Acta Geodaetica et Cartographica Sinica

Positioning Accuracy Analysis of GPS/BDS/GLONASS Network RTK Based on DREAMNET

YAO Yibin, HU Mingxian, XU Chaoqian

2016, 45(9): 1009-1018. doi:10.11947/j.AGCS.2016.20160133

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With BDS being continually providing service in the Asia-Pacific Region, GLONASS being fully operational with 24 satellites in orbit again and GPS modernization, multi-GNSS network RTK will become the development trend of network RTK in the future. The data of multi-GNSS will be process by data reserving, editing and managing system of network RTK (DREAMNET), which developed independently by this research group, to analyze and compare the positioning accuracy between different combinations of global navigation satellite system. According to the experiment, the positioning accuracy of GPS/BDS/GLONASS network RTK and GPS/BDS network RTK is highest, GPS and BDS only second. Besides, with the increasing of the cut-off elevation, the availability of single GPS network RTK significantly reduces. However with 40°cut-off elevations, positioning service with the accuracy of 0.005m in horizontal, 0.025m in vertical will be provided by GPS/BDS/GLONASS network RTK in 99.84% time of a day. Finally, the statistics of positioning accuracy for 15days show that the accuracy of 0.01m in horizontal, 0.025m in vertical could be reached in six situations, which including BDS and BDS/GLONASS network RTK. Besides, the accuracy of 0.006m in horizontal, 0.015m in vertical could be reached by GPS/BDS/GLONASS network RTK, proving that the positioning accuracy and stability of DREAMNET can meet the needs of surveying and mapping.

Regional Gravity Field Modeling with Abel-Poisson Radial Basis Functions

MA Zhiwei, LU Yang, TU Yi, ZHU Chuandong, XI Hui

2016, 45(9): 1019-1027. doi:10.11947/j.AGCS.2016.20150519

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With the increasing number of various types of high-resolution gravity observations, earth gravity models can be regionally refined. We use Abel-Poisson kernel to represent the gravity as the linear summation of finite radial basis functions and combine the multiple gravity data to build a regional gravity model with high resolution. The minimum root mean square criterion based on the data adaptive algorithm is proposed to calculate the base function, which promote the speed of computation significantly. Taking the central South China Sea as an example, two different types of gravity data, namely geoid undulations with resolution of 6'×6' and gravity anomaly with resolution of 2'×2', are used to construct the high-resolution regional gravity model. The model has a resolution of 2'×2', and has a great agreement with original gravity anomaly, reaching to ±0.8×10^-5m/s².Our results show that using radial basis functions to construct the regional gravity field can avoid the problem of slow convergence of spherical harmonic functions, and can improve the resolution remarkably.

Estimation Model and Accuracy Analysis of BeiDou/GPS Real-time Precise Satellite Clock Error Integrated Resolving

CHEN Liang, GENG Changjiang, ZHOU Quan

2016, 45(9): 1028-1034. doi:10.11947/j.AGCS.2016.20150296

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Real-time high-precise satellite orbit and clock products are needed in real-time GNSS precise point positioning (PPP). In this paper, Estimation model and strategy of multi-GNSS precise satellite clock integrated resolving are researched and BeiDou/GPS real-time precise clock integrated estimation algorithm is realized by filter. Real-time simulation test results show: the STD accuracy of BeiDou/GPS real-time clock estimated in this paper compared to GFZ multi-GNSS precise clock(GBM) is about 0.15ns; horizontal accuracy after convergence of GPS kinematic PPP using simulation real-time clock products estimated in this paper is better than 5cm and vertical accuracy is better than 10cm, respectively; in BeiDou kinematic PPP test, horizontal and vertical accuracy results are same as the results using GFZ multi-GNSS precise clock(GBM) products, and the decimeter positioning can be realized.

Precision Analysis of LEO Satellite Orbit Prediction

WANG Yafei, ZHONG Shiming, WANG Haitao, OU Jikun

2016, 45(9): 1035-1041. doi:10.11947/j.AGCS.2016.20160045

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The accuracy of different fitting intervals on the predicted orbit of different arc lengths was analyzed by using the dynamic fitting method and taken HY-2A satellite as an example. According to two orbit products, one was the precise orbit obtained by CNES and the other was rapid orbit computed by adopting zero-different reduced dynamic method, obtaining the precise predicted orbit. By the results, we can get that the 3DRMS is near 6dm by using 12h or 24h fitting orbit to forecast 12h arc; the 3DRMS is near 1m when forecasting 24h arc.

Analysis of Tide Variation Monitored by GNSS-MR

ZHANG Shuangcheng, NAN Yang, LI Zhenyu, ZHANG Qin, DAI Kaiyang, ZHAO Yinghui

2016, 45(9): 1042-1049. doi:10.11947/j.AGCS.2016.20150498

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Precise monitoring of tide variation is the most of issues in the fields of Global Sea-level Observation System, ocean circulation and global climate change research. With the deepening research and rapid application of GNSS, GNSS-MR based on multipath has gradually become a new means of remote sensing for ground environment (vegetation, soil moisture, snow depth, sea level, volcano and so on) with geodetic GNSS station. By analyzing the characteristics of the onshore GNSS SNR data which is caused by multipath, the inversion principle of GNSS-MR technology based on the SNR data to detect tide variation is given in this paper. The onshore GNSS station of SC02 which is located in Friday Harbor, Washington state of United States, are used to retrieve tide variation. The retrieval result is consistent with the tide gauge which is only 359m to the GNSS station. The bias is about 10cm, and the correlation coefficient is better than 0.98. Preliminary results show that GNSS-MR technology based on onshore CORS station to some extent could be real-time and continuously used to monitor the tide variation. What's more, onshore GNSS stations could be a powerful supplement for tide gauge and be used to extend GNSS application in marine remote sensing field.

Ground Subsidence over Beijing-Tianjin-Hebei Region during Three Periods of 1992 to 2014 Monitored by Interferometric SAR

ZHANG Yonghong, WU Hongan, KANG Yonghui

2016, 45(9): 1050-1058. doi:10.11947/j.AGCS.2016.20160072

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The Beijing-Tianjin-Hebei region suffers the most serious ground subsidence in China, which has caused huge economic losses every year. Therefore, ground subsidence was listed as an important mission in the project of geographic conditions monitoring over Beijing-Tianjin-Hebei launched by the National Administration of Surveying, Mapping and Geoinformation in 2013. In this paper, we propose a methodology of ground subsidence monitoring over wide area, which is entitled "multiple master-image coherent target small-baseline interferometric SAR (MCTSB-InSAR)". MCTSB-InSAR is an improved time series InSAR technique with some unique features. SAR datasets used for ground subsidence monitoring over the Beijing-Tianjin-Hebei region include ERS-1/2 SAR images acquired between 1992 to 2000, ENVISAT ASAR images acquired between 2003 to 2010 and RADARSAT-2 images acquired between 2012 to 2014. This research represents a first ever effort on mapping ground subsidence over Beijing-Tianjin-Hebei region and over such as a long time span in China. In comparison with more than 120 leveling measurements collected in Beijing and Tianjin, the derived subsidence velocity has the accuracy of 8.7mm/year (1992—2000), 4.7mm/year (2003—2010), and 5.4mm/year (2012—2014) respectively. The spatial-temporal characteristics of the development of ground subsidence in Beijing and Tianjin are analyzed. In general, ground subsidence in Beijing kept continuously expanding in the period of 1992 to 2014. While, ground subsidence in Tianjin had already been serious in 1990s, had dramatically expanded during 2000s, and started to alleviate in recent years. The monitoring result is of high significance for prevention and mitigation of ground subsidence disaster, for making development plan, for efficient and effective utilization of water resource, and for adjustment of economic framework of this region. The result also indicates the effectiveness and reliability of the MCTSB-InSAR method. Thus, the MCTSB-InSAR method is applicable to monitoring ground subsidence over large areas in the future.

A Backward Pyramid Oriented Optical Flow Field Computing Method for Aerial Image

LI Jiatian, LI Xiankai, LI Yingyun, QIAN Tanghui, LI Guojia, LIN Yan

2016, 45(9): 1059-1064. doi:10.11947/j.AGCS.2016.20150367

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Aerial image optical flow field is the foundation for detecting moving objects at low altitude and obtaining change information. In general,the image pyramid structure is embedded in numerical procedure in order to enhance the convergence globally. However,more often than not,the pyramid structure is constructed using a bottom-up approach progressively,ignoring the geometry imaging process.In particular,when the ground objects moving it will lead to miss optical flow or the optical flow too small that could hardly sustain the subsequent modeling and analyzing issues. So a backward pyramid structure is proposed on the foundation of top-level standard image. Firstly,down sampled factors of top-level image are calculated quantitatively through central projection,which making the optical flow in top-level image represent the shifting threshold of the set ground target. Secondly,combining top-level image with its original,the down sampled factors in middle layer are confirmed in a constant proportion way. Finally,the image of middle layer is achieved by Gaussian smoothing and image interpolation,and meanwhile the pyramid is formed. The comparative experiments and analysis illustrate that the backward pyramid can calculate the optic flow field in aerial image accurately,and it has advantages in restraining small ground displacement.

A Structure Feature for Automatic Extraction of Plantation from High-resolution Remote Sensing Imagery

YAN Li, JIANG Weiwei

2016, 45(9): 1065-1072. doi:10.11947/j.AGCS.2016.20150511

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Satellite remote sensing is an invaluable tool to manage land resources. However, data analysis procedures should satisfy the good adaptability, wide application prospects and high accuracy levels demanded by users. This study presented a novel multi-scale and multi-direction structure index (MMI) to describe the structure feature of plantation caused by cultivation. Plantation are extracted by performing a threshold on the MMI feature map, and combined with morphological operators to refine the extraction results. We designed three groups of experiments to test our method, each group used panchromatic and multispectral imagery respectively with various cultivation mode, different vegetated background and structure complexity. The results show our method is much more adaptive on plantation extraction than traditional methods. It is efficient for various complex plantations, e.g. multi-direction, multi-scale, highly vegetated backgrounds, low regularity of planting mode with deformation of textons and planting lines, the accuracy results exceed 90%. And panchromatic images achieve accuracies as high as multispectral images, which indicate our method has low dependence on spectrum, thus it is more flexible for data selection and application.

Combined Saliency with Multi-Convolutional Neural Network for High Resolution Remote Sensing Scene Classification

HE Xiaofei, ZOU Zhengrong, TAO Chao, ZHANG Jiaxing

2016, 45(9): 1073-1080. doi:10.11947/j.AGCS.2016.20150612

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The scene information existing in high resolution remote sensing images is important for image interpretation and understanding of the real world. Traditional scene classification methods often use middle and low-level artificial features, but high resolution images have rich information and complex scene configuration, which need high-level feature to express. A joint saliency and multi-convolutional neural network method is proposed in this paper. Firstly, we obtain meaningful patches that include dominant image information by saliency sampling. Secondly, these patches will be set as a sample input to the convolutional neural network for training, obtain feature expression on different levels. Finally, we embed the multi-layer features into the support vector machine (SVM) for image classification. Experiments using two high resolution image scene data show that saliency sampling can effectively get the main target, weaken the impact of other unrelated targets, and reduce data redundancy; convolutional neural network can automatically learn the high-level feature, compared to existing methods, the proposed method can effectively improve the classification accuracy.

Remote Sensing Images Super Resolution Reconstruction Based on Multi-scale Detail Enhancement

ZHU Hong, SONG Weidong, TAN Hai, WANG Jingxue

2016, 45(9): 1081-1088. doi:10.11947/j.AGCS.2016.20150451

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The existing methods are hard to highlight the details after super resolution reconstruction, so it is proposed a super-resolution model frame to enhance the multi-scale details. Firstly, the sequence images are multi-scale deposed to keep the edge structure and the deposed multi-scale image information are differenced. Then, the smoothing information and detail information are interpolated, and a texture detail enhancement function is built to improve the scope of small details. Finally, the coarse-scale image information and small-medium-scale information are confused to get the premier super-resolution reconstruction result, and a local optimizing model is built to further promote the premier image quality. The experiments on the same period and different period remote sensing images show that the objective evaluation index are both largely improved comparing with the interpolation method, traditional total variation(TV)method,and maximum a posterior(MAP) method. The details of the reconstruction image are improved distinctly. The reconstruction image produced using the proposed method provides more high frequency details, and the method proves to be robust and universal for different kinds of satellite remote sensing images.

Adaptive Three-component Decomposition Approach for Polarimetric SAR Data

CAI Yongjun, ZHANG Xiangkun, JIANG Jingshan

2016, 45(9): 1089-1095. doi:10.11947/j.AGCS.2016.20150533

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In this paper, the problems such as negative power and scattering mechanism ambiguity in original polarimetric SAR three-component decomposition are introduced, and the remaining flaws in its improved approaches are in depth analyzed. Based on these, an adaptive three-component decomposition is proposed, and more generalized scattering models are used. Because in one pixel there may exist two odd or double bounce scattering targets with different orientation angels, the proposed method firstly considers this situation, so that the surface and double bounce scattering can be preserved more sufficiently. And then the alpha parameter is used to identify the dominant scattering except for the volume scattering. Lastly, an optimization measure to the pixels with negative power is proposed, which significantly decreases the negative power pixels count, so the decomposition will be more accurate and more valid. The results show great improvements in real scattering characteristics extraction and the flaws in model based decomposition approaches can be better resolved.

SAR Image Coastline Detection Based on Regional Distance Regularized Geometric Active Contour Models

JIANG Dawei, FAN Jianchao, HUANG Fengrong

2016, 45(9): 1096-1103. doi:10.11947/j.AGCS.2016.20160039

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Synthetic aperture radar (SAR) satellite remote sensing images can greatly increase the frequency of the coastline coverage all over the country. However, due to the influence of the random sea surface roughness caused by waves, it's a challenge to distinguish the coastline and sea boundary. To solve this problem, this paper proposes regional distance regularized geometric active contour models (RDRGAC), in which the distance regularized term is introduced to avoid periodically initializing the degraded function with a signed distance function, accelerating the speed of convergence. Besides, it establishes the nonlinear regression relationship between the regional term parameters and equivalent number of looks (ENL) in SAR images, leading to the adaptive setting of RDRGAC model with different SAR images, which could improve the accuracy of coastline automatic detection in return. In the experiments, SAR images in Beidaihe and Dalian Jinzhou Bay respectively are adopted to detect the coastline, verifying the effective of the proposed method.

A Waterline Extraction Method from Remote Sensing Image Based on Quad-tree and Multiple Active Contour Model

YU Jintao, GUO Haitao, LI Chuanguang, LU Jun, JIANG Chunxue

2016, 45(9): 1104-1114. doi:10.11947/j.AGCS.2016.20160037

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After the characteristics of geodesic active contour model (GAC), Chan-Vese model(CV) and local binary fitting model(LBF) are analyzed, and the active contour model based on regions and edges is combined with image segmentation method based on quad-tree, a waterline extraction method based on quad-tree and multiple active contour model is proposed in this paper. Firstly, the method provides an initial contour according to quad-tree segmentation. Secondly, a new signed pressure force(SPF) function based on global image statistics information of CV model and local image statistics information of LBF model has been defined, and then ,the edge stopping function(ESF) is replaced by the proposed SPF function, which solves the problem such as evolution stopped in advance and excessive evolution. Finally, the selective binary and Gaussian filtering level set method is used to avoid reinitializing and regularization to improve the evolution efficiency. The experimental results show that this method can effectively extract the weak edges and serious concave edges, and owns some properties such as sub-pixel accuracy, high efficiency and reliability for waterline extraction.

A Schematic Method Based on the Integration of Stroke Construction and Displacement for Road Network

FU Zhongliang, WENG Baofeng, HU Yulong

2016, 45(9): 1115-1121. doi:10.11947/j.AGCS.2016.20160080

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In current map schematization methods, the degree of simplification is not enough, the length of information is not considered, and time efficiency is low. This study aims to track these problems and a schematic method based on the integration of stroke construction and displacement for road network is proposed.The method constructs strokes for road network, at the same time to make displacement and topology check. Simultaneously, this study uses similar fractal dimension to quantitatively compare and evaluate the effectiveness of different schematic methods. The experimental results indicated that the new method takes into account the original alignment and makes the process simply. The method has more effective in time and reduces topological confliction problem to maintain topological consistency and balance the road network. Finally, the schematic map has great clarity and well-preserved map recognition.

Visualization and Extraction of Trajectory Stops Based on Kernel-density

XIANG Longgang, SHAO Xiaotian

2016, 45(9): 1122-1131. doi:10.11947/j.AGCS.2016.20150347

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Trajectory stops imply important semantic information, and the extraction of trajectory stops is the premise to carry out advanced Stop/Move analysis. This paper, based on the idea of kernel density, firstly introduces the concept of stop index, which is derived by cumulating spatio-temporal contribution of neighboring points, and further designs stop index graph to intuitively visualize the evolution of spatio-clustering degree during a trajectory. Importantly, stops index and its graph are related to spatial scale through neighboring radius, which then can be exploited to analyze trajectory stops under multiple scales. In addition, this paper introduces stop sequence rooted from stop index, and proposes an algorithm for the automatic extraction of trajectory stops by progressively merging stop sequences. According to the algorithm, a stop under strong GPS signal exactly corresponds to a stop sequence, while a stop under weak GPS signal could be derived by merging multiple stop sequences. Experiments based on own-acquired and GeoLife trajectories show that the algorithm has achieves the balance between the completeness and accuracy of stop extraction, and could effectively discover and extract complex and diverse trajectory stops. Even facing trajectories with serious drift noises, the algorithm still achieves a high rate of accuracy on stop extraction.

Development of Lunar Spacecraft Precision Orbit Determination Software System and Research on a Four-way Relay Tracking Measurement Mode

YE Mao

2016, 45(9): 1132-1132. doi:10.11947/j.AGCS.2016.20160339

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