Table of Content

20 April 2017, Volume 46 Issue 4

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Establishment of High Precision DEM in Antarctic Dome A Area with Taking the Waveform Retracking,Slope Correction and the Data Fusion into Account

LI Fei, SONG Guoyun, YANG Yuande, HAO Weifeng, YANG Quanming

2017, 46(4):  403-410.  doi:10.11947/j.AGCS.2017.20160486

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This paper introduces three kinds of waveform retracking algorithm: OCOG, CFI and LIRT in the CryoSat-2 LRM mode. The accuracy of satellite data is evaluated by comparing the results of three waveform retracking algorithm, based on the measured GPS data in the Dome A area of Antarctica. The results show that the accuracy of the optimal OCOG waveform retracking algorithm is the best, the average difference between the results and GPS is about -0.07 m, the standard deviation is about 0.60 m, which is obviously better than the other two algorithms. By comparing the relationship between the slope and the precision of the satellite data, we find the influence of slope factors on the precision of the satellite altimetry data can't be ignored, the verification results show that the slope correction can improve the accuracy of satellite altimetry by about 38% in the Dome A area. Finally we establish the Antarctic Dome A region DEM by combining the GPS and CryoSat-2 data, which resolution is 300 m.the accuracy of fused DEM is about 0.24 m.

Kinematic Orbit Determination Method Optimization and Test Analysis for BDS Satellites with Short-arc Tracking Data

GUO Rui, CHEN Jinping, ZHU Lingfeng, TANG Guifen, WU Xiaoli

2017, 46(4):  411-420.  doi:10.11947/j.AGCS.2017.20160361

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Rapid orbit recovery is a puzzle for the BDS satellites after orbit maneuvers. Two kinematic orbit determination methods are studied, with two orbit determination models being established. The receiver system error and serious multipath error exist in the BDS system. The co-location method is proposed to estimate and calibrate the receiver system errors. A CNMC (code noise and multipath correction) method is introduced to weaken the multipath error. Therefore the data quality is controlled efficiently for the receivers in the short tracking arc. The GEO/IGSO/MEO real data is emploied to carry out tests and validation. Using 10 min short tracking arc, the kinematic precise orbit determination accuracy is about 3.27 m for the GEOs, and 8.19 m for the IGSOs, and 5.9 m for the MEOs. Rapid orbit determination is achieved, which satisfying the orbit requirements from the BDS RDSS services. The kinematic precise orbit determination method also supports the RDSS service walking up to the global world.

Performance Analysis of Different NeQuick Ionospheric Model Parameters

WANG Ningbo, YUAN Yunbin, LI Zishen, LI Min, HUO Xingliang

2017, 46(4):  421-429.  doi:10.11947/j.AGCS.2017.20160400

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Galileo adopts NeQuick model for single-frequency ionospheric delay corrections. For the standard operation of Galileo, NeQuick model is driven by the effective ionization level parameter Az instead of the solar activity level index, and the three broadcast ionospheric coefficients are determined by a second-polynomial through fitting the Az values estimated from globally distributed Galileo Sensor Stations (GSS). In this study, the processing strategies for the estimation of NeQuick ionospheric coefficients are discussed and the characteristics of the NeQuick coefficients are also analyzed. The accuracy of Global Position System (GPS) broadcast Klobuchar, original NeQuick2 and fitted NeQuickC as well as Galileo broadcast NeQuickG models is evaluated over the continental and oceanic regions, respectively, in comparison with the ionospheric total electron content (TEC) provided by global ionospheric maps (GIM), GPS test stations and JASON-2 altimeter. The results show that NeQuickG can mitigate ionospheric delay by 54.2%~65.8% on a global scale, and NeQuickC can correct for 71.1%~74.2% of the ionospheric delay. NeQuick2 performs at the same level with NeQuickG, which is a bit better than that of GPS broadcast Klobuchar model.

Crustal Subsidence Analysis from GNSS Data for Dagang Tidal Station in Qingdao

WU Fumei, WEI Ziqing, LIU Guangming

2017, 46(4):  430-435.  doi:10.11947/j.AGCS.2017.20160506

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Crustal subsidence at Dagang tidal station affects the Huanghai mean sea level which defines the national height datum. The crustal subsidence at Dagang tidal station located 1.5 km away from Qingdao GNSS fiducial station is analyzed, by using approximately 10 years of GNSS observations. Firstly, the daily relax solutions and daily constrained solutions for coordinates of this station are computed in a combined adjustment involving a global GNSS net of 50 IGS stations and a regional net of 43 CMONOC stations. Then, a time series spanning 10 years for station coordinates aligned to ITRF2014 is obtained. And next, the time series of height components is analyzed to detect outliers, offsets, trends and frequencies and the amplitudes of periodic parts and the values of offsets are obtained. It is shown that no trend is found in the series. But it is found that the annual and semi-annual signals influence the changes of the series obviously. Finally, it is concluded in combination with the analysis of tidal data for Dagang tidal station that the mean sea level at Dagang tidal station is ascending with a speed of 1.62 mm/a.

Accuracy Test of the Absolute Gravimeter FG5X-246

ZHAN Jingang, WANG Yong, BAI Lei, ZHANG Erlin, YAO Yixin

2017, 46(4):  436-441.  doi:10.11947/j.AGCS.2017.20160574

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The observation accuracy of the absolute gravimeter FG5X-246 is tested by using the weak force test platform. The disturbing gravity field, which is produced by changing the distance between the disturbing mass and the observation point,can be superposed on the background gravity field directly. It is measured that this gravity change using FG5X-246 absolute gravimeter and compared it with that of theoretical disturbing gravity field and then determined the accuracy of the absolute gravity observations. The test results show that when the height of the disturbing mass changes from 1.810 4 m to 1.409 9 m, the disturbing gravity field changes for 48.81 μGal (1 Gal=1 cm/s²), while FG5X-246 absolute gravimeter senses the gravity change of 48.0 μGal, and the difference between the measurement value and the theoretical value is 0.81 μGal. When the height changes from 1.810 4 m to 1.010 1 m, the disturbing gravity field changes for -15.44 μGal, while FG5X-246 absolute gravimeter senses the gravity change of -16.20 μGal, the difference of them is 0.76 μGal. When the height changes from 1.409 9 m to 1.010 1 m, the disturbing gravity field changes for-64.20 μGal, while FG5X-246 absolute gravimeter senses the gravity change of -64.25 μGal, the difference of them is 0.05 μGal.The results indicate that the FG5X-246 absolute gravimeter sensing external gravity change error is no more than 1 μGal, that is, the accuracy of the measured value is better than 1 μGal.

The Algorithm of Triple-frequency Ambiguity Resolution between BDS Network RTK Reference Stations

GAO Meng, XU Aigong, ZHU Huizhong, GE Maorong, YANG Qiushi

2017, 46(4):  442-452.  doi:10.11947/j.AGCS.2017.20160179

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BeiDou navigation satellite system is currently the only system which the whole constellation offers triple-frequency observation data, triple-frequency observation is conducive to carrier phase ambiguity fixing quickly and accurately. The algorithm of triple-frequency integer ambiguity resolution between BDS network RTK reference stations is proposed. The observation of B2 frequency and B3 frequency and the strict criterion of ambiguity fixing are used to determine extra-wide-lane integer ambiguity. The linear relationship between fixed extra-wide-lane integer ambiguity and other wide-lane integer ambiguity is selected as constraint conditions, then the wide-lane integer ambiguity, relative zenith tropospheric delay error and ionospheric delay error are estimated and the wide-lane integer ambiguity can be fixed by search mode. There is a kind of integer linear relationship between fixed wide-lane integer ambiguity and triple-frequency carrier phase integer ambiguity, this linear relationship is added to the observation model of carrier phase ambiguity parameter estimation and the integer ambiguity can be fixed. This algorithm is tested by the measured triple-frequency data of BDS CORS network. The results indicate that triple-frequency carrier phase ambiguity can be fixed accurately and effectively with the method.

Real-time Cycle-slip Detection and Repair Algorithm of GNSS Triple-frequency Observations

LIU Liu, LÜ Zhiwei, YU Xiaodong, WANG Pengxu, YANG Dongsen, ZHANG Lundong, CONG Dianwei

2017, 46(4):  453-459.  doi:10.11947/j.AGCS.2017.20160532

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Method of cycle-slip detection based on Geometry-free observation combinations has insensitive cycle-slip. This paper analyzes the principle of cycle-slip detection based on the geometric relationship. Then study the similarities and differences of more than one geometry free phase combinations separately. And study the effect of adding a MW(Melbourne Wübbena) combination. We proposed to select GF(Geometry Free) combinations by cross-sectional area. Finally BeiDou triple-frequency data have been used to validate the conclusion. We conclude that two geometry-free phase combination is the most reasonable choice for the detection of insensitive cycle-slip. And a MW combination can obviously decrease the amounts of insensitive cycle-slip. The optimized algorithm only has 1 insensitive cycle slip, and all detected cycle-slip repaired successfully.

Block Adjustment of Vehicle-borne Multi-camera Rig Images Using Extended Collinearity Equations

YIN Li, WANG Yidan

2017, 46(4):  460-467.  doi:10.11947/j.AGCS.2017.20160464

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This paper introduces the extended collinearity equations into aerial triangulation of the vehicle-borne multi-camera rig images to improve the positioning accuracy. The cameras in a multi-camera rig are rigidly fixed and the relative position and orientation parameters among the mono cameras of multi-camera rig can be calibrated accurately, so the extended collinearity equations can be used to extend the imaging unit from a mono camera image to multiple images of multi-camera rigs. Compared with the existing spherical models, including the spherical ideal model and the spherical rigorous model, the extended collinearity equations used in this paper avoid the spherical projection error and fusion error caused by the misalignment of projection centers. Experimental results show that the method omits the processing procedure of model projection and fusion of overlap areas, which avoids the precision loss and complicated processing procedure, and finally obtains more robustness triangulation net, more precise and robust position accuracy.

Perpendicular Impervious Index for Remote Sensing of Multiple Impervious Surface Extraction in Cities

TIAN Yugang, XU Yun, YANG Xiaonan

2017, 46(4):  468-477.  doi:10.11947/j.AGCS.2017.20160304

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Focusing on the issues of impervious layers' heterogeneity and confusion with soil, a method is presented—perpendicular impervious index (PⅡ), which considers blue and near infrared bands selected based on spectral characteristics of ground objects in LandSat-8 images. The PⅡ is established in a linear form, and its reference line is calculated based on the angle bisector of impervious layer line and soil line. Impervious surfaces are extracted using PⅡ on LandSat-8 images of Beijing and Wuhan, which is compared with the normalized difference building index (NDBI), ratio resident-area index (RRI) and biophysical composition index (BCI) in the same areas. The conclusions are as follow: ① PⅡ is superior than other indexes in separating impervious layers from bare soil in both the Wuhan and Beijing, the extracting accuracy is 96.05% and 96.76%,respectively; ② PⅡ is also effective in different environments, where the impervious layer shows various spectrums. Due to the linear combination form, PⅡ can adjust its coefficients depending on spectra of ground objects in different study areas, which gets higher accuracy in extracting impervious layers than other indexes,especially in regions containing more bare soil.

Spatial Scale Uncertainties on Quantitative Remote Sensing of Water Qualities

LI Jian, TIAN Liqiao, CHEN Xiaoling

2017, 46(4):  478-486.  doi:10.11947/j.AGCS.2017.20160296

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The rapid development of the Earth Observation (EO) technology offers substantial data for remote sensing monitoring of water environment, however, the research and applications are often impeded by inconsistent products from multi-resolution remote sensing dataset. A point-spread-function (PSF) based spatial resolution transformation approach was proposed, to mitigate scale errors from multi-platform sensors of varied spatial resolution. Using the high spatial resolution data of GF-1 (16 m) as reference, medium to low spatial resolution data were simulated, including Landsat-like and Terra/Aqua MODIS-like images. Comparisons between the PSF based scale transformation method and classical method revealed significant correlation, which also prove the efficiency of the proposed method. The scale errors of the remote sensing reflectance (RRS) average method are lower than the suspended practical matter (SPM) average method. Higher than 5% scale errors were produced by spatial scale transformation in high dynamic turbid waters, while for calm ocean waters, the error was less than 0.5%. Therefore, it is crucial for selection of proper scale transformation method, to achieve consistent remote sensing products from multi-source data.

Simulation Analysis of Cylindrical Panoramic Image Mosaic

ZHU Ningning

2017, 46(4):  487-497.  doi:10.11947/j.AGCS.2017.20160456

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With the rise of virtual reality (VR) technology, panoramic images are used more widely, which obtained by multi-camera stitching and take advantage of homography matrix and image transformation, however, this method will destroy the collinear condition, make it's difficult to 3D reconstruction and other work. This paper proposes a new method for cylindrical panoramic image mosaic, which set the number of mosaic camera, imaging focal length, imaging position and imaging attitude, simulate the mapping process of multi-camera and construct cylindrical imaging equation from 3D points to 2D image based on photogrammetric collinearity equations. This cylindrical imaging equation can not only be used for panoramic stitching, but also be used for precision analysis, test results show: ①this method can be used for panoramic stitching under the condition of multi-camera and incline imaging; ②the accuracy of panoramic stitching is affected by 3 kinds of parameter errors including focus, displacement and rotation angle, in which focus error can be corrected by image resampling, displacement error is closely related to object distance and rotation angle error is affected mainly by the number of cameras.

A Line Simplification Algorithm Considering Spatial Relations between Two Lines

LI Chengming, GUO Peipei, YIN Yong, WU Pengda, GU Teng

2017, 46(4):  498-506.  doi:10.11947/j.AGCS.2017.20160546

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Line element simplification has always been a hot research topic in the field of cartography generalization and expression. However, more existing line simplification algorithms aimed at single line rather than spatial relationship between linear elements. At the same time, there are some problems with classical algorithm, such as blunt performance(D-P algorithm), missing local extreme point and curve intersection(L-O algorithm). So, this paper puts forward a line simplification algorithm taking account of spatial relations between two lines. Line global simplification method(LGSM), vector displacement, area displacement and so on are proposed. Experiments are carried out on three kinds of line elements,such as contour lines, rivers and roads. The experiments' results show that the proposed algorithm can maintain the overall shape of the curve better and reduce the complexity of the curve effectively, the shape is more smooth and has a high position accuracy.

Renewal of Road Networks Using Map-matching Technique of Trajectories

WU Tao, XIANG Longgang, GONG Jianya

2017, 46(4):  507-515.  doi:10.11947/j.AGCS.2017.20150479

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The road network with complete and accurate information, as one of the key foundations of Smart City, bears significance in fields like urban planning, traffic managing and public traveling, et al. However, long manufacturing period of road network data, based on traditional surveying methods, often leaves it in an inconsistent state with the latest situation. Recently, positioning techniques ubiquitously used in mobile devices has been gradually coming into focus for domestic and overseas scholars. Currently, most of approaches, generating or updating road networks from mobile location information, are to compute with GPS trajectory data directly by various algorithms, which lead to expensive consumption of computational resources in case of mass GPS data covering large-scale areas. For this reason, we propose a spiral update strategy of road network data based on map-matching technology, which follows a “identify→analyze→extract→update” process. The main idea is to detect condemned road segments of existing road network data with the help of HMM for each trajectory input, as well as repair them, on the local scale, by extracting new road information from trajectory data.The proposed approach avoids computing on the entire dataset of trajectory data for road segments. Instead, it updates information of existing road network data by means of focalizing on the minimum range of potential condemned segments. We evaluated the performance of our proposals using GPS traces collected on taxies and OpenStreetMap(OSM) road networks covering urban areas of Wuhan City.

Fast Search the Density Peaks and Clustering Method for Check-in Data

LIU Meng, WU Qunyong, QIU Duansheng, SUN Mei, ZHANG Qiang

2017, 46(4):  516-525.  doi:10.11947/j.AGCS.2017.20160377

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Check-in data obtained from Location-based Social Network (LBSN) is a sort of crowd geographic data which will reveal daily activities of urban residents. Different check-in behaviors with the same check-in location will produce the phenomenon of location duplication because of location candidate function in LBSN system. The current density-based spatial clustering algorithms have the following problems: ①difficulty to find density peak point. ②clustering error caused by check-in point objects with duplicate positions. In order to solve these problems, we proposed a fast search density peaks and clustering method for check-in data, based on clustering by fast search and find of density peaks (CFSFDP). Firstly, position repetition frequency was introduced and calculated to illustrate the number of the check-in position duplications data. Secondly, a new type of point feature was constructed by adding position repetition frequency of the original check-in position data, which was used as study object to search density peaks. At last, clustering algorithm based on density peak point was constructed in which density connectivity was taken into account to ensure the continuity and integrity of density clusters. Taking check-in data obtained from Sina Microblog as an example, an experiment was designed and implemented. The results demonstrates:①Clustering method can effectively avoid the problem that the outlier location object with high repeatability is chosen as the peak and clustering, and has excellent spatial adaptability as well when comparing with check-in data from other area. ②Extracted density peak points can not only be used to represent the center of the hot zone, but also reflect the concentration trend of the hot zone, which can help to explore the dynamic change of the hot zone.

Method of Deformation Probability Prediction Considering the Influence of Uncertainty Factors

WEI Guanjun, DANG Yamin, ZHANG Chuanyin, YANG Weifang

2017, 46(4):  526-532.  doi:10.11947/j.AGCS.2017.20160531

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A probabilistic prediction method of deformation is proposed based on the MCMC algorithm and the Bayesian Prediction Theory.This method describes the uncertainty of deformation prediction using probability distributions and implement the recursive process of prediction by probability rules. The settlement data from the Nanjing-Hangzhou high-speed roadbed is used to quantitatively analyze the forecast values, reliability intervals and so on, and then the results are compared with those obtained by the least squares estimation and the immune algorithm, and it has shown that the proposed method is effective and feasible.

Key Technologies of GNSS Time Scale

WU Yiwei

2017, 46(4):  533-533.  doi:10.11947/j.AGCS.2017.20160660

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A Procedural Modeling Method with Hierarchical Spatial Constraints for Generating High-Speed Railway Scenes

ZHANG Heng

2017, 46(4):  534-534.  doi:10.11947/j.AGCS.2017.20160638

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Estimation of the Background Noise Levels and Extraction of Signals at SG Stations

ZHANG Miaomiao

2017, 46(4):  535-535.  doi:10.11947/j.AGCS.2017.20160642

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Researches on Theory and Method of GNSS Monitor and Assessment

ZHANG Qinghua

2017, 46(4):  536-536.  doi:10.11947/j.AGCS.2017.20160676

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