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Table of Content

    20 March 2022, Volume 51 Issue 3
    Geodesy and Navigation
    Spatial-temporal variations of the ionospheric TEC during the August 2018 geomagnetic storm by BeiDou GEO Satellites
    TANG Jun, GAO Xin, LI Yinjian, ZHONG Zhengyu
    2022, 51(3):  317-326.  doi:10.11947/j.AGCS.2022.20210013
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    Considering the unique geostationary characteristic of the Beidou GEO satellites, the spatial-temporal variations of ionospheric TEC during the geomagnetic storm are studied by using GEO Satellites. The global ionospheric map (GIM) is adopted as an experimental comparison. The results show that the TEC derived from the GEO satellite observations is consistent with the GIM model. Moreover, the GEO TEC can more effectively reflect subtle variations of the ionosphere. The variation and disturbance response characteristics of the ionospheric TEC are significantly different in the latitude direction during the geomagnetic storm in the Asia-Pacific region. The ionospheric TEC mainly presents positive response disturbance during the main phase of the storm in the higher latitudes of the northern and southern hemispheres, while the equatorial and lower latitude areas in the northern hemisphere both produce positive response disturbance with greater intensity and longer duration during the main phase and the recovery phase of the storm. Based on the existing studies, we think that the excitation factors of the anomalous ionospheric disturbance are the enhancement of the eastward prompt penetration electric field and neutral composition change of the thermosphere. In this paper, the experimental results suggest that GEO satellite observations can accurately and effectively monitor the anomalous variation of ionospheric TEC and the disturbance response characteristics generated by TEC at different space locations during geomagnetic storms.
    An adaptive non-uniform vertical stratification for GNSS water vapor tomography
    WANG Hao, DING Nan, ZHANG Wenyuan, FENG Zunde, ZHAO Changsheng, YAN Xiangrong
    2022, 51(3):  327-339.  doi:10.11947/j.AGCS.2022.20210126
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    GNSS tomography technique plays an important role in the monitoring and early warning of meso- and small-scale severe weather. Common GNSS tomography technique uses uniform stratification during vertical stratification, which does not consistent with the actual distribution of water vapor in the vertical direction. To resolve this problem, this paper proposes an adaptive non-uniform exponential stratification method that follows the dynamic exponential distribution of atmospheric water vapor. The proposed method greatly improves the accuracy of stratification of the tomographic model by reducing the difference in water vapor density of each layer. Moreover, it could adaptively calculate the optimal non-uniform vertical resolutions for any given tomographic region. This paper utilizes the Hong Kong Continuously Operating Reference Stations (CORS) measured data and radiosonde data in August 2019 to experiment and analyze the method. Compared with the traditional uniform stratification, the root mean squared error and the mean absolute error of the adaptive non-uniform exponential stratification are reduced by 0.40 g/m3 and 0.223 g/m3 respectively. In addition, the accuracy and quality of tomographic results are significantly improved at the lower height or in severe weather.
    A separable nonlinear least squares solution method based on Moore-Penrose generalized inverse and solid matrix
    WANG Ke, LIU Guolin, FU Zhengqing, WANG Luyao
    2022, 51(3):  340-350.  doi:10.11947/j.AGCS.2022.20200597
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    A separable nonlinear least squares algorithm based on Moore-Penrose generalized inverse and solid matrix is proposed to solve the special structure of linear combination of nonlinear functions in the field of surveying and mapping. Firstly, the variable projection algorithm is used to eliminate the linear parameters in the separable nonlinear model, and the original nonlinear optimization problem with two kinds of parameters is transformed into the least squares problem with only nonlinear parameters. Then, the first-order partial derivative of the least squares objective function is calculated based on the theory of differentiation of Moore-Penrose inverse matrix and solid matrix. Then the LM method of nonlinear optimization is used to solve the optimal estimation of nonlinear parameters. Finally, the optimal solution of linear parameters is obtained by linear least square method. The exponential model fitting experiment and airborne LiDAR full-waveform parameter solving experiment are used to compare the proposed method with the traditional optimization method without separation of parameters. The results show that the separable nonlinear least squares solution method based on the Moore-Penrose generalized inverse and the solid matrix is less dependent on the initial value of the parameter, avoids the ill-conditioned problem caused by the linear parameter in the iterative process, and the algorithm is robust. It provides a new idea for solving the separable nonlinear least squares problem in the field of surveying and mapping, and also expands the application of separable nonlinear least squares method.
    Helmert variance component estimation with non-negative constraint of covariance matrix
    WANG Leyang, ZHAO Xiong, XU Wenbin, WANG Chisheng, FANG Nan, XIE Lei
    2022, 51(3):  351-360.  doi:10.11947/j.AGCS.2022.20200333
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    How to determine the relative weight ratio in geodetic data inversion among various datasets is one of the challenging topics. In recent years, Helmert variance component estimation method (HVCE) has been widely used in the field of relative weights of joint inversion slip distributions due to its advantage of simultaneously estimating the scale factors between virtual and actual observations. However, the HVCE method sometimes suffers from the occurrence of negative variance. To overcome these problems, we propose linear inequality constraints based helmert variance component estimation method (LC-HVCE). We carry out synthetic experiment to verify the effectiveness and robustness of the LC-HVCE method and estimate the uncertainty of LC-HVCE method by Monte carlo method. We apply the proposed method to invert for the source parameters of the 2009 Mw6.3 L'Aquila earthquake (Italy). We find that LC-HVCE method is more applicable and stability than HVCE method in determining relative weight ratio and regularization parameter.
    Cartography and Geoinformation
    Continuous spatial coverage PM2.5 concentration forecast in China based on deep learning
    MAO Wenjing, WANG Weilin, JIAO Limin, LIU Anbao
    2022, 51(3):  361-372.  doi:10.11947/j.AGCS.2022.20200385
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    To achieve real-time and high-precision spatiotemporal forecast of PM2.5 concentration in China with spatial coverage is still a difficult problem. In this paper, two models based on deep learning were established to realize the spatiotemporal forecast in the hourly scale of PM2.5 concentration in China:a multi-layer long and short-term memory iterative model and an improved spatial back-propagation neural network (S-BPNN) model. First of all, we based on spatial correlation to divide 1286 air quality monitoring stations across the country in space adaptively and built a multi-layer LSTM iterative model for each region to achieve the PM2.5 concentration forecast of each monitoring site in the next 24 hours. Secondly, the improved S-BPNN spatialization model was applied to realize the refined mapping of PM2.5 concentration in a large continuous spatial coverage across the country in the next 24 hours. We integrated historical data of PM2.5 monitoring stations in China from 2016 to 2019 for training and verification. The results show that the correlation coefficients R2 of the forecast model and the spatialized model are respectively 0.88 and 0.89, indicating that the two models could achieve high accuracy. Finally, based on the proposed two models and related data crawled from monitoring stations in real-time, the intelligent online information prototype system for air pollutant concentration forecast can be built to release the forecast results of stations in real-time and display spatial results. The study has realized the real-time prediction of PM2.5 concentration with high spatio-temporal accuracy across the country and has strongly supported joint prevention and control of air pollution and public environmental spatial quality information services.
    An ensemble learning simplification approach based on multiple machine-learning algorithms with the fusion using of raster and vector data and a use case of coastline simplification
    DU Jiawei, WU Fang, ZHU Li, LIU Chengyi, WANG Andong
    2022, 51(3):  373-387.  doi:10.11947/j.AGCS.2022.20210135
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    To make use of accumulated simplification data and their contained simplification knowledge sufficiently, we propose an intelligent method based on the integration of several machine learning algorithms, which can use vector features and raster images to learn the vertex selection of polyline simplification in this paper. First, vertex selection models based on vector features and raster images are constructed by the fully connected neural network and the convolutional neural network respectively. Trained by corresponding samples, these two models can be utilized to generate vertex selection decisions via inputting vector features or raster images respectively. Second, some fusion models are constructed based on the linear weighting method, naive Bayes method, support vector machine, and artificial neural network to utilize outputs of vector-based and raster-based models to generate better decisions for vertex simplification. Finally, the proposed method applies into a use case. Experimental results show that the vector-based model and the raster-based model can learn and master vertex simplification in different levels, and fusion models can make complementary advantages of raster-based and vector-based models to improve the simplification accuracy further, and the best fusion model is better than some other simplification methods.
    Spatio-temporal information extraction method for dynamic targets in multi-perspective surveillance video
    LI Jingwen, WEI Jingshan, JIANG Jianwu, LU Yanling, LIU Lei, TANG Yifei, LI Xu
    2022, 51(3):  388-400.  doi:10.11947/j.AGCS.2022.20200507
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    As an important research direction in the field of computer vision, the precise positioning and tracking of dynamic targets in surveillance video has become a research hotspot in the surveillance field in recent years.Traditional video dynamic target detection relies only on image feature data, ignoring accurate matching with geographic coordinate systems.Especially for the area covered by multiple cameras, the spatial resolution of the image formed after projection is different when the shooting angle is different.Therefore, it is difficult to satisfy intelligent monitoring in complex geographical scenes with all-round spatio-temporal information perception.In this paper, we propose a collaborative video surveillance image and geospatial data inter-mapping model construction method to obtain spatio-temporal information such as the outline and geographic location of dynamic targets.Firstly, the mutual mapping relationship between surveillance image information and geospatial data is established, and the surveillance images with different observation angles, scales and spatial resolutions are placed under the same coordinate system.And based on this, the edge information of the target is detected by fusing Canny operator and background subtraction, and then the actual position of the target in the scene is restored by using the center-of-mass offset algorithm.This enables continuous tracking of targets under multiple angles, improves the spatio-temporal understanding and analysis of geographic scenes, and enhances the precise positioning and tracking of dynamic targets.
    Photogrammetry and Remote Sensing
    The method of GF-7 satellite laser altimeter on-orbit geometric calibration without field site
    LI Guoyuan, TANG Xinming, ZHOU Xiaoqing, LU Gang, CHEN Jiyi, HUANG Genghua, GAO Xiaoming, LIU Zhao, OUYANG Sida
    2022, 51(3):  401-412.  doi:10.11947/j.AGCS.2022.20200181
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    On-orbit geometric calibration without field site is a key problem for future multi-beam laser altimetry satellites. In view of the linear system full waveform laser altimeter loaded on the GF-7 satellite, a non-field step by step calibration method based on terrain and waveform matching is proposed. Based on the analysis of the characteristics of the GF-7 satellite laser altimeter, a rigorous geometric positioning model is constructed. The field-free on orbit geometric calibration test is carried out by using the open topographic reference data and the basic geographic information of DOM and LiDAR DSM in a certain area, which has greatly improved the accuracy of the laser altimetry data. With this method, during the first half of 2020, the calibration parameter configuration and data processing of GF-7 satellite laser altimeter was not affected, even the field calibration can't be implemented due to the negative impact of the COVID-19. The accuracy is compared with the field calibration results after the COVID-19, and the results show that the plane error of the non-field calibration is 11.597±3.693 m and the minimum value is 7.115 m. The elevation accuracy of flat area is better than 0.3 m, although it is slightly lower than the results of field calibration, it can basically meet the requirements of 1:10 000 elevation control points.
    Spaceborne lightweight image control points generation method
    JI Song, ZHANG Yongsheng, DONG Yang, FAN Dazhao
    2022, 51(3):  413-425.  doi:10.11947/j.AGCS.2022.20200203
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    In order to facilitate on-orbit processing and end-to-end mapping application of intelligent remote sensing satellite system, lightweight and on-orbit global control information has to be provided and effectively used. In this paper, a spaceborne lightweight image control points generation method is presented. Firstly, under the condition of sparse or no ground control points, global image control points are generated through the bundle adjustment of domestic high-resolution stereo mapping satellite images. Then, by describing the local image of the image control point to the feature vector, an on-board lightweight representation mode of image control points is designed, and its storage performance and on-board matching application strategies are analyzed. Finally, the Hash function obtained by hash learning is used to convert the feature vector of image control points into hash code, which can be furtherly applied to generate deep lightweight spaceborne image control points. Experiments of image control point extraction, eigenvector description, lightweight processing and matching performance analysis are completed on multi-type satellite image data in this paper. The on-orbit matching and application feasibility of lightweight image control point is verified, and abilities of lightweight global image control point are concluded.
    A performing analysis of unsupervised dense matching feature extraction networks
    JIN Fei, GUAN Kai, LIU Zhi, HAN Jiarong, RUI Jie, LI Qinggao
    2022, 51(3):  426-436.  doi:10.11947/j.AGCS.2022.20200503
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    With the development of artificial intelligence, supervised dense matching method based on deep learning has achieved good performance in virtual, indoor and driving data sets. In view of the difficulty in obtaining aerial image dense matching tag data, we use unsupervised dense matching framework for reference, and test the matching accuracy on aerial image data set and referential close range data set respectively, and realize the qualitative analysis of the relationship between network structure module and precision, which provides a further exploration of the practical application of deep learning in the field of surveying and mapping, and has important reference value. Under the same loss function condition, DispNetS, DispNetC, iResNet, GCNet, PSMNetB and PSMNetS network structures are used to test. Through analysis, the following conclusions are obtained:① Among the tested network structures, PSMNetS has the highest accuracy in aerial image data set and close range data set, and has the potential of practical application; ② The network with better performance in the supervised method may not have better performance in the unsupervised method. Its accuracy depends not only on the matching ability of the network itself, but also on the compatibility between the network and the loss function; ③ The twin network module, related information fusion module, pyramid pooling module and stacked hourglass module have good compatibility with unsupervised loss function, which can improve the network accuracy, while iResNet's image reconstruction iterative refinement module and reconstruction loss function repeat constraints, which will produce a "negative optimization" effect.
    A calibration method for navigation cameras' parameters of planetary detector after landing
    YAN Yongzhe, PENG Song, MA Youqing, ZHANG Shuo, QI Chen, WEN Bo, Li Hao, JIA Yang, LIU Shaochuang
    2022, 51(3):  437-445.  doi:10.11947/j.AGCS.2022.20200533
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    The navigation cameras of rover have been calibrated on the earth before launch, but it's a long flight before the rover arrives at another planet to work, during which the external force may cause the cameras' parameters to change. So, it is necessary to recalibrate the navigation binocular cameras after landing. This paper introduces a calibration method based on the solar panel as the calibration plate, which extracts the grid lines of the solar panel by Hough transform, the idea of clustering and least square line fitting method, and then recalibrates the external parameters of navigation binocular cameras according to the lines' parameters. At last, two experiments are carried out. In Experiment 1, the grid line extraction experiment is carried out with Chang'e 4 image, and the extraction method in this paper is more accurate compared with the traditional Hough transform line extraction results; In Experiment 2, the external parameters of binocular camera are calibrated with simulated linear parameters. The results show that the solution accuracy is high, and the method is feasible and effective. However, this camera calibration method takes the camera internal parameters as known values, and solves the external parameters of the left and right cameras separately. In the next step, we will continue to study the method of simultaneous calibration of camera internal and external parameters, and the method of one-step calibration of binocular camera.
    Fast dehaze of high resolution remote sensing images
    LIAO Zhanghui, JIANG Chuang
    2022, 51(3):  446-456.  doi:10.11947/j.AGCS.2022.20200480
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    Aiming at the problems of low utilization rate and poor effectiveness of cloud and fog remote sensing images in military aviation investigation and ground object interpretation, as well as the disadvantages of the existing cloud and fog removal algorithms, such as complex calculation, time-consuming and color distortion, combined with the characteristics of remote sensing image with small depth of field change and without sky background, an improved dark-channel prior dehazing algorithm is proposed. Firstly, the gray value of the white scene in the image is counted and the threshold is set to divide it into failure area. The water area and non water area are separated to reduce the proportion of blue band in the water area, and a new blue band is synthesized to improve the acquisition method of dark channel value; Secondly, the guided filter is used to replace the soft matting method to optimize the transmittance enhancement processing time; then, the adaptive improvement experiment of key parameters is carried out and the automatic color level restoration is adopted the color of the image after defogging. Experiments are carried out with fog UAV images and GF-2 images, and quantitative evaluation is carried out. The experimental results show that under the same experimental conditions, the processing time of a single image by this method is more than 4 times higher than that of the dark-channel prior algorithm, and the gray mean, standard deviation, information entropy and average gradient of the dehaze image are higher than those obtained by the dark-channel prior algorithm, which can effectively improve the clarity of the fogged image, Enhance image color and detail.
    E-Unet: a atrous convolution-based neural network for building extraction from high-resolution remote sensing images
    HE Zhimeng, DING Haiyong, AN Bingqi
    2022, 51(3):  457-467.  doi:10.11947/j.AGCS.2022.20200601
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    The utilization of high-resolution remote sensing images to extract urban buildings is one of the current research hotspots, but owing to the different colors, shapes and sizes of buildings, and a wide range of details, the extraction results generally suffer from blurred edges, rounded corners and loss of details. For this reason, this study proposes an E-Unet deep learning network based on cavity convolution. In the structural design, jump connections are introduced to reduce the detail loss of edges and corners; a newly designed convolution module is adopted to expand the perceptual field while reducing the number of parameters; a Dropout module is added to the bottom layer of the network to avoid overfitting; histogram equalization, Gaussian bilateral filtering and inter-band ratio operations are performed on the raw data, which are then combined into a multi-band tensor input network(without conversion to grey-scale images). To validate the network performance and clarify the reasons for the performance improvement, two sets of experiments were designed in this study on the Massachusetts and WHU building datasets. The first set of experiments is a comparison experiment between the E-Unet, Unet and Res-net networks. The results show that E-Unet not only outperforms Unet and ResNet in all accuracy evaluation metrics, but also has high fidelity in the details of the extraction results. The second set of experiments are pre-processing stripping experiments to clarify the performance improvement of the network itself and the pre-processing module. The effectiveness of the pre-processing module and the superiority of the proposed network in this research are demonstrated by the two sets of experiments.
    Summary of PhD Thesis
    Research on the multi-dimensional immovable property topological data model and modeling method
    DING Yuan
    2022, 51(3):  468-468.  doi:10.11947/j.AGCS.2022.20200473
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    Research on GNSS ionospheric scintillation monitoring and application at low latitudes
    LUO Xiaomin
    2022, 51(3):  469-469.  doi:10.11947/j.AGCS.2022.20200465
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    Research on the key technologies in water vapor retrieval using ground-based GNSS
    YANG Fei
    2022, 51(3):  470-470.  doi:10.11947/j.AGCS.2022.20200524
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    Applications of SAR interferometry for co-seismic, interseismic and volcano deformation monitoring, modeling and interpretation
    NIU Yufen
    2022, 51(3):  471-471.  doi:10.11947/j.AGCS.2022.20200528
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    Research on methods for morphological reconstruction and classification of atoll typical geomorphological units
    WANG Qi
    2022, 51(3):  472-472.  doi:10.11947/j.AGCS.2022.20200531
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    Key technologies for processing airborne LiDAR bathymetry
    SU Dianpeng
    2022, 51(3):  473-473.  doi:10.11947/j.AGCS.2022.20200542
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    Research on multi-source hybrid indoor positioning method based on RF and acoustic signal for smartphone
    GUO Guangyi
    2022, 51(3):  474-474.  doi:10.11947/j.AGCS.2022.20200552
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