Acta Geodaetica et Cartographica Sinica

Analysis of Mutual Shielding Effect Between the 25 m and 13 m Radio Telescope at Sheshan

LI Jinling, WEN Bo, SUN Zhongmiao, FAN Qingyuan, HE Gengxin, HUANG Fei, LIU Cong

2018, 47(1): 1-7. doi:10.11947/j.AGCS.2018.20160670

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In accordance with practical needs of a project,the mutual shielding effect between two radio antennas located within some limited area is analyzed in this paper.The concept of the externally connected sphere of an antenna in altazimuth(azimuth-elevation) mount is put forward.A calculation method via numerical integral of the area of a part of spherical crown is given.The mutual shielding effect between the 25 m and 13 m radio telescope at Sheshan is analyzed and estimated.The result is of theoretical reference meanings in the design phase of the project concerning the position selection and height design of the supporting tower of the 13 m antenna.The analytical idea and method can also be used as reference by similar engineering practice.

Snow Depth Detection and Error Analysis Derived from SNR of GPS and BDS

WANG Zemin, LIU Zhikang, AN Jiachun, LIN Guobiao

2018, 47(1): 8-16. doi:10.11947/j.AGCS.2018.20160644

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There are several significant advantages in snow depth inversion with GNSS reflected signals,such as all-time,all-weather,large amount of data and low cost.An experiment of GNSS-reflectometry was designed at Arctic Yellow River Station and dual-frequency signal to noise ratio (SNR) observations of GPS and BDS were collected.The effects on snow depth inversion,including satellite elevation,arc length,number of satellites,azimuth,time scale,constellation structure,signal frequency and SNR intensity,were discussed comprehensively.And then the inversion accuracy and reliability were improved by large sample statistics,quality control and error analysis.According to the error analysis,we recommend the following inversion strategy:to use L1 and B1I observations,with 5 to 25 degrees satellite elevation,from multi-satellites and four azimuths.In this way,we can finally achieve the accuracy of 5 cm in one day.In addition,arc length,constellation structure and signal frequency have small effects on the accuracy of the results.

A Modified SEVB Integer Ambiguity Search Algorithm

LIU Wanke, MA Liye, LU Liguo, LI Jianlong

2018, 47(1): 17-24. doi:10.11947/j.AGCS.2018.20170227

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A modified integer ambiguity search algorithm named MSEVB is proposed to overcome the disadvantage that SEVB algorithm is time-consuming under low float ambiguity precision.The proposed algorithm,by restricting initial search space and optimizing the calculation procedure,can effectively reduce the number of ambiguity candidates and redundant computation,so that the search efficiency is improved significantly.The experiment results indicate that MSEVB algorithm has significant improvement in search efficiency,compared with SEVB algorithm,when the precision of ambiguity resolution is low.Moreover,MSEVB algorithm is more insensitive to ambiguity dimension and precision,thus it has better performance in stability.

A Method for Dealing with the Systematic Errors of Partial EIV Semi-parametric Model

WANG Leyang, XIONG Luyun

2018, 47(1): 25-34. doi:10.11947/j.AGCS.2018.20160613

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The estimated values are affected so that they are not reliable if the observations contain systematic errors under the solution of total least squares.Thus the bad effect on the estimated values should be weakened so the relatively reliable solution can be obtained.This paper adds non parametric part (systematic errors) in the partial errors-in-variables (Partial EIV) model,building Partial EIV semi-parametric model.The penalized least square criterion is introduced to derive formula,and choose the proper regularization matrix in the experiments.The smoothing factor is acquired by the method of L-curve.The results of experiments show that the algorithm of Partial EIV semi-parametric model can mitigate systematic errors to a certain extent and obtain the more reliable solution than the traditional method.So the validity of the algorithm is verified.

An Improved Algorithm of Tendency Surface Filtering in Multi-beam Bathymetric Data Considering the Natural Neighboring Points Influence Field

ZHANG Zhiheng, PENG Rencan, HUANG Wenqian, DONG Jian, LIU Guohui

2018, 47(1): 35-47. doi:10.11947/j.AGCS.2018.20160565

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Aiming at the problems of uncertain fitting function,incomplete filtering effects and some soundings unreasonable exclusion by applying tendency surface filtering algorithm in multi-beam bathymetric data,the paper brought forward the concept of natural neighboring points influence field,which means the minimum local area of an arbitrary point in scattered soundings,and erects an improved algorithm of tendency surface filtering based on natural neighboring points influence field. Firstly,the paper analyzed the local approximate surface of the natural neighboring points influence field,and constructed the unified surface fitting function in the specific local coordinate system for natural neighboring points influence field. Secondly,by using the unified surface fitting function,the iterative tendency surface filtering method has been erected to filter gross error data affecting the judgment of the normal points step by step. At last,according to the different continuity of the boundary point on the mutation terrain within the neighborhood adjacent terrain,a judgment criterion to the boundary point is established to reserve the boundary point. Some experiments were completed to prove the validity of the algorithm. The experiments show that the improved algorithm can adapt to the submarine topographies of varied complexities,eliminate the gross error points in the multi-beam bathymetric data and preserve the normal and special points of actual submarine topography. Therefore,the precision of submarine topography expression is significantly improved.

The Analysis of Precise Point Positioning of BeiDou Navigation Satellite System Application in Crustal Motion Monitoring

WANG Yuebing, GAN Weijun, CHEN Weitao, LIAN Weiping, YOU Xinzhao

2018, 47(1): 48-56. doi:10.11947/j.AGCS.2018.20170147

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Based on more than two years BDS/GPS data observed by seven stations,we used precise point positioning (PPP) model of the PANDA software developed by Wuhan University,analyzed the positioning accuracy of single system and discussed the ability of BDS in crustal motion monitoring.The results showed that the BDS positioning accuracy in the horizontal direction was about 17 mm and the vertical direction was about 40 mm.The GPS positioning accuracy in the horizontal direction was better than 10 mm and the vertical direction was about 14 mm.The results of baseline statistics showed that BDS had lower ability to detect weak signals than GPS system,but it was still able to accurately reflect the characteristics of baseline length and rate between two sites.Comparing the velocity fields obtained from BDS and GPS,the results showed that the difference of the two sets of velocity field in horizontal directions was 1~2 mm/a,and there was no systematic difference.Although BDS PPP accuracy was lower than GPS,but it could still be used to monitor the crustal motion of the large deformation area.

A AMART Algorithm Applied to Ionospheric Electron Reconstruction

ZHAO Haishan, YANG Li, ZHOU Yanglin, DONG Ming

2018, 47(1): 57-63. doi:10.11947/j.AGCS.2018.20160540

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Aiming at the problem that the traditional MART algorithm has low iteration accuracy,a new tomographic inversion algorithm is proposed. On the one hand,The new algorithm takes into account the integration of the intercept of ray traversing pixels and electron density and distributes the iterative difference in a more reasonably. On the other hand,an adaptive relaxation factor related to the electron density is proposed to overcome the influence of propagation noise on electron density inversion. The GIM data and GPS dual frequency observation data are used to verify the feasibility and superiority of the new method iteration accuracy from two aspects of single ray iteration and multi ray iteration. The experimental results show that compared with the traditional MART algorithm,the electron density profile obtained by the new method is closer with those from ionosonde measurements.

One Step Solution to the Local Tie Vectors of GNSS/SLR in ITRF

MA Xiaping

2018, 47(1): 64-70. doi:10.11947/j.AGCS.2018.20170066

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This paper proposes a one-step solution of local tie vectors,the solution takes RP (Reference Point) and axes offsets of SLR telescope as unknown parameters,GNSS baselines network and conventional terrestrial observation (horizontal,vertical angle and distance) are combined in ITRF (International Terrestrial Reference Frame),and multiply constraint conditions are established between RP and observation marks and two axes offsets.Local tie vectors and related covariance matrices of the 3 co-located sites in Beijing,Kunming,Xi'an of CMONOC (Crustal Movement Observation Network of China) are solved with the proposed one step solution.The results show that the RMS (root mean square error) of local tie vectors is less than 2.0 mm.Besides,the differences are less than 2.0 mm compared with the traditional step by step solution,and the offsets and corresponding RMS between the horizontal axis and vertical axis are 3.8 mm,0.7 mm,3.6 mm and 1.3 mm,1.2 mm,1.3 mm,respectively.

Multimodal Image Registration Algorithm Considering Grayscale and Gradient Information

YAN Li, WANG Ziqi, YE Zhiyun

2018, 47(1): 71-81. doi:10.11947/j.AGCS.2018.20170368

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Multimodal image registration method based on feature matching can't satisfy the demands of pixel level registration precision.This paper proposes a multimodal image registration algorithm considering grayscale and gradient information.The nonparametric registration model based on Markov random field (MRF) makes full use of the image information of multimodal image to measure the similarity which considers the grayscale and the gradient statistical information are considered,and the value space is discretized to improve the convergence speed.The algorithm is validated both qualitatively and quantitatively demonstrating its potentials on three groups of multimodal image registration experiments.The result indicates that the proposed algorithm is superior to the polynomial model registration based on manual selection and the multimodal image registration only with gray information only.At the same time,this algorithm has some applicability for multimodal image registration of large deformation.In terms of spatial accuracy,the average registration error is less than 1 pixel and the maximum registration error is less than 2 pixels.

Panchromatic and Multi-spectral Fusion Method Combined with Adaptive Gaussian Filter and SFIM Model

WANG Mi, HE Luxiao, CHENG Yufeng, CHANG Xueli

2018, 47(1): 82-90. doi:10.11947/j.AGCS.2018.20170421

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Panchromatic and multi-spectral fusion technology can increase feature discriminant ability of remote sensing images.However,the abilities of fusing spatial information and keeping spectral information are conflict,and are hard to be balanced by common algorithms.SFIM (smoothing filter-based intensity modulation) can keep spectral information effectively,but is difficult to fuse spatial information which will reduces the holistic effect.Pointing to this problem,this paper analyzes the principles and characters of SFIM model,and proposes a fusion method combined with adaptive Gaussian filter and SFIM model (AGSFIM).Computing optimal parameter of Gaussian filter based on entirety mean-value-adjusted average gradient of multi-spectral bands,and adjusting down-sampled panchromatic image to same sharpness level which can confirm the balances of spatial information fusing ability and spectral information keeping ability.Beijing-2 and ZY-3 02 data are applied to test and six different fusion methods are used to compare.The experiments show that AGSFIM can effectively overcome SFIM's shortage and increase fusion images' spatial information.

Tie Point Extraction for SAR Images with Same Side-looking Direction from Different Trajectories Based on Differential Constraints

JIN Guowang, XIONG Xin, ZHANG Hongmin, XU Qing, LIU Hui, WANG Xintian

2018, 47(1): 91-101. doi:10.11947/j.AGCS.2018.20170129

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In order to extract tie points for SAR image block adjustment automatically and steadily,a method of tie point extraction based on differential constraints for SAR images with same side-looking direction from different trajectories is presented.It is aiming at SAR images with same side-looking direction and approximately parallel tracks,whose relative geometric distortion is small in azimuth and large in range.Firstly,image pyramids are built for two SAR images,and then these images are matched with correlation coefficient calculated by rectangular window with increased azimuth side from the top layer to the bottom layer.Mismatched points are removed by RANSAC algorithm with differential constraints.Coordinates for points in lower pyramid images are estimated with global bilinear transformation model in azimuth and local bilinear transformation model in range.Experiments performed on Envisat ASAR images and Chinese airborne SAR images validated the proposed method.

Combining the Pixel-based and Object-based Methods for Building Change Detection Using High-resolution Remote Sensing Images

ZHANG Zhiqiang, ZHANG Xinchang, XIN Qinchuan, YANG Xiaoling

2018, 47(1): 102-112. doi:10.11947/j.AGCS.2018.20170483

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Timely and accurate change detection of buildings provides important information for urban planning and management.Accompanying with the rapid development of satellite remote sensing technology,detecting building changes from high-resolution remote sensing images have received wide attention.Given that pixel-based methods of change detection often lead to low accuracy while object-based methods are complicated for uses,this research proposes a method that combines pixel-based and object-based methods for detecting building changes from high-resolution remote sensing images.First,based on the multiple features extracted from the high-resolution images,a random forest classifier is applied to detect changed building at the pixel level.Then,a segmentation method is applied to segement the post-phase remote sensing image and to get post-phase image objects.Finally,both changed building at the pixel level and post-phase image objects are fused to recognize the changed building objects.Multi-temporal QuickBird images are used as experiment data for building change detection with high-resolution remote sensing images,the results indicate that the proposed method could reduce the influence of environmental difference,such as light intensity and view angle,on building change detection,and effectively improve the accuracies of building change detection.

DEM Assisted Shadow Detection and Topography Correction of Satellite Remote Sensing Images in Mountainous Area

YUE Zhaoxi, ZHANG Yongjun, DUAN Yansong, YU Lei

2018, 47(1): 113-122. doi:10.11947/j.AGCS.2018.20170194

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A shadow detection and topography correction method based on DEM is proposed.Firstly,characteristic method is used to detect the shadow area in the satellite imagery.Then the shady slope and cast shadow area can be detected by model method using DEM data.The shadow is divided into 8 categories with the cause of formation.And then,the compensation method of shadow area and topography correction model are used to correct the optical remote sensing satellite imagery.The results suggest that the proposed method can recover the shadow area information effectively and weaken the effect of terrain.

A New Method of Constructing a Central Time-space Map

WANG Lina, LI Xiang, JIANG Nan, YANG Zhenkai, YANG Fei

2018, 47(1): 123-132. doi:10.11947/j.AGCS.2018.20170180

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A central time-space map is an effective method for representing time distance from any positions to a given point on a map.We proposed a new method of generating a central time-space map based on moving least squares(MLS).Compared with other methods,our method solved the following 3 problems:①the law of consistency of distance was used to keep the same scale of a time-space map and its original map;②we used some constraints to adjust topological errors generated by the process of transformation;③many visualization methods were used to represent a time-space map's distortion.Finally,we took real trains' timetable data in China in 2016 as a case study to generate a time-space map with Beijing as the center.The results showed that the time distance relationship between Beijing and other cities from a different perspective and were also helpful for further discovering some knowledge and trends of the development of railway transportation in China.

Research on Ocean Tide Loading and Ocean Tide Loading Displacement Model Estimated by GPS

ZHAO Hong

2018, 47(1): 133-133. doi:10.11947/j.AGCS.2017.20170181

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