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    20 February 2019, Volume 48 Issue 2
    Review
    Recent progress in retrieving and predicting mining-induced 3D displace-ments using InSAR
    ZHU Jianjun, YANG Zefa, LI Zhiwei
    2019, 48(2):  135-144.  doi:10.11947/j.AGCS.2019.20180188
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    This paper firstly presents the basic principle of InSAR techniques in monitoring surface deformations. Then, the existing InSAR-based approaches for retrieving mining-induced 3D displacements are classified, and their technique features and application scopes are also analyzed. Subsequently, the research progress of InSAR-based 3D deformation prediction of mining areas is demonstrated. Finally, some potential research topics in retrieving and predicting mining-induced 3-D displacements using InSAR, such as integrating multi-source data and the analysis of mining subsidence mechanism, are demonstrated.

    Geodesy and Navigation
    A precise calibration method for phase center of uplink antenna array considering its actual pointing
    LI Zongchun, LU Zhiyong, ZHANG Guanyu, LIU Bo, FENG Qiqiang, GUO Yinggang, HE Hua
    2019, 48(2):  145-152.  doi:10.11947/j.AGCS.2019.20180086
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    With regard to the inferior techniques and poor accuracy of phase center calibration of antenna array, by the power of precise engineering surveying technique, a new calibration method is proposed considering the actual antenna pointing. First of all, an industrial photogrammetric system is utilized to get the coordinates of points on antenna panels in different postures, and the actual pointing of mechanical axis is obtained by least square fitting. On this basis, the coordinates of antenna rotation center are obtained by seeking the intersection of mechanical axes with the matrix method. Finally, the mechanical axis in arbitrary postures is estimated based on inverse-angle weighting interpolation method, and the reliable phase center is obtained by moving a fixed length from the projective center alone the mechanical axis. An uplink antenna array consists of three φ3 m antennas is taken as experimental object, all photogrammetric coordinate systems are unified by the engineering control network, each antenna phase center is precisely calibrated with this proposed method. The effect of electrical signal synthesis shows that this method can effectively compensate the influence of gravity deformation and machining, and enhance the synthetic signal amplitude of uplink antenna array.

    Hotine-Helmert boundary-value calculation model for quasi-geoid determination
    MA Jian, WEI Ziqing, REN Hongfei
    2019, 48(2):  153-160.  doi:10.11947/j.AGCS.2019.20170594
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    The development of the space geodesy techniques has made it possible to obtain the ellipsoidal height, thus bringing new opportunities for the research of the second geodetic boundary value problem. The Hotine-Helmert boundary value problem, i.e. the second boundary value problem based on the Helmert's second condensation method, is studied in this paper. The definitions and algorithms for the direct and indirect topographic effects are presented at first. Then a calculation model for the Hotine-Helmert boundary value problem is presented in this contribution. The secondary indirect topographic effect on the gravity caused by the terrain condensation is unnecessary in the Hotine-Helmert boundary-value model, making it easier than the Stokes-Helmert boundary-value model. Furthermore, a kind of spheroidal Hotine kernel function whose low degrees are modified is introduced, which can effectively improve the accuracy of the quasi-geoid compared with the traditional spheroidal kernel. In order to verify the validity and practicability of the Hotine-Helmert boundary-value calculation model, the gravimetric quasi-geoid in central China with the area of 6°×4° and the resolution of 1.5'×1.5' is solved according to the Hotine-Helmert boundary-value model, using the first 360 degrees of EIGEN-6C4 model as the reference model. The accuracy of the determined gravimetric quasi-geoid in the test area is ±4.8 cm.

    Feasibility analysis of performance validation for satellite altimeters using tide gauge and deep-ocean bottom pressure recorder
    GUAN Bin, SUN Zhongmiao, LIU Xiaogang, ZHAI Zhenhe
    2019, 48(2):  161-168.  doi:10.11947/j.AGCS.2019.20170655
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    Independent of traditional approach of satellite altimeter calibration, the feasibility of altimeter validation using tide gauge located on solitary island at open sea (TGSI) and deep-ocean bottom pressure recorder (BPR) separately is initially studied. Bias of Jason-3 sea surface height (SSH) and relative SSH bias (△bias) between Jason-2 and Jason-3 is calculated using the data of tide gauge on Harvest oil platform, tide gauge No.1890000 and BPR No.21419. The standard deviations of calculated SSH bias sequence are 3.98 cm, 2.87 cm and 8.61 cm respectively, and △bias (Jason-3-Jason-2) is -3.62±2.17 cm, -2.58±1.97 cm and -2.60±1.30 cm respectively. Comparing to the results reported by foreign calibration sites, the results show that Jason-3 SSH is 3.0 cm lower than that of Jason-2. The selected BPR is appropriate to the calculation of relative SSH bias between Jason-2 and Jason-3, but it is not suitable for calibration or validation of single satellite. TGSI is appropriate to both.

    Solar radiation pressure modeling and application of BDS satellite
    CHEN Qiuli, YANG Hui, CHEN Zhonggui, WANG Haihong, WANG Chen
    2019, 48(2):  169-175.  doi:10.11947/j.AGCS.2019.20180097
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    Solar radiation pressure (SRP) model is the basis of high precise orbit determination and positioning of navigation satellites. At present, it is not uncommon for the study of SRP model of BDS satellite. However, the establishment and application of comprehensive analytical SRP model based on satellite physical parameters are rare. Different from other conservative force and non-conservative force, SRP is closely related to the satellite's physical parameters and in-orbit state, which has obviously individual differences. On the basis of the physical mechanism of solar radiation, BDS satellite physical parameters, in-orbit attitude control mode, and so on, comprehensive analytical model has been modeled in this paper. Based on precise ephemeris and laser ranging data, the precision of comprehensive analytical model has been verified. And the precision of orbit determination is decimeter using this comprehensive analytical SRP model. According to the satellite conservation theorem of angular momentum and change of in-orbit telemetry parameters, the difference between comprehensive analytical model and actual in-orbit interference force has been analyzed and calculated. The addition of empirical items on the comprehensive analytical model has been proposed in section 4. Taking C08, C10 satellite of BDS as an example, the precision of satellite laser ranging (SLR) checking precision of them is 0.078 m and 0.084 m respectively. Compared with using the improved CODE empirical model, precision orbit accuracy of them has increased by 0.021 m and 0.045 m respectively.

    Calibration for GOCE gradiometer data based on the prior gravity models
    QU Qingliang, CHANG Xiaotao, YU Shengwen, ZHU Guangbin
    2019, 48(2):  176-184.  doi:10.11947/j.AGCS.2019.20180137
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    The determination of the calibration parameters of the gravity gradiometer plays an important role in the GOCE gravity gradient data processing. In this paper, the temporal signals and outliers in the GOCE gravity gradient observations are analyzed. Based on the different global gravity field models, the scale factors and biases are determined in all the components of GOCE gravity gradients. And then the accuracy of the calibration results is validated. The results indicate that the effect of the ocean tide is at mE magnitude in the measurement band, which is equivalent to the precision of the gravity gradiometer. While the effect of the non-tide temporal signals is, with the terrestrial water is in the order of 10-4E slightly less than that of the ocean tide. The outliers in all the gravity gradient components are larger than 0.2%. After the calibration using global gravity field models except EGM96, the stability of scale factors in the Vxx,Vyy,Vzz,Vyz components reaches 10-4 magnitude. And the Vxz component reaches 10-5 while that of the Vxy component is about 10-2, which are in accordance with the accuracy differences of the gradient components.

    A simple transformation between ellipsoidal harmonic coefficients and spherical harmonic coefficients
    LIANG Lei, YU Jinhai, WAN Xiaoyun
    2019, 48(2):  185-190.  doi:10.11947/j.AGCS.2019.20180222
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    In this paper, the core idea of the conversion relationship between the ellipsoidal harmonic coefficients and the spherical harmonic coefficients is derived from the orthogonality of the Legendre function and using another coordinate variable replace the former coordinate variable in the integral expression of spherical harmonic coefficients or ellipsoidal harmonic coefficients. Then the conversion relationship between the spherical harmonic coefficient and the ellipsoidal harmonic coefficient is obtained. In addition, all the derivation of this paper is based on the squared magnitude of the ellipsoid flattening. From the conversion relationship between the ellipsoidal harmonic coefficient and the spherical harmonic coefficient, we can see that:①Using Laurent series to calculate the second type of Legendre function, it is more easier to calculate the second type of Legendre function; ②With the ε2 magnitude preserved, the derived conversion relationship is simpler than the form of literature[2] and satisfies the requirements of linearization of the physical geodetic boundary value problem; ③The difference between colatitude and reduced latitude is considered and the result is more reasonable.

    Extraction of transient aseismic creep signal monitored by dynamic GNSS
    HOU Zheng, GUO Zengzhang, DU Jiusheng
    2019, 48(2):  191-197.  doi:10.11947/j.AGCS.2019.20180261
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    Transient aseismic creep of the fault frequently induces earthquakes with high magnitude and destructiveness. In allusion to the challenges of slow sliding speed and difficult to detect, an automatic detection method of transient aseismic creep information for the fault was proposed, which based on the abnormal fluctuations of GNSS continuous coordinate time series. First, independent component analysis was used to improve the signal-to-noise ratio (SNR); then the relative strength index and kurtosis value of the fluctuations of the coordinate time series were calculated; finally a creep signal probability was converted through the cumulative distribution function, so as to the fault creep event was detected. In this paper, a 500-day GNSS surface displacement time series was simulated that included a 25-day transient creep signal. The experimental results show that the creep information of the fault can be effectively detected when the signal strength was at least equivalent to the noise level. After calculating the GNSS data for three consecutive years in the Akutan Zone, onecreep signalwas detected and it might be an aseismic creep signal related to the strong movement of the volcanic. In accordance with the processing results of seven-year GNSS data from 18 stations of the Crustal Movement Observation Network of China in Sichuan province, four abnormal signals was found. The analysis results indicated that these signals may be closely related to the abnormal displacement caused by stress accumulation and fault creep caused by the earthquake.

    Orbital elements ephemerides and interfaces design of LEO satellites
    FANG Shanchuan, DU Lan, GAO Yunpeng, ZHOU Peiyuan, LIU Zejun
    2019, 48(2):  198-206.  doi:10.11947/j.AGCS.2019.20170701
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    Low earth orbit satellites, with unique advantages, are prosperous types of navigation augmentation satellites for the GNSS satellites constellations. The broadcast ephemeris element needs to be designed as an important index of the augmented LEOs. The GPS ephemerides of 16/18 elements cannot be directly applied to the LEOs because of the poor fitting accuracies in along-track positional component. Besides, the ill-conditioned problem of the normal-matrix exists in fitting algorithm due to the small eccentricity of the LEO orbits. Based on the nonsingular orbital elements, 5 sets of ephemerides with element numbers from 16 to 19 were designed respectively by adding or modifying orbital elements magnifying the along-track and radial positional components. The fitting experiments based on the LEO of 300 to 1500 km altitudes show that the fitting UREs of the proposed 16/17/18/18*/19-element ephemerides are better than 10/6/4/5/2.5 cm, respectively. According to the dynamical range of the fitting elements, the interfaces were designed for the 5 sets of ephemerides. The effects of data truncation on fitting UREs are at millimeter level. The total bits are 329/343/376/379/396, respectively. 29/15 bits are saved for the 16/17-element ephemerides compared with the GPS16 ephemeris, while 64/61/41 bits can be saved for the 18/18*/19-element ephemerides compared with the GPS18 elements ephemeris.

    Photogrammetry and Remote Sensing
    A incremental structure from motion method of robustness enhancement and accuracy improvement
    YU Ying, ZHANG Yongsheng, XUE Wu, WANG Tao
    2019, 48(2):  207-215.  doi:10.11947/j.AGCS.2019.20170665
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    The Incremental structure from motion(ISFM) method realizes 3D reconstruction based on unordered images and plays an important role in fields such as fine modeling, 3D recording of realistic scenes and 3D reconstruction of Internet images. When facing with the complexity of the scene structure, the ISFM method has some problems, such as poor robustness and low accuracy, which often leads to unsatisfactory 3D reconstruction results and even failure of 3D reconstruction, which severely limits its development and application. An incremental structure from motion method of robustness enhancement and accuracy improvement is constucted. The main improvements are:① Facing the problem that there are many error points in stereo image feature matching, a parameter adaptive RANSAC method which takes into account the feature response value is proposed, which can effectively remove the mismatch and keep the correct matching point to the maximum extent. ② A strategy of adding the next image to avoid robustness and reconstruction accuracy is proposed, which makes the process of reconstruction more reasonable. ③ The elimination of outer points into the adjustment process is introduced, which significantly improves the robustness and accuracy of the adjustment. Finally, by using UAV low-altitude image data, close-range shooting data and Internet-downloaded image data respectively, the experimental results show that this method can effectively eliminate the mismatch points, optimize the image reconstruction sequence and weaken the effect of error points on the adjustment results.

    On-orbit geometric calibration of linear push-broom optical satellite only using sparse GCPs
    PI Yingdong, XIE Baorong, YANG Bo, ZHANG Yiling, LI Xin, WANG Mi
    2019, 48(2):  216-225.  doi:10.11947/j.AGCS.2019.20180332
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    The paper presents a geometric calibration method based on the sparse ground control points (GCPs), aiming to the linear push-broom optical satellite. This method can achieve the optimal estimate of internal and external parameters with two overlapped image pair along the charge-coupled device (CCD), and sparse GCPs in the image region, further get rid of the dependence on the expensive calibration site data. With the calibrated parameters, the line of sight (LOS) of all CCD detectors can be recovered. This paper firstly establishes the rigorous imaging model of linear push-broom optical satellite based on its imaging mechanism. And then the calibration model is constructed by improving the internal sensor model with viewing-angle model after an analysis on systematic errors existing in the imaging model is performed. A step-wise solution is applied aiming to the optimal estimate of external and internal parameters. At last, we conduct a set of experiments on ZY-3 NAD camera, and verify the accuracy and effectiveness of the presented method by comparison.

    Cartography and Geoinformation
    Run length coding and efficient compression of hexagonal raster data supported by Gosper curve
    XIN Rui, AI Tinghua
    2019, 48(2):  226-237.  doi:10.11947/j.AGCS.2019.20180216
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    By introducing the Gosper curve into hexagonal grid, a new form of run length coding is established.Based on this, the lossless compression coding and loss compression coding of raster data are carried out. First, the bidirectional correspondence between Gosper curve and hexagonal raster data is established to provide guidance and support for data coding. Then, the Gosper coding value of each raster cell is determined. The lossless compression is realized by making run length coding for the coding set of target region. On this basis, loss compression utilizes the good spatial aggregation of Gosper curve to fuse adjacent regions and eliminate details. Under certain threshold constraints and following the direction of Gosper curve, the number of coding objects can be reduced by changing the ownership of partial raster units.The data is recoded through run length coding to simply the coding of target region. At last, the validity of this method is verified by experiment. Based on the realization of compression coding methods, data compression of multi-resolution and different fusion thresholds is explored.In addition, it is compared with other methodes to highlight its advantages.

    Symbolic expressions of differences between earth radius
    ZONG Jingwen, LI Houpu, BIAN Shaofeng, TANG Qinghui
    2019, 48(2):  238-244.  doi:10.11947/j.AGCS.2019.20180145
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    A systematic and comprehensive comparison of the five commonly used earth radius in geodesy and cartography is carried out, and the differences between the most common points of the earth's radius, their corresponding maximum values, and the latitudes of equal points between themare derived with the help of computer algebraic systems. The symbolic expressionsare expressed as a power series of the first eccentricity. Taking the CGCS2000 ellipsoid as an example, the differences between the commonly used earth radii are clarified to numerical values. The results show that the difference between the commonly used Earth radii has a maximum at 90 degrees and a minimum at 0 degrees. The difference between the average radius of curvature and the equidistant sphere radius is the biggest, and the difference between the average radius of curvature and the average sphere radius is the smallest. These results can provide theoretical basis for relative research in earth science, space science, navigation and positioning.

    Marine Survey
    The key technology and application of parameter optimization combined CUBE and surface filter
    ZHAO Dineng, WU Ziyin, LI Jiabiao, ZHOU Jieqiong, ZHANG Tiansheng, LIU Yang, ZHU Chao, YU Wei
    2019, 48(2):  245-255.  doi:10.11947/j.AGCS.2019.20180082
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    CUBE (combined uncertainty and bathymetry estimator) is a widespread algorithm in the world to automatically detect and process multi-beam sounding outliers. While, little is known about its core algorithms and parameters, which is not good for the localization of this technology. In this paper, the basic principle, mathematical model, key parameters and processing steps of CUBE algorithm are elaborated. Then a method of parameter optimization selection combining CUBE and surface filter is established. And an example is presented, in which optimized parameters are selected by choosing typical bathymetric area, parameter test, comparative analysis and etc. And the optimized parameters are verified with the observed data in the Taiwan Banks. The results show that the optimized parameters can effectively improve the accuracy and efficiency of automatic processing of multi-beam data. The technology in this paper can provide reference for deepening research and development of domestic multi-beam sounding processing software and multi-beam data processing.

    Complete coverage path planning for autonomous marine vehicle used in multi-bay areas
    MIAO Runlong, PANG Shuo, JIANG Dapeng, DONG Zaopeng
    2019, 48(2):  256-264.  doi:10.11947/j.AGCS.2019.20180385
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    When using autonomous marine vehicles (AMVs) collecting seabed or hydrologicaldata, the algorithm of simple zigzag complete traversal path planning easily leads to repeated search regions and missed search regions in multi-bay ocean environment. This paper presents the environment expression concepts of repeated bay and missed bay with their points of entry, exit, and gateway. By modifying the simple zigzag complete traversal path planning algorithm using repeated-bay searching behavior and missed-bay searching behavior based on the those environment expression concepts, the new algorithm effectively reduces the area of the repeated search regions and the missed search regions for AMVs in complete traversal tasks. The efficiency and low energy consumption of the modified algorithms were tested for complete traversal path planning by computer simulation, which simulated an autonomous underwater vehicle (AUV) with known resistance characteristic in a gridding search area with a constant current velocity and flow distribution. Finally, the energy saving property and practicability of the modified algorithm were tested for complete traversal path planning on an unmanned surface vehicle (USV) in the lake.

    Summary of PhD Thesi