Table of Content

20 February 2017, Volume 46 Issue 2

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Estimation of BDS DCB Combining GIM and Different Zero-mean Constraints

YAO Yibin, LIU Lei, KONG Jian, FENG Xinying

2017, 46(2):  135-143.  doi:10.11947/j.AGCS.2017.20160375

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As the limited number of the BeiDou Navigation Satellite System (BDS) satellites and tracking stations currently, it's difficult to attain daily DCBs solution with precisely high accuracy based on BeiDou single system. In order to overcome the weakness above, two different zero-mean constraints for BDS satellites, called constraint one and constraint two, respectively, are used to estimate DCBs of BDS based on BeiDou observations from the multi-GNSS experiment (MGEX) network and global ionosphere maps (GIM) from the Center for Orbit Determination in Europe (CODE). The results show that the systematic difference of the overall trend under two different constraints is consistent, and the systematic difference of DCB_C2I-C7I and DCB_C2I-C6I is -3.3 ns and 1.2 ns, respectively. The systematic difference between BDS satellite DCBs and receiver DCBs has the same absolute value, but opposite signs instead. Compared to constraint one, The DCBs estimation of IGSO/MEO satellites under constraint two are more stable (the improvement of satellites DCB_C2I-C7I and DCB_C2I-C6I STD are up to 21%, 13%, respectively), the stability of IGSO and MEO satellites (STDs are within 0.1 ns, 0.2 ns, respectively) is better than that of GEO satellites (STDs are 0.15~0.32 ns). DCB estimation of constraint one is not only consistent with the CAS/DLR products (Bias:-0.4~0.2 ns), but also takes into account the stability of BDS satellites DCB. Under the two different constraints, there is no obvious change in BDS receiver DCBs, meaning that the selection of constraints has no obvious influence on the stability of BDS receivers DCBs. The overall stability of BDS receiver DCBs is better than 1 ns. Due to the accuracy discrepancy of GIM in different latitudes, the stability of BDS receiver DCBs in the middle-high latitude (STDs are within 0.4 ns) is better than that in low latitude region (STDs are 0.8~1 ns).

Research on the Real-time Compensation of the Fiber Optic Gyroscope Random Drift in Airborne Vector Gravimetry

WANG Zheng, LI Jiancheng

2017, 46(2):  144-150.  doi:10.11947/j.AGCS.2017.20160174

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Random drift error of fiber optic gyroscope is the crucial factor that influences the calculation accuracy of the attitude of airborne vector gravimetry. Modeling and compensating it can restrain this type of error significantly. Given the problem that traditional ARMA model can be only applied in the case of stable random drift, which cannot meet the need of real-time filtering, an ARIMA model (autoregressive integrated moving average) which is suitable for non-stable random drift is introduced along with the detailed procedure in this paper. The algorithm that can eliminate the constant component of original sampling sequence with real-time averaging method is also proposed as well as the real-time Kalman filtering estimation of the random drift. With the methods proposed above, the variance of random drift can be reduced by 46.5%. The analysis of Allan variance suggests that the coefficients of random drift for angle and angular speed have decreased about 50% and 40%, respectively. The results showed that non-stable random drift can be accurately characterized by ARIMA model and that online estimation of random drift can be realized by real-time average algorithm, indicating the potential to improve the calculation accuracy of the attitude of airborne vector gravimetry.

Waveform Retracking and Emulation Experiment Analysis of Synthetic Aperture Radar Altimeter

ZHAI Zhenhe, SHI Lingwei

2017, 46(2):  151-156.  doi:10.11947/j.AGCS.2017.20160213

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Based on the synthetic aperture radar(SAR) convolution model, the convolution computation formula about the derivative of three parameters of time migration, rise time and amplitude are deduced. The SAR waveform retracking is completed using numerical integration and Fourier transform. Besides, the echo waveform under SAR model is generated using the simulation orbit, troposphere, ionosphere and tide model. The comparison shows that the shape of echo waveform under SAR model is the same as that of CryoSat-2 1 Hz SAR. The experiments show that the accuracy of SAR altimeter retracking is about 5 cm under the 20 Hz data(about 350 m resolution), which are improved compared with that of the traditional model.

The Long-term Performance Analysis for On-board Atomic Clocks of BDS

WANG Yupu, LÜ Zhiping, WANG Ning

2017, 46(2):  157-169.  doi:10.11947/j.AGCS.2017.20160369

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BeiDou Navigation Satellite System (BDS) has begun to provide regional services since the end of 2012. It plays an important role in analyzing the long-term performance of BDS satellite clocks in evaluating the performance of the whole system, determining and predicting satellite clock bias (SCB) etc. Precise satellite clock data products derived from multi-satellite orbit determination are used to conduct the performance analysis of BDS satellite clocks. Specifically, the characteristics of SCB data are discussed by using a proposed modified median absolute deviation (MAD) to preprocess original SCB data. Long-term variations of satellite clocks' phase, frequency, frequency drift and model noise level are analyzed based on the quadratic polynomial SCB model. Frequency stability of BDS satellite clocks is calculated and discussed based on Overlapping Hadamard Variance. Periodicity of BDS SCB is analyzed by using spectral analysis method. Integrating the above mentioned discussions and corresponding experiment results, the long-term performance of BDS satellite clocks is relatively comprehensively evaluated and analyzed. In addition, some valuable conclusions are obtained. For example, in the aspects of noise characteristics and clock drift, the performance of MEO satellite clocks is the best, followed by the IGSO satellite clocks, and the GEO satellite clocks' performance is the worst. The average values of noise level and frequency drift of BDS satellite clocks are respectively 0.677 ns and 1.922×10^-18. There are also obvious periodic terms in BDS SCB data derived from multi-satellite orbit determination and their primary periods are approximate equal or one-half to the corresponding satellite orbit periods. The average value of frequency stability of BDS satellite clocks is 1.484×10^-13.

Measuring Terrestrial Water Storage Change Using GRACE, GPS and Absolute Gravity Data in Scandinavia

JIA Lulu, WANG Hansheng, XIANG Longwei

2017, 46(2):  170-178.  doi:10.11947/j.AGCS.2017.20160272

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Gravity satellite GRACE-derived terrestrial water storage change would be seriously affected by glacial isostatic adjustment(GIA) in Scandinavia. To solve this problem, it is calculated that the measured linear ratio of GIA gravity rates and vertical displacement rates according to the data from collocation stations for absolute gravity and GPS. Using the linear ratio and uplift field derived from GPS observation network, the gravity signal of GIA is got. Gravity change rates from GRACE RL05 data can be corrected for GIA using independent gravity rates derived from GPS vertical velocities, and then it is calculated that corresponding equivalent water thickness in Scandinavia and the uncertainties are evaluated by considering the uncertainties from data. The proposed method utilizes observational data only and can avoid the enormous uncertainty from GIA models.The results are compared with that of two hydrological models. The ratio of gravity versus uplift obtained by ground-based measurements in Scandinavia is 0.148±0.020 μGal/mm(1 Gal=10^-2 m/s²), which validates Wahr's approximate theoretical ratio and is very close to the result from North America. From January 2003 to March 2011, terrestrial water storage shows obvious increase in Scandinavia. The main signal locates at the Vänern lake which is in the southern tip of the peninsula. The rate of total water storage is 4.6±2.1 km³/a and the corresponding cumulative quantity is 38±17 km³ for the period 2003 to 2011. Results from hydrological models are consistent with the result very well. The correlation coefficient between GRACE and WGHM hydrological model can reach 0.69, while for GLDAS model the correlation coefficient is slightly smaller.

Combined Positioning of TerraSAR-X and SPOT-5 HRS Images with RFM Considering Accuracy Information of Orientation Parameters

CHENG Chunquan, ZHANG Jixian, HUANG Guoman, ZHANG Li, YANG Jinghui

2017, 46(2):  179-187.  doi:10.11947/j.AGCS.2017.20160138

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RFM is suitable for geometric positioning with multi-source images because of the independence of sensors. However, without GCPs the geometric advantages from the geometrically prevailing images cannot be enforced in the traditional RFM-based orientation. It also leads to the apparent flaw of divergence of solving. By translating the priori information of autonomous positioning accuracy and imaging drift errors to bias compensation parameters in image space, it is rebuild a new RFM-based adjustment model which considers the accuracy and weight of the orientational parameters. A test study of positioning without GCPs which includes 12 scenes of TerraSAR-X images and 6 pairs of long-strip stereo SPOT-5 HRS images covering area of 186 000 km² is conducted. Furthermore, the different impact factors on positioning accuracy, i.e., the accuracy of orientation parameters, the number of SAR image, orbit direction of SAR satellite and distribution of SAR images, are investigated. The results show that it can achieve positioning accuracy of 6.0 m in plan and 4.2 m in height for the case of geometrical combination of TerraSAR-X and HRS images. The proposed model is superior to the traditional RFM-based positioning with respect to accuracy and resolving stability. It is a potential approach for worldwide mapping at scale of 1:100 000 and 1:50 000 without GCPs by combination of different satellite images.

A Fast and Effective Block Adjustment Method with Big Data

ZHENG Maoteng, ZHANG Yongjun, ZHU Junfeng, XIONG Xiaodong, ZHOU Shunping

2017, 46(2):  188-197.  doi:10.11947/j.AGCS.2017.20160293

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To deal with multi-source, complex and massive data in photogrammetry, and solve the high memory requirement and low computation efficiency of irregular normal equation caused by the randomly aligned and large scale datasets, we introduce the preconditioned conjugate gradient combined with inexact Newton method to solve the normal equation which do not have strip characteristics due to the randomly aligned images. We also use an effective sparse matrix compression format to compress the big normal matrix, a brand new workflow of bundle adjustment is developed. Our method can avoid the direct inversion of the big normal matrix, the memory requirement of the normal matrix is also decreased by the proposed sparse matrix compression format. Combining all these techniques, the proposed method can not only decrease the memory requirement of normal matrix, but also largely improve the efficiency of bundle adjustment while maintaining the same accuracy as the conventional method. Preliminary experiment results show that the bundle adjustment of a dataset with about 4500 images and 9 million image points can be done in only 15 minutes while achieving sub-pixel accuracy.

Compareison of the Accuracy of Incremental SFM with POS-aided Bundle Adjustment

XUE Wu, ZHANG Yongsheng, ZHAO Ling, YU Ying, WANG Tao, LI Lei

2017, 46(2):  198-207.  doi:10.11947/j.AGCS.2017.20160274

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An accuracy comparison research was conducted between the incremental structure from motion in computer vision and the POS-aided bundle adjustment in photogrammetry. Firstly, the basic principle and workflow of SFM were introduced, and the similarities and differences between the two methods were analyzed theoretically. Then the positioning accuracy was compared, using the unmanned helicopter and manned aircraft aerial survey data in the Songshan remote sensing calibration field. Experimental results show that without POS data, the incremental structure from motion method can achieve equivalent accuracy to the POS-aided bundle adjustment. Both methods can meet the requirement of 1:500 and 1:1000 mapping. Finally, suggestion was proposed for aerial data post-processing according to different operational requirements.

Hierarchical Remote Sensing Image Matching Method Based on Free-form Linear Features

CHEN Xiaowei, ZHANG Baoming, GUO Haitao, ZHAO Chuan, XU Junfeng

2017, 46(2):  208-217.  doi:10.11947/j.AGCS.2017.20160282

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A remote sensing image matching method using the hierarchical matching strategy is proposed, with the purpose of resolving the conflict between the full use and effective description of the rich information of free-form linear feature (FFLF) in the study of FFLF matching. To ensure high matching precision, continuous FFLFs are extracted based on sub-pixel edge detection and tracing method. In the coarse matching process, closed linear features (CLF), linear feature intersection (LFI) and corner (LFC) were selected as conjugated entities. After determining candidate features, the false matching was gradually eliminated based on area, angle and other geometry information as well as the distribution characteristics of the model parameters determined by feature combinations, finally the initial value of accurate matching was determined by the conjugate features. In the accurate matching process, based on multi-level two-dimensional iterative closest point (ICP) method, sub-pixel edge points with the sampling rate from low to high were orderly used for matching. Experimental results show that the features selected for coarse matching have stable performance. Coarse matching is of high accuracy and precision and can provide high precision initial matching parameters for accurate matching. Accurate matching can reach sub-pixel level precision equal to the least square matching (LSM) and with good adaptability to small image affine transformation.

A Line Extraction Method for Chain Code Tracking with Phase Verification

DAI Jiguang, ZHANG Li, LI Jinwei, FANG Xinxin

2017, 46(2):  218-227.  doi:10.11947/j.AGCS.2017.20160303

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A line extraction method for chain code tracking with phase verification was proposed in this study. Firstly, a complete refinement algorithm targeting the Canny edge map was presented. Secondly, an improved chain code tracking method was proposed, and the key algorithm steps were described as follows:detecting the start points of chain code; setting up dynamic main directions to determine the tracking directions of chain code; tracking edge points inside the eight neighborhoods was preferred, and then edge points outside the eight neighborhoods if no edge points existed inside the eight neighborhoods, meanwhile linear analysis was employed to perform dynamic constraints on the chain code. Finally, linear fitting and phase marshalling validation were processed upon the chain code tracking, where straight lines were output when condition were satisfied, otherwise the start points of chain code should be reset to extract straight lines. The experimental results from a variety of different optical image data showed that the proposed algorithm could not only achieve precise fit straight edge information, but also solve the linear fracture problems induced by white noise and phase grouping.

The Purification Method of Matching Points Based on Principal Component Analysis

DONG Yang, FAN Dazhao, JI Song, LEI Rong

2017, 46(2):  228-236.  doi:10.11947/j.AGCS.2017.20160250

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The traditional purification method of matching points usually uses a small number of the points as initial input. Though it can meet most of the requirements of point constraints, the iterative purification solution is easy to fall into local extreme, which results in the missing of correct matching points. To solve this problem, we introduce the principal component analysis method to use the whole point set as initial input. And thorough mismatching points step eliminating and robust solving, more accurate global optimal solution, which intends to reduce the omission rate of correct matching points and thus reaches better purification effect, can be obtained. Experimental results show that this method can obtain the global optimal solution under a certain original false matching rate, and can decrease or avoid the omission of correct matching points.

The Extraction of Road Boundary from Crowdsourcing Trajectory Using Constrained Delaunay Triangulation

YANG Wei, AI Tinghua

2017, 46(2):  237-245.  doi:10.11947/j.AGCS.2017.20160233

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Extraction of road boundary accurately from crowdsourcing trajectory lines is still a hard work.Therefore,this study presented a new approach to use vehicle trajectory lines to extract road boundary.Firstly, constructing constrained Delaunay triangulation within interpolated track lines to calculate road boundary descriptors using triangle edge length and Voronoi cell.Road boundary recognition model was established by integrating the two boundary descriptors.Then,based on seed polygons,a regional growing method was proposed to extract road boundary. Finally, taxi GPS traces in Beijing were used to verify the validity of the novel method, and the results also showed that our method was suitable for GPS traces with disparity density,complex road structure and different time interval.

The Recognition of Overpass in Volunteered Geographic Information

MA Chao, SUN Qun, CHEN Huanxin, XU Qing, YANG Hui

2017, 46(2):  246-252.  doi:10.11947/j.AGCS.2017.20160070

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The paper presents an overpass recognition method in volunteered geographic information based on the geometry and attribute characteristics. The structure of the overpass is divided into the main bridge parts and the affiliated facilities. The main bridge parts with distinctive characters could be treated as a two-class classification problem. The characteristic vectors could build on the foundation of analysis and quantization the geometry and attribute characteristics. Then, the main bridge is recognized automatically through the support vector machine. The affiliated facilities of the overpass are recognized based on the main bridge with some relevant judgment rules. The OpenStreetMap(osm) is selected for the experiment. The results show that the method could effectively recognize the overpass and could provide help for the road simplification and walking guidance.

An Efficient Approach to Shape Reconstruction from Planar Point Set Based on Multi-constraints

ZHU Jie, SUN Yizhong

2017, 46(2):  253-264.  doi:10.11947/j.AGCS.2017.20160122

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An efficient algorithm to boundary representation from a planar point set in order to adapt the complexity of spatial distribution was presented in this paper. At first, an appropriate and practical data structure was designed to express geometric information and topological information, which provides an easy access to links embedded in DT serving as a basis for the filtering procedures; then the algorithm generates rough boundary based on an iterative removal of Delaunay triangulation. Furthermore, a mathematic formulation for cavities and holes was given and a statistical method to detect them was designed. Finally, a series of experiments including both simulated and real data sets to validate the effectiveness and practicability of our algorithm was conducted.

Study on Application and Comparison of Data-driven Model and Semi-data-driven Model for Rainfall-runoff Simulation

KAN Guangyuan

2017, 46(2):  265-265.  doi:10.11947/j.AGCS.2017.20160502

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Research on Semantic Analysis and Computing Model for Geographic Instance

TAN Yongbin

2017, 46(2):  266-266.  doi:10.11947/j.AGCS.2017.20160533

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Theory and Technology Research on Celestial Navigation Based on the Sun

ZHAN Yinhu

2017, 46(2):  267-267.  doi:10.11947/j.AGCS.2017.20160542

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Study on Present-day Crustal Deformation in the Arc-Continent Collision Zone of Taiwan and Adjacent Area

WU Xiaolong

2017, 46(2):  268-268.  doi:10.11947/j.AGCS.2017.20160556

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