Acta Geodaetica et Cartographica Sinica

Monitoring Vertical Crustal Deformation and Gravity Variations during Water Level Changes at the Three Gorges Reservoir

WANG Wei, DANG Yamin, ZHANG Chuanyin, BAI Guixia, BAO Lifeng, GAN Weijun

2017, 46(6): 671-678. doi:10.11947/j.AGCS.2017.20160331

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Monitoring vertical crustal deformation and gravity changes during water level changes at the Three Gorges reservoir is important for the safe operation of the Three Gorges Dam and for the monitoring and prevention of a regional geological disaster. In this study, we determined vertical crustal deformation and gravity changes during water level variations of the Three Gorges reservoir from direct calculations and actual measurements and a comprehensive solution. We used water areas extracted image data from the ZY-3 satellite and water level data to calculate gravity changes and vertical crustal deformation caused by every 5 m change in the water level due to storage and drainage of the Three Gorges reservoir from 145 m to 175 m. The vertical crustal deformation was up to 30 mm. The location of gravity change above 20 μ Gal(1 Gal=10^-2 m/s²) was less than 2 km from the centerline of the Yangtze River. The CORS ES13 in Badong, near the reservoir, measured the vertical crustal deformation during water level changes. Because of the small number of CORS and gravity stations in the Three Gorges reservoir area, monitoring deformation and gravity related to changes in the Three Gorges reservoir water level cannot be closely followed. Using 26 CORS and some of the gravity stations in the Three Gorges area and based on loading deformation and the spherical harmonic analysis method, an integrated solution of vertical deformation and gravity variations during water level changes of the reservoir was determined, which is consistent with the actual CORS monitoring results. By comparison, we found that an integrated solution based on a CORS network can effectively enhance the capability of monitoring vertical crustal deformation and gravity changes during water level variations of the reservoir.

Truncation Method for TSVD with Account of Truncation Bias

LIN Dongfang, ZHU Jianjun, SONG Yingchun

2017, 46(6): 679-688. doi:10.11947/j.AGCS.2017.20160268

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TSVD truncate small singular values by truncation parameter to improve the parameter estimation of ill-posed model. From the perspective of MSE (mean squared error), TSVD introduce biases to reduce variances, therefore the stability and reliability of the solution can be improved. Truncation parameter is key factor of TSVD, but it is difficult to determine in case of the gently declined singular values. The parameter determined by GCV (generalized cross-validation) and L-curve often unstable and unreliable. And the minimum MSE method is limited by the accuracy of the estimated MSE. This paper compares the changes of variance and bias produced by truncating the singular values in turn and determines the truncation parameter when the reduced variance is less than the introduced bias. In order to avoid the comparison between reduced variance and introduced bias of truncating small singular values, the confidence domain of bias is established through estimating the introduced bias of truncating big singular values that are proved to be reliable. The comparisons are replaced by comparing the reduced variance with the bias in the confidence domain. Therefore, the issue of introduced bias of truncating small singular values cannot be calculated without true values of unknown parameters is solved. Numerical examples proves the feasibility and effectiveness of the new method. Truncation parameters determined by new method are more stable and reliable than GCV and L-curve and improve the TSVD solution effectively.

Analysis of Airborne Gravity Downward Continuation Errors Effect

ZHAO Qilong, LI Jiancheng, XU Xinyu, ZHAO Yongqi, YU Nan

2017, 46(6): 689-697. doi:10.11947/j.AGCS.2017.20160390

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The variation characteristics of the random errors and systematic errors of airborne gravity (AG) are analyzed in the downward continuation (DWC) process, and then specific processing methods are presented to deal with the influence of systematic errors and random errors. Firstly, the limitation of remove-compute-recover (RCR) was generated from the RCR experiment, and it is necessary to deal with random errors and systematic errors. Systematic error effects and random error effects were calculated based on theoretical deductions and numerical simulations. The results showed the linear relationships between systematic error effects or random errors effects and grid spaces or DWC heights. It was concluded that the smaller grid spaces and higher DWC heights would increase the systematic error effects and random error effects. Ultimately, the two-step method of semi-parametric model and regularization method were proposed to estimate systematic error and to weaken random error effects. And the experimental results showed the two-step method was more effective dealing with DWC error effects than semi-parametric model and regularization method separately. Specifically, conditions of experiment were that standard deviation of random error was 2×10^-5 m/s², bias 3×10^-5 m/s²and the standard deviation of variable systematic error was about 1.3×10^-5 m/s², the DWC height was 6.3 km and the resolution was 6'. And two-step method experimental accuracy could reach about 2.3×10^-5 m/s².

Multiple Satellite Faults Detection and Identification Based on the Independent Component Analysis

ZHANG Qianqian, GUI Qingming, GONG Yisong

2017, 46(6): 698-705. doi:10.11947/j.AGCS.2017.20160079

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Considering that the independent component is sensitive to outliers, we propose an algorithm for faults detection in multivariate pseudorange time series based on independent component analysis (ICA). The threshold for outlier detection is determined through the Chebyshev inequality. Then we introduce the interventional model of time series to estimate the magnitudes of the potential satellite faults, and finally the satellite faults are identified based on the 3σ principle. In order to meet the real time requirement of receiver autonomous integrity monitoring (RAIM), a sliding window is used to transform the fault detection algorithm of the batch process into a real time one. Furthermore, a new algorithm for on line detection and identification of multiple faults is designed, and then the implementation process of the new RAIM algorithm is given. We validate the new algorithm by the civil data from 5 iGMAS monitoring stations of BeiDou in China. Examples illustrate that the new algorithm is effective in handling multiple satellite faults in real time, and the correct detection probability of faults is higher than that of the existed RANCO algorithm.

Matching Relationship between Precisions of Gravity Anomaly and Vertical Deflections in terms of Spherical Harmonic Function

WAN Xiaoyun, ZHANG Running, LI Yang, LIU Bo, SUI Xiaohong

2017, 46(6): 706-713. doi:10.11947/j.AGCS.2017.20160414

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Gravity anomalies and vertical deflections are important products of altimetry satellites. The precision indexes of them are essential for the design of future altimetry satellites. In this paper, the spherical harmonic function is used to discuss the precisions of gravity anomaly and vertical deflections. Firstly, the approximate matching relationship between gravity anomaly and vertical deflection error is deduced theoretically. Then, six ultra-high degree gravity field models are used to verify the correctness of the conclusions. The results of numerical experiments show that the errors of vertical defections and gravity anomaly satisfy the approximate proportional relation, that is, if the precision of vertical deflection is 1 μ rad, the precision of gravity anomaly is about 1.4 mGal. Conversely, if the precision of the gravity anomaly is 1 mGal, the precision of the corresponding vertical deflection is about 0.7 μ rad.

ZY3-02 Laser Altimeter On-orbit Geometrical Calibration and Test

TANG Xinming, XIE Junfeng, FU Xingke, MO Fan, LI Shaoning, DOU Xianhui

2017, 46(6): 714-723. doi:10.11947/j.AGCS.2017.20160597

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ZY3-02 is the first satellite equipped with a laser altimeter for earth observation in China .This laser altimeter is an experimental payload for land elevation measurement experiment. The ranging and pointing bias of the laser altimeter would change due to the launch vibration, the space environment difference or other factors, and that could bring plane and elevation errors of laser altimeter. In this paper, we propose an on-orbit geometric calibration method using a ground-based electro-optical detection system based on the analysis of ZY3-02 laser altimeter characteristic, and this method constructs the rigorous geometric calibration model, which consider the pointing and ranging bias as unknown systematic errors, and the unknown parameters are calibrated with laser spot's location captured by laser detectors and the minimum ranging error principle. With the ALOS-DSM data as reference, the elevation accuracy of the laser altimeter can be improved from 100~150 meters before calibration to 2~3 meters after calibration when the terrain slope is less than 2 degree. With several ground control points obtained with RTK in laser footprint for validation, the absolute elevation precision of laser altimeter in the flat area can reach about 1 meter after the calibration. The test results demonstrated the effectiveness and feasibility of the proposed method.

Object-based Morphological Building Index for Building Extraction from High Resolution Remote Sensing Imagery

LIN Xiangguo, ZHANG Jixian

2017, 46(6): 724-733. doi:10.11947/j.AGCS.2017.20170068

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Building extraction from high resolution remote sensing images is a hot research topic in the field of photogrammetry and remote sensing. In this article, an object-based morphological building index (OBMBI) is constructed based on both image segmentation and graph-based top-hat reconstruction, and OBMBI is used for building extraction from high resolution remote sensing images. First, bidirectional mapping relationship between pixels, objects and graph-nodes are constructed. Second, the OBMBI image is built based on both graph-based top-hat reconstruction and the above mapping relationship. Third, a binary thresholding is performed on the OBMBI image, and the binary image is converted into vector format to derive the building polygons. Finally, the post-processing is made to optimize the extracted building polygons. Two images, including an aerial image and a panchromatic satellite image, are used to test both the proposed method and classic PanTex method. The experimental results suggest that our proposed method has a higher accuracy in building extraction than the classic PanTex method. On average, the correctness, the completeness and the quality of our method are respectively 9.49%, 11.26% and 14.11% better than those of the PanTex.

A High Resolution Remote Sensing Image Segmentation Method by Combining Superpixels with Minimum Spanning Tree

DONG Zhipeng, WANG Mi, LI Deren

2017, 46(6): 734-742. doi:10.11947/j.AGCS.2017.20160514

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Image segmentation is the basic and key step of object-oriented remote sensing image analysis. Conventional image segmentation method is sensitive to image noise and hard to determine the correct segmentation scale. To solve these problems, a novel image segmentation method by combining superpixels with minimum spanning tree was proposed in this paper. First, the image is over-segmented by simple linear iterative clustering algorithm to obtain superpixels. Then, superpixels are firstly clustered by regionalization with dynamically constrained agglomerative clustering and partitioning algorithm using the initial segmentation number and the sum of squared deviations (SSD), local variance (LV), rate of LV change (ROC-LV) index of graphs corresponding to the segmentation number are obtained. So the suitable image segmentation number is determined according to the SSD, LV, ROC-LV index of graphs corresponding to segmentation number. Finally, superpixels are reclustered by regionalization with dynamically constrained agglomerative clustering and partitioning algorithm based on the suitable segmentation number. The experimental results showed that the proposed method can obtain good segmentation results.

A Preprocess for Change Detection Method from High Resolution Remotely Sensed Imagery in Frequency Domain

GUO Yingjie, ZHU Lanyan

2017, 46(6): 743-752. doi:10.11947/j.AGCS.2017.20160570

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At present,the efficiency of change detection from high resolution remotely sensed imagery is generally not very high, and accuracy couldn't meet the practical requirements. A method which introduced frequency domain analysis is put forward in this paper. Firstly, it studies the distribution of image frequency energy. Using it as a basis, the image division is accomplished by summed-up distance matching function. Secondly, the definition and computation of texture regularity of change information(TRCI) clearly and accurately expresses the change information according to equal energy rule of image blocks, greatly narrowing the search area. Thus, the background information could be greatly suppressed so as to improve the efficiency and precision of detection. Finally, through measuring and comparing of the accuracy and efficiency of three different detection algorithms before and after introducing the preprocess, we find that it could provides more accurate results on the existed basis.

Mining Co-location Pattern of Network Spatial Phenomenon Based on the Law of Additive Color Mixing

AI Tinghua, ZHOU Mengjie, LI Xiaoming

2017, 46(6): 753-759. doi:10.11947/j.AGCS.2017.20160324

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Mining co-location pattern is one of the hottest topics of current research in the spatial data mining community. The existing co-location mining methods belong to spatial statistics or data mining approaches, requiring much understanding of complex mathematical or statistical algorithms and parameters; and they consider events as taking place in a homogeneous and isotropic context in Euclidean space, whereas the physical movement in an urban space is usually constrained by a road network. This paper proposes a visualization method to mine co-location pattern along networks. The visual language is used to represent mutual influence between two geographic phenomena along networks. Firstly, taking Tobler's first law of geography into consideration, we use a network kernel density estimation method to express distribution pattern of geographic phenomena along networks, and construct a mapping between the distribution pattern of geographic phenomenon and color. Secondly, based on the law of additive color mixing, two colors representing two geographic phenomena are mixed to get cognition of the interaction between the two geographic phenomena. This method makes use of visual thinking, and it is intuitive and can be easily understood.

Automatic Matching of Multi-scale Road Networks under the Constraints of Smaller Scale Road Meshes

PEI Hongxing, ZHAI Renjian, WU Fang, LI Jinghan, GONG Xianyong, WU Zheng

2017, 46(6): 760-769. doi:10.11947/j.AGCS.2017.20160483

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A new method is proposed to achieve automatic matching for multi-scale roads under the constraints of the smaller scale data. Firstly, meshes should be extracted from the two different scales road data. Secondly, several basic meshes in the larger scale road network will be merged as a composite one, which will be matched with one mesh from the smaller scale road network, so that the meshes with many-to-one and one-to-one matching relationships will be matched. Thirdly, meshes from the two different scale road data with many-to-many matching relationships will be matched. Finally, road will be classified into two categories under the constraints of meshes: mesh border roads and mesh internal roads, and then matching will be done in their own categories according to the matching relationships between the two scales meshes. The results showed that roads from different scale will be more precisely matched.

Urban Intersection Recognition and Construction Based on Big Trace Data

TANG Luliang, NIU Le, YANG Xue, ZHANG Xia, LI Qingquan, XIAO Shilun

2017, 46(6): 770-779. doi:10.11947/j.AGCS.2017.20160614

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Intersection is an important part of the generation and renewal of urban traffic network. In this paper, a new method was proposed to detect urban intersections automatically from the spatiotemporal big trace data. Firstly, the turning point pairs were based on tracking the trace data collected by vehicles. Secondly, different types of turning point pairs were clustered by using spatial growing clustering method based on angle and distance differences, and the clustering methods of local connectivity was used to recognize the intersection. Finally, the intersection structure of multi-level road network was constructed with the range of the intersection and turning point pairs. Taking the taxi trajectory data in Wuhan city as an example, the experimental results showed that the method proposed in this paper can automatically detect and recognize the road intersection and its structure.

Forward and Inverse Expressions of Polar Gauss Projection without Zoning Limitations

LI Zhongmei, BIAN Shaofeng, JIN Lixin, CHEN Cheng, LIU Qiang

2017, 46(6): 780-788. doi:10.11947/j.AGCS.2017.20170009

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As traditional formulae of Gauss projection could not be used in polar regions, strict equation of complex conformal colatitude was derived with relationship between conformal colatitude and isometric latitude introduced, and then strict forward expressions of Gauss projection suit for polar regions were carried out. Based on relationship between exponential and trigonometric functions, inverse expressions of polar Gauss projection were derived by means of symbol iteration method. With reference to the forward expressions, corresponding equations of length ratio and meridian convergence for polar Gauss projection were achieved. Finally, Taking CGCS2000 ellipsoid for example, by comparing with results calculated by formulae of Gauss projection in power series forms, correctness of the proposed expressions was verified. Expressions in this paper are all free from bandwidth, and can be used in the entire poles, which could provide important references for polar mapping and navigation.

Multi-scale Representation of Digital Depth Model Based on Double Direction Rolling Ball Transform according to the Reality Principle

DONG Jian, PENG Rencan, ZHANG Lihua, LIU Guohui, ZHU Qiang

2017, 46(6): 789-801. doi:10.11947/j.AGCS.2017.20160558

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After having analyzed the application deficiency of positive direction rolling ball transform according to the safety principle, and concerned essentially with the evaluation principles of depth precision, depth order isomorphism and hierarchical nesting of terrain information for morphologic fidelity of digital depth model (DDM for short) multi-scale representation, a reality principle-compliant algorithm for DDM multi-scale representation had been proposed based on double direction rolling ball transform. Firstly, by the analysis of the variation tendency of sea floor relief feature point throughout the procedure of double direction rolling ball transform, and combined with the scale dependence character of positive direction rolling ball transform, both the traverse distribution range and the vertical distribution height of sea floor reliefs of a certain scale had been calculated. Secondly, based on the statistic characteristics of DDM grid point undulation extent, a rule of identifying detail (skeleton) reliefs had been established. Finally, by preserving the skeleton reliefs of specific scale factor, the overall trend of the changes of marine topography had been kept to meet the requirement of depth precision principle of DDM multi-scale representation. Besides, the paper demonstrated the ordered isomorphism characteristic of equidistant surface transform, and by extracting equidistant surface through double direction rolling ball transform of detail reliefs, the local undulation morphology of marine topography had been maintained to fulfill the depth order isomorphism principle of DDM multi-scale representation. Furthermore, the hierarchical nesting characteristic of terrain information in the process of double direction rolling ball transform had been demonstrated. The experiment results showed that this algorithm overcomed positive direction rolling ball transform's inability to reserve concave skeleton reliefs and preserve undulating marine topography, among its other inherent deficiencies. In addition, the algorithm preserved the hierarchical nesting of terrain information well with low terrain description uncertainty. It suggested that this algorithm could not only realize the automatic multi-scale representation of DDM but also preserve the basic terrain characteristics according to the reality principle.

Multi-task Classification of High Resolution Optic Remote Sensing Images Based on Visual Features

QI Kunlun

2017, 46(6): 802-802. doi:10.11947/j.AGCS.2017.20170081

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