, the heavy manual interpretation costs of object detection from GPR limit the GPR applications in large-scale urban underground objects detection. This paper analyzes and determines seven typical types of urban road underground target that can be detected in GPR images (e.g. rainwater wells, cables, etc.). According to the characteristics of its reflected signals, the underground target in the GPR data of the 400 MHz band acquired by GSSI SIR30 in a typical urban road environment are labeled to construct the training dataset with seven categories and 3033 training samples. With the transfer learning method, the pre-trained Darknet 53 network parameters are fine-tuned, and the end-to-end YOLOV3 detection method is used to automatically extract and locate the underground targets. Finally, the experimental verification was carried out using the GPR data of the 400 MHz band collected by GSSI SIR30 in Caitian Road, Futian District, Shenzhen. Experiments show that the proposed deep learning detection method detects the buried objects from GRP data effectively, in terms of 85% of recall and precision,and the detection speed of 16FPS.

Extraction of power lines from laser point cloud based on residual clustering method

MA Weifeng, WANG Cheng, WANG Jinliang, ZHOU Jinchun, MA Yuanyuan

2020, 49(7):  883-892.  doi:10.11947/j.AGCS.2020.20190373

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Aiming at the complex environment such as missing and noise in power line cloud data, a precise power line extraction method based on model residual clustering from LiDAR point is proposed. Firstly, the near-ground points are removed according to the normalized elevation threshold segmentation. The power line points are roughly extracted using adaptive dimension features and directional features. Secondly, the improved modeling method is adopted to determine the model residual error with the constraint condition of the parabolic model. The result obtained by density clustering on the model residual error is used to extract the single power line point. Finally, the influence of the selection of key parameters on the extraction results is discussed. Two experimental results show that the method can quickly extract power line from point cloud with partial missing and noise interference, without prior knowledge such as the number of power lines and density of point cloud, etc. Which has good applicability for different types of bundle conductor extraction. the accuracy of single power line extraction is more than 99.17%, the maximum error of model fitting is 0.167 m, and the maximum mean square error of model fitting is 0.079 m.

Spatial-temporal evolution of surface deformation in grouting mining area by SMD-InSAR monitoring-analysis method

YAO Shuyi, ZHANG Yanhai, YANG Keming, SHI Xiaoyu, WANG Jian

2020, 49(7):  893-906.  doi:10.11947/j.AGCS.2020.20190430

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At present, the monitoring research of synthetic aperture radar differential interferometry (D-InSAR) in mining areas is mostly limited to taking surface movement as the object. Field measurement is usually needed to obtain other displacement deformation factors of the surface. In view of this deficiency, SMD model was constructed to map the regional surface movement and deformation(SMD). Here are the value scan besolved by SMD:①the inclination, curvature in arbitrary direction, the maximum value of inclination, curvature and its directions; ②horizontal movement and deformation of the surface in any direction in horizontal or near-horizontal coal mining, the maximum value of horizontal movement, horizontal deformation and its directions in horizontal or near-horizontal coal mining. The SMD model maps the inclination and curvature of the ground surface according to the directional derivative principle on the basis of the vertical deformation map. The horizontal movement and deformation of the surface are calculated according to the prior law of mining subsidence. The simulation experiment shows that the model can obtain the surface movement and deformation with high accuracy.SMD model combined with time-series InSAR technology was used to analyze the spatial-temporal evolution process of surface deformation and the subsidence and deformation reduction effect of grouting mining in Huaibei. The analysis showed that the grouting activity could effectively control the surface deformation. The relationship between the average grouting volume, the advancing distance of the working face and the maximum subsidence rate can be described by the multivariate linear regression model.SMD model can be used to analyze the comprehensive situation of regional surface deformation and provide a strong basis for the evaluation of the impact of mining subsidence regionally on construction.

Cartography and Geoinformation

Identification of the urban functional regions considering the potential context of interest points

CHEN Zhanlong, ZHOU Lulin, YU Wenhao, WU Liang, XIE Zhong

2020, 49(7):  907-920.  doi:10.11947/j.AGCS.2020.20190315

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The exploration of urban functional structure plays an important role in understanding urban and urban planning. POI(point of interest) data, as a representative of urban facilities, is widely used to extract urban functional areas. In the past, most of the researches on urban functional areas only considered POI statistical information. However, they ignored the abundant spatial distribution characteristics of POI, which are closely related to regional functions. Therefore, we firstly use spatial co-location pattern mining to mine the potential context of POI, extract the spatial distribution information of POI, construct regional feature vectors, and carries out the regional clustering through the clustering algorithm. Then we use the POI class ratio and residents’ travel characteristics to identify the clustering results. We experimented our method on the core urban functional areas of Beijing, the results, which were verified with Baidu Map and residents’ travel characteristics, showed that they can identify urban functional areas with obvious characteristics, such as mature entertainment business areas, science and education cultural areas, residential areas, etc. We also proved the superiority of our method compared with the LDA method based on POI semantic information and the Word2Vec method considering the linear spatial relationship of POI.

A Head-Tail information break method oriented to multi-scale representation of polyline

LIU Pengcheng, XIAO Tianyuan, XIAO Jia, AI Tinghua

2020, 49(7):  921-933.  doi:10.11947/j.AGCS.2020.20200004

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It is proposed that a multi-scale representation model of geographic polyline based on Head-Tail break of amount of information. Firstly, a geographic polyline is transformed into a Fourier shape descriptors, and the amount of information in frequency domain is defined using Shannon’s information entropy theory. Secondly, Head-Tail breaks is introduced to determine the demarcation points of information content of the polyline, and a function is designed to estimate the Fourier truncating frequency corresponding to each demarcation point. Finally, the traditional radical model based on the frequency information amount of polyline is introduced to measure the key scales and to achieve hierarchical multi-scale representation of polylines. The experiments of contour and coastline demonstrate that the model proposed can effectively simplify geographic polylines according to the set scale, and the simplification results of different target scales exist good degree of differentiation and hierarchy. At the same time, under the same overlap ratio between the simplified result and the original geographic polyline, the model proposed is better than the traditional simplification algorithm.

Summary of PhD Thesi

Research on theory and methods of satellite altimeter calibration

GUAN Bin

2020, 49(7):  934-934.  doi:10.11947/j.AGCS.2020.20190320

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Research on the monitoring and inversion of different-scale complex surface deformation with multi-temporal InSAR

LIU Yuanyuan

2020, 49(7):  935-935.  doi:10.11947/j.AGCS.2020.20190339

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Theory and method for processing the GNSS unmodeled errors

ZHANG Zhetao

2020, 49(7):  936-936.  doi:10.11947/j.AGCS.2020.20190345

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Study on the initial alignment and fault repair of GNSS/INS integrated navigation system

NING Yipeng

2020, 49(7):  937-937.  doi:10.11947/j.AGCS.2020.20190348

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Theory and methodology of multi-GNSS undifferenced and uncombined precise point positioning

ZHOU Feng

2020, 49(7):  938-938.  doi:10.11947/j.AGCS.2020.20190396

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