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    20 June 2015, Volume 44 Issue 6
    An Overview on Data Mining of Nighttime Light Remote Sensing
    LI Deren, LI Xi
    2015, 44(6):  591-601.  doi:10.11947/j.AGCS.2015.20150149
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    When observing the Earth from above at night, it is clear that the human settlement and major economic regions emit glorious light. At cloud-free nights, some remote sensing satellites can record visible radiance source, including city light, fishing boat light and fire, and these nighttime cloud-free images are remotely sensed nighttime light images. Different from daytime remote sensing, nighttime light remote sensing provides a unique perspective on human social activities, thus it has been widely used for spatial data mining of socioeconomic domains. Historically, researches on nighttime light remote sensing mostly focus on urban land cover and urban expansion mapping using DMSP/OLS imagery, but the nighttime light images are not the unique remote sensing source to do these works. Through decades of development of nighttime light product, the nighttime light remote sensing application has been extended to numerous interesting and scientific study domains such as econometrics, poverty estimation, light pollution, fishery and armed conflict. Among the application cases, it is surprising to see the Gross Domestic Production (GDP) data can be corrected using the nighttime light data, and it is interesting to see mechanism of several diseases can be revealed by nighttime light images, while nighttime light are the unique remote sensing source to do the above works. As the nighttime light remote sensing has numerous applications, it is important to summarize the application of nighttime light remote sensing and its data mining fields. This paper introduced major satellite platform and sensors for observing nighttime light at first. Consequently, the paper summarized the progress of nighttime light remote sensing data mining in socioeconomic parameter estimation, urbanization monitoring, important event evaluation, environmental and healthy effects, fishery dynamic mapping, epidemiological research and natural gas flaring monitoring. Finally, future trends of nighttime light remote sensing and its data mining have been proposed from four aspects including new data source, knowledge discovery, in-situ observation, and national/global geographic conditions monitoring.

    Newton-Gauss Algorithm of Robust Weighted Total Least Squares Model
    WANG Bin, LI Jiancheng, GAO Jingxiang, LIU Chao
    2015, 44(6):  602-608.  doi:10.11947/j.AGCS.2015.20130704
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    Based on the Newton-Gauss iterative algorithm of weighted total least squares (WTLS), a robust WTLS (RWTLS) model is presented. The model utilizes the standardized residuals to construct the weight factor function and the square root of the variance component estimator with robustness is obtained by introducing the median method. Therefore, the robustness in both the observation and structure spaces can be simultaneously achieved. To obtain standardized residuals, the linearly approximate cofactor propagation law is employed to derive the expression of the cofactor matrix of WTLS residuals. The iterative calculation steps for RWTLS are also described. The experiment indicates that the model proposed in this paper exhibits satisfactory robustness for gross errors handling problem of WTLS, the obtained parameters have no significant difference with the results of WTLS without gross errors. Therefore, it is superior to the robust weighted total least squares model directly constructed with residuals.
    The Signal Extraction of Gravity Gradient Disturbance on Moho
    YE Zhourun, LIU Lintao, LIANG Xinghui
    2015, 44(6):  609-615.  doi:10.11947/j.AGCS.2015.20140015
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    Using gravity / gravity gradient data for Moho inversion, one of the key steps is how to extract the Moho information data precisely from raw measurements. Here we mainly discussed:①In order to eliminate the error of point mass model used by GEMMA Moho research team, we choose Tesseroid in space domain and harmonic analysis and synthesis method in frequency domain; ②The reasonable use of priori crustal model. Based on GOCO03S model, we provide the gravity gradient disturbing results of three main components which are for Moho inversion. Finally, all experiment results are discussed and analyzed in this paper.
    Analysis of EnviSat Altimetric Data around Yangtze Estuary by Waveform Retracking
    PENG Fukai, SHEN Yunzhong
    2015, 44(6):  616-624.  doi:10.11947/j.AGCS.2015.20140374
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    The waveform data of EnviSat satellite (28°N~32°N, 121°E~125°E) from October 2002 to May 2010 is processed by waveform retracking methodology based on waveform classification. The waveforms in this region are classified into ocean, pre-peak, post-peak, quasi-specular and complex waveforms, with percentages of 89.03%, 2.95%, 0.45%, 3.31% and 4.26%, respectively. For each waveform, correspondent waveform retracking methodology is used. Meanwhile, it is founded that there exist system biases between the sea surface heights(SSH) calculated by different waveform retracking methodologies and calculate optimum threshold level of OCOG, threshold and sub-waveform retracker, with 65%, 45% and 50% respectively. The results of waveform retracking show that the waveform retracking methodology based on waveform classification are prior to any single retracker, which could improve the precision of SSH from 16.62% to 53.86%. In addition, the crossover discrepancies are smaller after using waveform retracking. Specifically, the crossover discrepancies of pass 089 and pass 411 are declined from 1 m to 25 cm or so and the other crossover discrepancies are all around 2~6 cm.
    Determination of Sea Ice Freeboard in Arctic from ICESat: Case Study of 2005—2006
    CHEN Guodong, LI Jiancheng, CHU Yonghai, LI Dawei
    2015, 44(6):  625-633.  doi:10.11947/j.AGCS.2015.20140478
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    Based on variation characters of sea surface height and parameters of ICESat return pulse waveform, a method is proposed for estimating Arctic sea ice freeboard with ICESat observation. This proposed method is compared with the common ‘lowest-level’ method. The results show that the lowest-level method is vulnerable to gross errors and present systematic errors in spatial distribution of freeboard. But the proposed method is more reliable than the lowest-level method. The lowest-level method is improved by the employ of an elevation standard deviation threshold and combined with the proposed method to estimate sea ice freeboard for six ICESat campaigns between 2005 and 2006 to review the seasonal variability. The results show that the abnormal climate in the summer of 2005 have a profound impact on arctic sea ice, which caused the decrease of freeboard and changed the constituent of sea ice as well.
    Relative Position Determination between Deep-space Probes Based on Same Beam Phase-referencing Imaging Technique
    ZHOU Huan, TONG Fengxian, LI Haitao, ZHENG Weimin, DONG Guangliang, LI Peijia, SHU Fengchun
    2015, 44(6):  634-640.  doi:10.11947/j.AGCS.2015.20140240
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    To meet the needs of high accuracy relative position determination in deep space explorations, a new method is proposed based on the same beam phase-referencing imaging technique that originates from the radio astronomy. Firstly, the same beam phase-referencing imaging measurement model for spacecraft positioning is built. The very long baseline interferometry (VLBI) imaging principle and the phase difference between two spacecrafts are derived. Then, two precision affecting factors are analyzed, including the signal bandwidth and the UV coverage. The dirty beams formed by different station numbers and different observation lengths with the Chinese interferometry network are simulated. Finally, with the same beam observation data of the Chang'E-3 lander and rover from the Chinese VLBI network (CVN) on December 15, 20 and 21, 2013,the Yutu rover lunar surface positions are determined with accuracy of about 1 meter. The results show the feasibility and high accuracy of this method, which is well-adapted to the spacecraft signals without special beacons.
    Single-epoch Positioning Method in Network RTK with BDS Triple-frequency Widelane Combinations
    GAO Wang, GAO Chengfa, PAN Shuguo, WANG Denghui, WANG Shengli
    2015, 44(6):  641-648.  doi:10.11947/j.AGCS.2015.20140308
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    Using the advantage that triple-frequency extra-widelane or widelane ambiguities have much longer wavelength and thus are easy to be fixed, a new network RTK (real-time kinematic) single-epoch positioning method based on BDS widelane combinations is proposed. The data processing center uses reference stations to calculate and broadcast the real-time virtual observations including double difference (DD) tropospheric and ionospheric delay correction. Then using single-satellite-pair and single-epoch mode, two extra-widelane or widelane ambiguities are resolved reliably by carrier-pseudo combination and TCAR (three-carrier ambiguity resolution) method at the rover station. Finally, the ambiguity-fixed widelane observations with the minimum observation noise and the broadcast atmospheric correction are used together to calculate the real-time kinematic positioning results. Experimental results show that the correct rates of single-epoch widelane ambiguity resolution at rover stations are larger than 99.9%. The statistical positioning error in plane is 3-4 cm, and the error in up direction is about 5 cm.
    The 2007 Ali Earthquake Inversion from Ascending and Descending InSAR Observations
    WEN Yangmao, XU Caijun, LIU Yang, FENG Wanpeng, LI Zhicai
    2015, 44(6):  649-654.  doi:10.11947/j.AGCS.2015.20140349
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    On 5th May, 2007, a Mw6.1 earthquake occurred in the Ali region, China. In this study, ascending and descending tracks of ASAR images collected by Envisat satellite are employed to derive the precise coseismic surface displacements, then nonlinear MPSO algorithm and linear least-square method with elastic half-space dislocation model are used to estimate the fault geometry and coseismic slip distribution. Our model suggests that the distributed slip mode can fit the observations very well. The earthquake fault is a normal fault with a strike of 158°, a dip of 43° and dipping to southwest. The slip mainly occurs within 7~12 km along the orientation, with a maximum slip of 0.3 m at a depth of 9 km. The determined geodetic moment is 1.24×1018 Nm, which is consistent with seismological results.
    Spherical Projection Based Straight Line Segment Extraction for Single Station Terrestrial Laser Point Cloud
    ZHANG Fan, GAO Yunlong, HUANG Xianfeng, YIN Ruojie, ZHANG Zhichao, ZHU Yixuan
    2015, 44(6):  655-662.  doi:10.11947/j.AGCS.2015.20130208
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    Due to the discrete distribution computing errors and lack of adaptability are ubiquitous in the current straight line extraction for TLS data methods. A 3D straight line segment extraction method is proposed based on spherical projection for single station terrestrial laser point clouds. Firstly, horizontal and vertical angles of each laser point are calculated by means of spherical coordinates, intensity panoramic image according to the two angles is generated. Secondly, edges which include straight line features are detected from intensity panoramic image by using of edge detection algorithm. Thirdly, great circles are detected from edges of panoramic image using spherical Hough transform. According to the axiom that a straight line segment in 3D space is a spherical great circle after spherical projection, detecting great circles from spherical projected data sets is essentially detecting straight line segments from 3D data sets without spherical projection. Finally, a robust 3D straight line fitting method is employed to fitting the straight lines and calculating parameters of the straight line segments. Experiments using different data sets and comparison with other methods show the accuracy and applicability of the proposed method.

    A Systemic Algorithm of Elliptical Artificial Targets Identification and Tracking for Image Sequences from Videogrammetry
    LIU Xianglei, TONG Xiaohua, MA Jing
    2015, 44(6):  663-669.  doi:10.11947/j.AGCS.2015.20130452
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    In order to satisfy the requirement of identification and tracking the elliptical artificial targets fast and accurately for the image sequences from videogrammetric measurement for structural health monitoring, this paper proposes a systemic algorithm to identify and track the elliptical targets using the image block technique. The proposed method extracts the image block from original images to reduce the amount of data processing for the oval targets tracking. The mathematical morphology and elliptical geometric characteristics are integrated to eliminate the non-elliptical edge information to extract the elliptical contour in the range of image block. At last, the sub-pixel center location for elliptical artificial targets is acquired by the least square algorithm. The experimental results show that RMS error of 0.025 pixel can be achieved by the proposed method, furthermore, compared with the random Hough transform and template recognition algorithm, the tracking efficiency is improved over 5 times.

    Improved Orthogonal T-Snake Model for Complex Water Boundary Extraction
    MENG Lingkui, LÜ Qifei
    2015, 44(6):  670-677.  doi:10.11947/j.AGCS.2015.20140404
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    A topology adaptive snake (T-Snake) model based on orthogonal grids is introduced and improved in this paper, and a proper energy function is designed. A detection and handling mechanism for topological conflict that caused by island shaped hollow is proposed in the model, and therefore accurate extraction for complex boundary of river containing river islands is achieved. For the disadvantage of the need to manually construct the initial contour in the orthogonal T-Snake model, using the minimum fractal dimension to obtain one area of the water and automatically generate an initial contour. The experiment shows that the algorithm of this paper can accurately extract the boundary of the complex water which contains deeply concave regions or river islands, and it has higher accuracy and less time cost than classic Snake model and GVF Snake model.

    Relational Database Extension Oriented, Self-adaptive Imagery Pyramid Model
    HU Zhenghua, MENG Lingkui, ZHANG Wen
    2015, 44(6):  678-685.  doi:10.11947/j.AGCS.2015.20140279
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    With the development of remote sensing technology, especially the improvement of sensor resolution, the amount of image data is increasing. This puts forward higher requirements to manage huge amount of data efficiently and intelligently. And how to access massive remote sensing data with efficiency and smartness becomes an increasingly popular topic. In this paper, against current development status of Spatial Data Management System, we proposed a self-adaptive strategy for image blocking and a method for LoD(level of detail)model construction that adapts, with the combination of database storage, network transmission and the hardware of the client. Confirmed by experiments, this imagery management mechanism can achieve intelligent and efficient storage and access in a variety of different conditions of database, network and client. This study provides a feasible idea and method for efficient image data management, contributing to the efficient access and management for remote sensing image data which are based on database technology under network environment of C/S architecture.

    Forest Height Inversion by Combining S-RVOG Model with Terrain Factor and PD Coherence Optimization
    XIE Qinghua, WANG Changcheng, ZHU Jianjun, FU Haiqiang
    2015, 44(6):  686-693.  doi:10.11947/j.AGCS.2015.20130731
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    The widely used random volume over ground (RVOG) model in forest height inversion with polarimetric SAR interferometric (PolInSAR) technology do not consider the effect of terrain slope. Besides, the classical and widely applied three-stage inversion method is affected by the errors about estimation of underlying topography phase and pure volume coherence. In order to correct these two types of errors, a forest height inversion strategy is proposed. On the one hand, a slope RVOG (S-RVOG) model is adopted in this paper which incorporates the range terrain slope factor to correct the terrain distortion; on the other hand, the phase diversity (PD) coherence optimization is introduced to improve accuracy of underlying topography phase estimation in line fit process and pure volume coherence estimation. In order to verify efficiency of the method, a simulation experiment is carried out by using PolInSAR data in different range slope levels simulated by PolSARpro software provided by ESA. Then, E-SAR airborne full polarization data provided by DLR are utilized to test real scenario. Finally, it is conducted that some qualitative and quantitative analyses. The results show that for the different data in different range slope levels, the inversion method promises to correct effect due to terrain distortion in RVOG model and compensate error effect in traditional three-stage inversion method. Therefore, the proposed method provides much more accurate estimation of forest parameters.

    Building the Platform of Digital Earth with Sphere Split Bricks
    WANG Jinxin, ZHENG Yasheng, LI Yaohui, LU Fengnian, LIU Junnan
    2015, 44(6):  694-701.  doi:10.11947/j.AGCS.2015.20140128
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    Discrete global grids, a modeling framework for big geo-spatial data, is always used to build the Digital Earth platform. Based on the sphere split bricks (Earth system spatial grids), it can not only build the true three-dimensional digital Earth model, but also can achieve integration, fusion, expression and application of the spatial data which locates on, under or above the Earth subsurface. The theoretical system of spheroid geodesic QTM octree grid is discussed, including the partition principle, analysis of grid geometry features and coding/ decoding method etc, and a prototype system of true-3D digital Earth platform with the sphere split bricks is developed. The functions of the system mainly include the arbitrary sphere segmentation and the visualization of physical models of underground, surface and aerial entities. Results show that the sphere geodesic QTM octree grid has many application advantages, such as simple subdivision rules, the grid system neat, clear geometric features, strong applicability etc. In particular, it can be extended to the ellipsoid, so it can be used for organization, management, integration and application of the global spatial big data.
    A General-division Grid Pattern Delaunay-TIN Parallel Algorithm
    HAN Yuanli
    2015, 44(6):  702-708.  doi:10.11947/j.AGCS.2015.20140113
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    This paper achieves out a new Delaunay triangulation algorithm. Firstly, the self-adaptation grid space division was proposed to realize the balanced logical grid division for massive point cloud data. Secondly, from far to near order the sequence of points in each grid by distance to the grid center and find out the nearest point and mark it as the central point. Thirdly, the TIN was built with by a new general-division Delaunay triangulation algorithm, which uses traditional insertion method to build TIN and add only one point from each grid at one times to form new TIN. When building TIN we use find-insertion method firstly and hereafter use topology-insertion method to keep high efficiency. This algorithm has good efficiency because it successfully avoided the merge process of sub grid triangulation mesh. Finally, the topological closure detection mechanism was established, and the independent parallel multithreading was started to model the rest points by topology-insertion algorithm limit to every grid space, which made the triangulation modeling of the whole space efficient. The method of this paper improved the support capacity of space modeling for massive point cloud data obviously.