Table of Content

20 February 2015, Volume 44 Issue 2

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Using Allan Variance to Analyze the Zero-differenced Stochastic Model Characteristics of GPS

ZHANG Xiaohong, ZHU Feng, XUE Xueming, TANG Long

2015, 44(2):  119-127.  doi:10.11947/j.AGCS.2015.20130513

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The estimation criteria for solving parameters in zero-differenced GPS positioning is that observations obey Gaussian white noise distribution. But a number of pioneering studies point out that the white noise would be damaged by satellites errors, propagation errors, station environment errors and so on. Meanwhile, un-modeling errors also have adverse effects. These errors not only undermine the assumption estimation criteria, and some non-white noises are likely to be absorbed by state parameters. In result, the accuracy of estimates is influenced. This paper regards white noise, colored noise and un-modeling errors as ZD stochastic model of GPS. Then the Allan variance method is proposed to analyze the posteriori residuals which can represent the Stochastic characteristics of GPS data. Noise component and parameters are mainly investigated. The result shows GPS noise behaves as WN plus GM. The phase and pseudorange WN is 2.392 mm and 0.936 m respectively, GM process noise is 4.450 mm/√s and 0.833 m/√s respectively, correlation time is 52.074 s and 14.737 s respectively. It is found that the phase GM component is associated with satellite, but the rest is associated with station. A number of analysis indicate that the ZD stochastic model characteristics of GPS obeys non-Gaussian white noise distribution and is to be refined.

Ambiguity Resolution for GPS/GNSS Network Solution Implemented in SPODS

RUAN Rengui

2015, 44(2):  128-134.  doi:10.11947/j.AGCS.2015.20130461

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Ambiguity resolution plays an essential role in global GPS/GNSS network solution. In order to fix as many double-difference(DD) ambiguities to the nearest integers as possible, a set of "most-easy-to-fix" independent DD-ambiguities has to be defined. The most usable state-of-art method (the "traditional" method)at present is to make the independency checking on two levels firstly on the baseline level and then the network level, in which the DD-ambiguity candidates are sorted by their fixing probabilities on both levels. Considering the fact that, in general global network solution, the number of stations involved is usual times larger than that of satellites, a new approach for independent DD-ambiguities selection was presented, which makes the independency checking in an analogous two-level way firstly on the constellation level and then the network level. Together with a new procedure for sequential ambiguity fixing base on updating the upper triangular square root of covariance matrix, the new approach is implemented in the satellite positioning and orbit determination system (SPODS) software which is designed and developed at Xi'an Research Institute of Surveying & Mapping. Validation experiment with GPS observation data collected from about 64 IGS stations was carried out, which demonstrate that 1D RMSs for daily orbit solution, compared with IGS final combined solution, are about 0.012 m, and about 92% of DD-ambiguities were fixed, with only neglectable tiny difference for both the new and traditional method. Another experiment with varied number of stations indicates that the ratio of the number of DD-ambiguities candidates to be checked for independency on the network level between the new and the traditional approach is nearly equal to the ratio of satellites to stations involved. For the cases that more stations are involved than satellites, which are common in actual GPS/GNSS network solution, the computation time for independent DD-ambiguities selection is reduced with the new approach, the more stations involved, the greater advantage is exhibited.

Adjustment Criterion and Algorithm in Adjustment Model with Uncertain

SONG Yingchun, XIE Xuemei, CHEN Xiaoling

2015, 44(2):  135-141.  doi:10.11947/j.AGCS.2015.20130213

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Uncertainty often exists in the process of obtaining measurement data, which affects the reliability of parameter estimation. This paper establishes a new adjustment model in which uncertainty is incorporated into the function model as a parameter. A new adjustment criterion and its iterative algorithm are given based on uncertainty propagation law in the residual error, in which the maximum possible uncertainty is minimized. This paper also analyzes, with examples, the different adjustment criteria and features of optimal solutions about the least-squares adjustment, the uncertainty adjustment and total least-squares adjustment. Existing error theory is extended with new observational data processing method about uncertainty.

Analysis of Various Approaches for Gravity Field Recovery by Using the GOCE Satellite Orbits

SU Yong, FAN Dongming, YOU Wei

2015, 44(2):  142-149.  doi:10.11947/j.AGCS.2015.20130412

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The energy conservation approach has been adopted to exploit GOCE orbit information in earlier GOCE time-wise and space-wise gravity field models which are two kinds of official ESA products, but the accuracy of long-wavelength gravity signal is low. Gravity field recovery with GOCE satellite data is an ill-posed problem and the precision of zonal coefficients is low due to the polar gaps, which needs be processed by regularization technique. This paper analyzes the accuracy of existing approaches for gravity field recovery in processing GOCE data and the selection of optimal regularization techniques and parameters. Several gravity field models were recovered based on GOCE precise orbits of 92-days from 2009-11-01 to 2010-01-31 with the energy conservation approach, short-arc integral approach and average acceleration approach. These approaches do not require any initial values of unknown parameters and reference gravity models. Besides, the Tikhonov regularization technique was applied to tackle the ill-posed problem. The results show that the highest accuracy of the model is recovered by the average acceleration approach, the lowest accuracy is the energy conservation approach, and the accuracy of short-arc integral approach is slightly worse than average acceleration approach. Therefore, such methods as the average acceleration approach or short-arc integral approach should be recommended to be applied when processing the GOCE orbit data. Gravity field models can effectively recovered by GOCE orbit data with the order and degree 120 when orbit and gradiometer data are combined to processes in the future. Kaula regularization and second-order Tikhonov (SOT) are superior to other regularization techniques in dealing with ill-posed problem of GOCE, and the corresponding optimal regularization parameters of both techniques are consistent. However, the effects of polar gaps could not be completely inhibited by regularization technique; it should be combined with other data, such as GRACE satellite data, to get the desired results.

Estimation of GLONASS Code Inter-frequency Biases with Multiple Parameters Based on a Single Station and Its Impact on Combined Precise Point Positioning

LIU Zhiqiang, WANG Jiexian, DUAN Bingbing

2015, 44(2):  150-159.  doi:10.11947/j.AGCS.2015.20130800

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The disadvantages of ignoring GLONASS receiver code inter-frequency biases(IFBs) in GPS/GLONASS combined precise point positioning (PPP) are analysed in this contribution. A new algorithm of combined PPP and code IFBs estimation based on "multiple parameters" is proposed where inter-system bias parameter is merged with code IFB. Multiple independent inter-system and inter-frequency bias (ISFB) parameters are introduced to the observation equations which could compensate the GLONASS code IFBs in the function model. In the meantime, the GLONASS code IFBs can be estimated precisely based on a single station. GPS/GLONASS observation data from 30 IGS sites which involves 6 different GNSS receiver manufacturers is processed with the proposed algorithm. The results show that the GLONASS code IFBs could be several meters and a significant correlation exists between code IFB and signal frequency. It seems to be difficult to provide a priori code IFB precisely with simple function model. GLONASS code IFBs with the same receiver manufacturer mostly show similar characteristics, however, abnormal behaviors are also found in some receivers. It is worth to note that GLONASS code IFBs could be quite different with two receivers even if their receiver types, firmware versions and antenna types are all the same. The PPP results demonstrate that the new algorithm can significantly accelerate the convergence of combined PPP by compensating the GLONASS code IFBs efficiently. The combined PPP accuracy of "multiple parameters" method is comparable with that of traditional "single parameter" method and almost unaffected by freedom reduction of the function model.

Chinese Continental Water Storage and Ocean Water Mass Variations Analysis in Recent Ten Years Based on GEACE RL05 Data

LU Fei, YOU Wei, FAN Dongming, HUANG Qiang

2015, 44(2):  160-167.  doi:10.11947/j.AGCS.2015.20130753

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Chinese mainland water reserves and the variation tendency of the ocean water mass from 2003 to 2012 are recovered with the data of GRACE RL05 provided by Center for Space Research. An improved de-correlated filtering algorithm is presented. which sets the highest order coefficient to be fitted up to 55 and the border coefficient can also be directly fitted without being used as center of the sliding window. The algorithm is proposed with significant decrease in stripes compared with traditional algorithms. The results show that the area, where terrestrial water changes a lot, are the north China plain, the three gorges region, the border region of Qinghai, Xinjiang and Tibet respectively. During the recent ten years, the groundwater of north China plain reduces at the rate of 4.1±1.3 mm/a, The change of ground water and surface water are mainly between 2004 and 2008. GRACE can detect the prominent of mass change of the Three Gorges Reservoir in the form of equivalent water height, which are 52 mm、18 mm and 7 mm respectively. The ground water and terrestrial water in the border region of Qinghai, Xinjiang and Tibet have increased at the rate of 10.6±0.9 mm/a、11.6±1.1 mm/a respectively. The results of GRACE data show that the ocean mass rise trend of East China Sea, South China Sea and Yellow China Sea are 4.23±0.9 mm/a、1.33±0.9 mm/a、3.09±1.1 mm/a, respectively after the deduction of the glacial isostatic adjustment. The ocean water mass of East China Sea rises significantly faster than the other two areas.

On the Effect of Linearization and Approximation of Nonlinear Baseline Length Constraint for Ambiguity Resolution

NIE Zhixi, WANG Zhenjie, OU Jikun, JI Shengyue

2015, 44(2):  168-173.  doi:10.11947/j.AGCS.2015.20130491

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Additional nonlinear baseline length constraint is often used for GNSS dynamic relative positioning, but the LAMBDA method can only deal with linear constraint model. So, it is necessary to linearize and approximate nonlinear constraint conditions. Linearized approximate constraint usually increases the success rate of fixing integer ambiguity, but for the ultra-short baseline, the opposite results may be derived. When will the linearized approximate baseline length constraint can improve the success rate of fixing ambiguity? This article attempts to answer these questions. Firstly, the float solution's maximum influence value formula is derived when using linearized approximate baseline length constraint, based on GNSS relative positioning model; Secondly, a discriminant condition is given to determine whether baseline length constraint can be linear approximation. When the condition is met, the influence can be ignored, linearized approximate baseline length constraint can improve the accuracy of float solution and increase the success rate of fixing ambiguity,on the contrast, the influence may not be ignored, linear approximation will result in a biased float solution and the ambiguity cannot be fixed correctly; At last, the foregoing conclusions are verified with some numerical example in this paper.

The Inversion of Terrestrial Water Storage Changes by Non-isotropic Combination Filter

CHAO Nengfang, WANG Zhengtao, SUN Jian

2015, 44(2):  174-182.  doi:10.11947/j.AGCS.2015.20130719

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The inversion of variations of terrestrial water storage by the earth time-variable gravity filed model makes a great contribution to global climate change, however, the spherical harmonics of time-variable gravity field have correlation problem and significant errors in high orders and degrees, and so optimal filtering method is needed to solve this problem. In this article, a new filter was devised named‘non-isotropic combination filter’, and showed a better performance. The basic idea of the new filter is to apply the Gaussian filter and the RMS filter to low-degree and high-degree harmonic coefficients separately. In this paper, we first analyze the error characteristics of the latest GRACE RL05 series variable gravity field model, compare the validity and precision with Gaussian filter, improved Gaussian filter, RMS filter, DDK filter, the non-isotropic combination filter and verified them with the model. It shows that the mean square error of the non-isotropic combination filter and model is the least. Based on above analysis, we find that the non-isotropic combination filter can suppress the noises in high-degrees and high-orders, eliminate the N-S striping errors, lower signal leakage errors, improve the ratio of signal-to-noise more effectively compared with the previous filters.

Global Optimization and Whole Registration Algorithm of Multi-view 3D Laser Point Cloud

LI Cailin, GUO Baoyun, JI Zheng

2015, 44(2):  183-189.  doi:10.11947/j.AGCS.2015.20130737

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A global optimization and whole registration algorithm of multi-view 3D laser point cloud is presented. Detailed derivation of global optimization adjustment model of multi-view laser point cloud is showed in this paper. This algorithm can handle disordered and scattered multi-view 3D laser point cloud, at the same time optimal transformation parameters can be obtained. Practical 3D laser point cloud data are exemplified for the feasibility and effectiveness of proposed methods.

A Whitening Transformation Based Approach to One-class Classification of Remote Sensing Imagery

BO Shukui, LI Xiang, LI Lingling

2015, 44(2):  190-197.  doi:10.11947/j.AGCS.2015.20130439

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In this study, a whitening transformation based approach to one-class classification of remote sensing imagery is investigated. Only positive data are required to train the one-class classifier. Firstly, the image data is mapped to a new feature space using the whitening processing with all directions of the class of interest. Then a threshold is selected to make a binary prediction. A heuristic method of threshold selection is performed in the experiment of one-class classification. A series of values are set to the threshold based on standard deviation, and perform the one-class classification with each threshold value. The experiment shows that high accuracy is achieved with the threshold range from 3 to 4 standard deviations of the mean. Finally, the results of one-class classification with the threshold of 3 standard deviations are compared to that of one-class support vector machine. The results indicate that the proposed method provides nearly the same accuracy of one-class classification as one-class support vector machine. The advantage of the proposed method is that it can use a constant threshold to extract various land types.

A Methodology of Image Segmentation for High Resolution Remote Sensing Image Based on Visual System and Markov Random Field

XU Miaozhong, CONG Ming, WAN Lijuan, XIE Tianpeng, ZHU Xiaoling

2015, 44(2):  198-205.  doi:10.11947/j.AGCS.2015.20130453

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In consideration of the visual system's tremendous ability to perceive and identify the information, a new image segmentation method is presented which simulates the mechanism of visual system for the high resolution remote sensing image segmentation with Markov random field model. Firstly, the characteristics of the visual system have been summarized as: hierarchy, learning ability, feature detection capability and sparse coding property. Secondly, the working mechanism of visual system is simulated by wavelet transform, unsupervised clustering algorithm, feature analysis and Laplace distribution. Then, the segmentation is achieved by the visual mechanism and the Markov random field. Different satellites remote sensing images are adopted as the experimental data, and the segmentation results demonstrate the proposed method have good performance in high resolution remote sensing images.

Buildings Extraction from Polarimetric SAR Image Using Improved Three-component Decomposition and Wishart Classification

LIU Xiuguo, JIANG Ping, CHEN Qihao, CHEN Qi

2015, 44(2):  206-213.  doi:10.11947/j.AGCS.2015.20130535

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To address the misclassification issue on buildings extraction based on Freeman decomposition method, a novel improved three-component decomposition model is proposed in this paper. By combining the selective de-orientation derived from the circular polarization correlation coefficient method with the generalized volume scattering model, it can accurately characterize the scattering characteristics of surface features. On this basis, the complex Wishart iterative classification is introduced to develop a new method of buildings extraction. An E-SAR L band polarimetric SAR image was used to verify the effectiveness of this modified algorithm. The experiment result shows it could perform better in distinguishing between oblique buildings and forest, and consequently improve the accuracy of buildings extraction.

A Fast Endmember Extraction Algorithm Using Spectrum Gradient Features

TIAN Yugang, YANG Gui

2015, 44(2):  214-219.  doi:10.11947/j.AGCS.2015.20130392

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Due to the large amount of image data, most algorithms for endmember extraction cost huge time, which limits the wide application of them. A fast endmember extraction algorithm is proposed by using Spectrum Gradient Features as the searching rule. The core idea is composed of two parts, namely, rapid screening of candidate endmembers based on Spectral Gradient Features and endmember identification based on spectrum unmixing residual. Being able to quickly screen out a small amount of pixels from the image as candidate endmembers, the algorithm has excellent computational performance. This algorithm can also avoid non-endmember spectrum participating in endmember identification and can obtain a result of higher accuracy. The experimental result shows that this new algorithm can greatly improve the endmember extraction speed and recognize endmembers more accurately compared with IEA and ECHO. What's more, existing algorithms for endmember extraction can be applied better based on the principle of this algorithm, and the extraction speed can be improved remarkably.

A Visualization Method for Personal Geotagged Data

HUA Yixin, LI Xiang, WANG Lina, ZHANG Jin

2015, 44(2):  220-227.  doi:10.11947/j.AGCS.2015.20130808

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Geotagged personal datas, which are released by laptop, tablet PC or mobile device,contain personal data such as text, photos, video information and geographic position information. In this paper, we propose a new visualization method—the topological map of personal geotagged data (simply, the topological map) and provide the design and implementation of the core algorithm for the method. In order to evaluate the effectiveness of the method, we conduct a usability test for "a text list", "a thematic map" and "a topological map" and use analysis of variance(ANOVA) to deal with test data. The results show that the three kinds of user interfaces have statistically significant difference in terms of efficiency in finding personal geotagged data, and there are not significant difference between a text list and a topological map, while the latter is slightly faster than the former, however, both are significantly better than a thematic map.

A Real-time Generalization and Multi-scale Visualization Method for POI Data in Volunteered Geographic Information

YANG Min, AI Tinghua, LU Wei, CHENG Xiaoqiang, ZHOU Qi

2015, 44(2):  228-234.  doi:10.11947/j.AGCS.2015.20130564

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With the development of mobile and Web technologies, there has been an increasing number of map-based mushups which display different kinds of POI data in volunteered geographic information. Due to the lack of suitable mechanisms for multi-scale visualization, the display of the POI data often result in the icon clustering problem with icons touching and overlapping each other. This paper introduces a multi-scale visualization method for urban facility POI data by combing the classic methods of generalization and on-line environment. Firstly, we organize the POI data into hierarchical structure by preprocessing in the server-side; the POI features then will be obtained based on the display scale in the client-side and the displacement operation will be executed to resolve the local icon conflicts. Experiments show that this approach can not only achieve the requirements of real-time online, but also can get better multi-scale representation of POI data.

Study on Relative Radiometric Correction and Digital Baseline-height Ratio Model for Stereo Mapping

DUAN Yini

2015, 44(2):  235-235.  doi:10.11947/j.AGCS.2015.20140373

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Study on Processing, Forward Modeling and Inversion Algorithms of Satellite Magnetic Anomaly Data in Spherical Coordinate System

DU Jinsong

2015, 44(2):  236-236.  doi:10.11947/j.AGCS.2015.20140471

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