Table of Content

20 January 2017, Volume 46 Issue 1

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Progresses and Prospects in Developing Marine Geodetic Datum and Marine Navigation of China

YANG Yuanxi, XU Tianhe, XUE Shuqiang

2017, 46(1):  1-8.  doi:10.11947/j.AGCS.2017.20160519

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Territorial water is a significant part of national sovereignty of China, thus the infrastructures of national space datum and location services should not only cover the land areas, but also the sea areas. China has established relatively complete geodetic datum in land areas over the past decades, including the new developed China Geodetic Coordinate System 2000 (CGCS 2000) and the national gravity datum 2000. However, the currently used geodetic infrastructures have not well covered the sea areas of China. The marine geodetic datum and marine navigation technologies need to be further developed and extended to satisfy the national demands of marine defense and marine economy development in new era of China. This paper mainly reviews the developing states and progress of Chinese marine geodetic datum and marine navigation, analyses key technologies in establishing the national marine geodetic datum. The develop current trends and future directions for the national marine geodetic datum and marine navigation technologies are listed.

Analysis of ~21.5 d Period in Ionospheric and Solar Indices during 2011

YAO Yibin, ZHANG Shun, KONG Jian

2017, 46(1):  9-15.  doi:10.11947/j.AGCS.2017.20160067

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By using Fourier transform, the spectrum of total electron content(TEC) data, relative sunspot number(RSSN), solar extreme ultraviolet(EUV) flux in 0.1~50 nm and 26~34 nm were performed to study the ~27 d period in solar-terrestrial environment. A~21.5 d period was found in TEC and solar indices, while geomagnetic indices showed no sign of this period. We infer that the ~21.5 d period could combined effects of solar rotation and active region evolution. Results of the past few solar cycles show that 21~23 d of quasi-periodic signal will appear in the rising phase of a solar cycle. Using the solar active regions located in the[-10°, 10°] slice, it is further confirmed that the ~21.5 d period observed in 2011 may be caused by the joint effects of solar active region complex and solar rotation. GIM data were used to study the global distribution of the ~27 d period oscillation.

The Rigorous Model for Similarity Transformation under Intra-frame and Inter-frame Covariance

ZENG Anmin, MING Feng

2017, 46(1):  16-25.  doi:10.11947/j.AGCS.2017.20160295

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The coordinates are obtained from observations by using least-squares method, so their precision should be contaminated by observation errors and the covariance also exists between common points and non-common points. The coordinate errors don't only exist in the initial frame but also in the target frame. But the classical stepwise approach for coordinate frame transformation usually takes the coordinate errors of the initial frame into account and overlooks the stochastic correlation between common points and non-common points. A new rigorous unified model is proposed for coordinate frame transformation that takes into account both the errors of all coordinates in both fame and inter-frame coordinate covariance between common points and non-common points, and the corresponding estimator for the transformed coordinates are derived and involve appropriate corrections to the standard approach, in which the transformation parameters and the transformed coordinates for all points are computed in a single-step least squares approach. The inter frame coordinate covariance should be consistent to their uncertainties, but in practice their uncertainties are not consistent. To balance the covariance matrices of both frames, a new adaptive estimator for the unified model is thus derived in which the corresponding adaptive factor is constructed by the ratio computed by Helmert covariance component estimation, reasonable and consistent covariance matrices are arrived through the adjustment of the adaptive factor. Finally, an actual experiments with 2000 points from the crustal movement observation network of China (abbreviated CMONOC) is carried out to verify the implement of the new model, the results show that the proposed model can significantly improve the precision of the coordinate transformation.

The Bouguer Correction Algorithm for Gravity with Limited Range

MA Jian, WEI Ziqing, WU Lili, YANG Zhenghui

2017, 46(1):  26-33.  doi:10.11947/j.AGCS.2017.20160173

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The Bouguer correction is an important item in gravity reduction, while the traditional Bouguer correction, whether the plane Bouguer correction or the spherical Bouguer correction, exists approximation error because of far-zone virtual terrain. The error grows as the calculation point gets higher. Therefore gravity reduction using the Bouguer correction with limited range, which was in accordance with the scope of the topographic correction, was researched in this paper. After that, a simplified formula to calculate the Bouguer correction with limited range was proposed. The algorithm, which is innovative and has the value of mathematical theory to some extent, shows consistency with the equation evolved from the strict integral algorithm for topographic correction. The interpolation experiment shows that gravity reduction based on the Bouguer correction with limited range is prior to unlimited range when the calculation point is taller than 1000 m.

Improvement of Narrow-lane Fractional Cycle Bias Estimation and Analysis of Its Time-varying Property

LI Linyang, CUI Yang, WANG Yupu, LÜ Zhiping

2017, 46(1):  34-43.  doi:10.11947/j.AGCS.2017.20160222

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The length of narrow-lane FCB is short, and it's seriously influenced by the quality of observation data and inaccurate models, narrow-lane FCB estimates of different reference station are significantly biased, thus the stability is relatively poor. Aiming at those biased narrow-lane FCB estimates, narrow-lane FCB robust estimation method based on robust initial value is proposed, the median of narrow-lane FCB estimates of all reference stations at current epoch is utilized as the robust initial value, and IGGⅢ scheme is applied to decrease the contribution of biased narrow-lane FCB estimates. Data from IGS global tracking stations are used in the experiment, the accuracy and stability of narrow-lane FCB are improved, the need of narrow-lane ambiguity fixing can be satisfied based on a group of daily estimated satellite narrow-lane FCB. Meanwhile, the success rate of narrow-lane ambiguity fixing and imitated dynamic positioning accuracy are improved.

Relative Calibration of Altimeters under Dual-satellite Formation Flying Altimetry Mode

GUAN Bin, SUN Zhongmiao, LIU Xiaogang, ZHAI Zhenhe

2017, 46(1):  44-52.  doi:10.11947/j.AGCS.2017.20160050

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A relative calibration method used in a novel dual-satellite formation flying altimetry mode is proposed, and a complete formula for calculating relative bias between altimeters is presented. Power spectrum analysis of each correction term in relative bias calculation formula and statistical analysis of differential sequences are respectively conducted with Jason-2 altimetry data. Under the premise that a centimeter level calibration accuracy is ensured, the formula is simplified and error budget is made. The results show that all correction items have low frequency characteristic, and the relative bias error is mainly related to the relative radial orbit error between two satellites, range error, sea state bias as well as the differential geoid height error between two comparison points. As for single overflight, the accuracy of relative bias between two altimeters is about 1.99 cm.

High Accuracy On-orbit Geometric Calibration of Geostationary Satellite GF4

WANG Mi, CHENG Yufeng, CHANG Xueli, LONG Xiaoxiang, LI Qingpeng

2017, 46(1):  53-61.  doi:10.11947/j.AGCS.2017.20160300

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GF4 satellite is the first high resolution optical geostationary satellite for remote sensing in the world, and the high accuracy geometric calibration is the key factor for the geometrical quality of satellite imagery. The positioning errors and the features of imaging region of GF4 were analyzed, the rigorous imaging model was introduced. Then on orbit calibration model and parameters estimation method were introduced for planar array sensor of GF4 satellite. The experiments used the DOM of Landsat 8 and DEM of GDEM2 for the on-orbit calibration, and the results indicated that internal accuracy of the panchromatic and near-infrared sensor and intermediate infrared sensor can be stably better than 1 pixel in the along and vertical track direction, and the absolute positioning accuracy of GF4 would be greatly affected by imaging time and imaging angle, and fluctuated remarkably.

An Adaptive Dense Matching Method for Airborne Images Using Texture Information

ZHU Qing, CHEN Chongtai, HU Han, DING Yulin

2017, 46(1):  62-72.  doi:10.11947/j.AGCS.2017.20150608

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Semi-global matching (SGM) is essentially a discrete optimization for the disparity value of each pixel, under the assumption of disparity continuities. SGM overcomes the influence of the disparity discontinuities by a set of parameters. Using smaller parameters, the continuity constraint is weakened, which will cause significant noises in planar and textureless areas, reflected as the fluctuations on the final surface reconstruction. On the other hands, larger parameters will impose too much constraints on continuities, which may lead to losses of sharp features. To address this problem, this paper proposes an adaptive dense stereo matching methods for airborne images using with texture information. Firstly, the texture is quantified, and under the assumption that disparity variation is directly proportional to the texture information, the adaptive parameters are gauged accordingly. Second, SGM is adopted to optimize the discrete disparities using the adaptively tuned parameters. Experimental evaluations using the ISPRS benchmark dataset and images obtained by the SWDC-5 have revealed that the proposed method will significantly improve the visual qualities of the point clouds.

A New Method of Coherence Optimization Based on the Phase and Coherence Magnitude in Polarimetric SAR Interferometry

LONG Jiangping, LIU Feng, DUAN Zhugeng

2017, 46(1):  73-82.  doi:10.11947/j.AGCS.2017.20150509

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The complex coherence of polarimetric synthetic aperture radar interferometry (PolInSAR) includes the magnitude and phase. The magnitude of coherence is used to measure the quality of the interference phase, and phase center represents the position of the scattering. So, how to improve the accuracy of the coherence magnitude and phase is very important for the forest parameters inversion. Maximum difference of the coherence magnitude or maximum separation of the phase, based on the coherence region, is considered partial information of the complex coherence. In this paper, a new method of coherence optimization, combined with the coherence magnitude and phase information, is established with relational degree. Applied the new approach to estimate the optimal coherence, the optimal polarimetric state of the scattering can be obtained to estimate the optimization coherence. Experimental results show that the optimal coherence criterion, jointed coherence magnitude and phase, can effectively distinguish the phase center of surface scattering and the forest canopy, and improve the reliability of the forest height inversion.

Extraction of Human Settlements from High Resolution Remote Sensing Imagery by Fusing Features of Right Angle Corners and Right Angle Sides

LIN Xiangguo, NING Xiaogang

2017, 46(1):  83-89.  doi:10.11947/j.AGCS.2017.20160389

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A method for human settlements extraction from high resolution remote sensing imagery using feature-level-based fusion of right-angle-corners and right-angle-sides is proposed in this paper. First, the corners and line segments are detected, the right-angle-corners and right-angle-sides are determined by cross verification of the detected corners and line segments, and these two types of features are rasterized. Second, a human settlement index image is built based on the density and distance of the right-angle-corners and right-angle-sides in a local region. Finally, the polygons of human settlements are generated through binary thresholding of the index image, conversion from raster format to vector format, and sieving. Three images are used for testing the proposed method. The experimental results show that our proposed method has higher accuracy than the existed method. Specifically, the correctrate, completeness, and quality of our method is higher 6.76%, 10.12%, 12.14% respectively than the existed method.

Automatic Tie Points Extraction with Uniform Distribution and High Precision

YU Ying, ZHANG Yongsheng, XUE Wu, LI Lei

2017, 46(1):  90-97.  doi:10.11947/j.AGCS.2017.20160320

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To solve the problem of matching errors, redundant points with bad distribution,and low points position precision in photogrammetry aerial triangulation,an automatic tie points extraction with uniform distribution and high precision is presented. Firstly, Block SIFT technology is conducted on every image, then an unordered feature tracking method based on union-find set is adopted to detect the multi-view correspondences. Secondly, by using the proposed algorithm of points selection in object block space, the relatively balanced points are obtained. Finally, the precision of the image coordinates are improved by least square matching.In the experiment part,Songshan images and desert images are used to test the proposed method. Through the examination and analysis of three indicators, the visual inspection, back projection errors in image space,and the precision of check points, the results show that the proposed method can effectively overcome the difficulties in extracting and matching tie points caused by weak texture and repeated texture, enhance the uniformity of tie points distribution, and improve the position precision of tie points.

Camera Self-calibration Method Based on Large Scale Aerial Images Coplanarity Constraint

ZHAO Shuang, LI Xuejun, LIU Tao, XIE Jianwei

2017, 46(1):  98-106.  doi:10.11947/j.AGCS.2017.20160206

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In this paper an automated camera self-calibration method based on large scale aerial images coplanarity constraint is proposed. The method uses stereo images corresponding points to compute camera inner parameters and the distortion coefficients based on coplanarity constraint. Firstly, aerial images corresponding points are matched and stereo images are constructed. Then the relative orientation of the camera is resolved by using the direct method and the iterative optimization based on the coplanarity constraint. Finally, the least square optimization method is used to calculate the inner parameters and the distortion coefficients of the camera. For large image the distortion of image boundary is more severe than center, in order to compute parameters more precisely mesh partition in arbitrary area of image is proposed. Compared with classical techniques which use expensive equipment or calibration field, the proposed technique can reflect the actual inner parameters of the camera in the real environment. Using all the corresponding points avoid the influence of choosing different feature points or control points on the calibration accuracy.Experimental results indicate that it is effective and flexible.The accuracy of the method is equivalent to that of calibration field, which can accurately reflect the camera parameters and the distortion coefficients of the image acquired by aerial photogrammetry.

A Kernel Density Estimation Method for Linear Features in Network Space

TANG Luliang, KAN Zihan, LIU Huihui, SUN Fei, WU Huayi

2017, 46(1):  107-113.  doi:10.11947/j.AGCS.2017.20150158

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Kernel density estimation(KDE) is an important method for analyzing spatial distributions of point features or linear features. So far the KDE methods for linear features analyze the features' spatial distributions by producing a smooth density surface over 2D homogeneous planar space, However, the planar KDE methods are not suited for analyzing the distribution characteristics of certain kinds of linear events, such as traffic jams, queue at intersections and taxi carrying passenger events, which usually occur in inhomogeneous 1D network space. This article presents a KDE method for linear features in network space, which first confirms the density distribution of each single linear feature, then computes the density distributions of all linear features in terms of distance and topology relationship in network space. This article extracts "pick-up" linear events from taxi GPS trajectory data and analyzes their distribution patterns in network space. By comparison with existing methods, experiment results show that the proposed method is able to represent the distribution patterns of linear events in network space more accurately.

An Incremental Updating Method for Land Cover Database Using Refined 2-dimensional Intersection Type

ZHOU Xiaoguang, WANG Hongsong, WU Zhiqiang

2017, 46(1):  114-122.  doi:10.11947/j.AGCS.2017.20150114

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In order to incremental updating the land cover database using the change-only information from imagery change detection methods, an vector change-only information model is designed to represent the spatial and attribute information after change, and an automatic incremental updating method for land cover database based on refined 2-dimensional intersection type is presented. As the differentiation and identification of 2-dimensional intersection type between new updates and existing objects is one of the first steps in the automatic incremental updating process for a land cover database, the 14 refined 2-dimensional intersection types are distinguished by the E-WID topological hierarchical model. Then according to the 14 refined 2-dimensional intersection types, 9 automatic updating rules for land cover database are presented. An automatic incremental updating for land cover database prototype system is developed. The effectiveness of the models and rules was verified using real data. The results of this study represent a new avenue for automatic spatial data handling in incremental updating processes.

A Geographic Weighted Regression Method Based on Semi-supervised Learning

ZHAO Yangyang, LIU Jiping, XU Shenghua, ZHANG Fuhao, YANG Yi

2017, 46(1):  123-129.  doi:10.11947/j.AGCS.2017.20150470

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Geographically weighted regression (GWR) approach will be affected by the quantity of label data. However, it is difficult to get labeled data but easy to get the unlabeled data in applications. Therefore it is indispensable to find an useful way that can use the unlabeled data to improve the regression results. As we know semi-supervised learning is a class of supervised learning tasks and techniques that also make use of unlabeled data for training typically a small amount of labeled data with a large amount of unlabeled data. So this article develops a semi-supervised-learning geographically weighted regression (SSLGWR). Firstly it builds the GWR model by labeled data. Then the unlabeled data can be calculated the value by the GWR model and they will be signed as new labeled data. Thirdly, use both labeled data and new labeled data to rebuild the GWR model to improve the model's precision. The experiments use both simulated data and real data to compare GWR COGWR and SSLGWR. Mean square error is closed as the framework to estimate the models. Experiments using simulated data have shown that the proposed model improves the performance by 39.66%, 11.92% and 0.94% relative to 10%,30% and 50% label data. And experiments using real data have shown that the proposed model improves the performance by 8.94%, 3.36% and 5.87%. The results demonstrate that there are substantial benefits of SSLGWR in the improvement of GWR.

Theory, Methodology and Application of GRACE Gravity Recovery Using Modified Short Arc Approach

CHEN Qiujie

2017, 46(1):  130-130.  doi:10.11947/j.AGCS.2017.20160470

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Research on Ship Automatic Detection Method Using Polarimetric Synthetic Aperture Radar Imagery

WEI Jujie

2017, 46(1):  131-131.  doi:10.11947/j.AGCS.2017.20160358

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Research on Land Cover and Building Target Change Detection Technology

GONG Yilong

2017, 46(1):  132-132.  doi:10.11947/j.AGCS.2017.20160478

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Method of Land Cover Web Information Discovery

HOU Dongyang

2017, 46(1):  133-133.  doi:10.11947/j.AGCS.2017.20160480

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Quantitative Assessment of the Impacts of Droughts on Grassland Productivity

LEI Tianjie

2017, 46(1):  134-134.  doi:10.11947/j.AGCS.2017.20160484

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