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Global precision analysis of carrier phase relative positioning in BeiDou navigation satellite system and United States global positioning system

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Science China Earth Sciences 2019年第4期62卷 733-749页

作者： Letao ZHOU Dingfa HUANG Wei FENG Wu CHEN Xi ZHANG Li YAN department of surveying and geo-informatics Faculty of Geosciences and Environmental EngineeringSouthWest JiaoTong University department of land surveying and geo-informatics Hong Kong Polytechnic University

In this paper, we derived a high-efficiency formula for calculating the precision of carrier phase relative positioning,analyzed the various factors that affect the positioning accuracy using the carrier phase, and proposed the concept of using a frequency dilution of precision to describe the quantitative effect of different frequency combinations on the positioning precision. To this end, we computed and plotted the global spatial distribution map of the relative positioning dilution of precision for single-day solution, half-hour solution, and single-epoch solution of the global positioning system(GPS), regional Beidou navigation satellite system(BDS2), future global Beidou navigation satellite system(BDS3), and their fusion *** processing software with autonomous intellectual property rights(GCN and VENUS/ARSNet), we solved the measurement data and examined the positioning precision of the single-day solution and single-epoch solution of GPS and *** analysis demonstrated that the B1/B2 frequency positioning precision of BDS2 was better than that of L1/L2 frequency positioning of GPS, but the positioning precision of the BDS2 is worse than that of GPS over most of the service region of the BDS2. Further, the positioning precision of BDS3 is better than that of GPS in the Asia-Pacific region, while it is the opposite in other regions. Based on these conclusions, we put forth some optimization recommendations regarding the signal frequency of the navigation system and GPS measurement standards to serve as references for optimizing the system performance and formulating standards.

关键词： BeiDou navigation satellite system Relative positioning Dilution of precision Frequency dilution of precision Spatial-temporal availability

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SAR image despeckling with a multilayer perceptron neural network

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International Journal of Digital Earth 2019年第3期12卷 354-374页

作者： Xiao Tang Lei Zhang Xiaoli Ding department of land surveying and geo-informatics The Hong Kong Polytechnic UniversityKowloonHong Kong

Speckle noise in synthetic-aperture radar (SAR) images severely hindersremote sensing applications;therefore, the appropriate removal ofspeckle noise is crucial. This paper elaborates on the multilayerperceptron (MLP) neural-network model for SAR image despeckling byusing a time series of SAR images. Unlike other filtering methods thatuse only a single radar intensity image to derive their parameters andfilter that single image, this method can be trained using archivedimages over an area of interest to self-learn the intensitycharacteristics of image patches and then adaptively determine theweights and thresholds by using a neural network for imagedespeckling. Several hidden layers are designed for feedforwardnetwork training, and back-propagation stochastic gradient descent isadopted to reduce the error between the target output and neuralnetwork output. The parameters in the network are automaticallyupdated in the training process. The greatest advantage of MLP is thatonce the despeckling parameters are determined, they can be used toprocess not only new images in the same area but also images incompletely different locations. Tests with images from TerraSAR-X inselected areas indicated that MLP shows satisfactory performance withrespect to noise reduction and edge preservation. The overall imagequality obtained using MLP was markedly higher than that obtainedusing numerous other filters. In comparison with other recentlydeveloped filters, this method yields a slightly higher image quality,and it demonstrates the powerful capabilities of computer learningusing SAR images, which indicate the promising prospect of applyingMLP to SAR image despeckling.

关键词： Multilayer perceptron synthetic aperture radar despeckling neural network

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A detailed rock density model of the Hong Kong territories

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geodesy and geodynamics 2024年第1期15卷 75-81页

作者： Albertini Nsiah Ababio Robert Tenzer department of land surveying and geo-informatics Hong Kong Polytechnic UniversityHong KongChina

We used the geological map and published rock density measurements to compile the digital rock density model for the Hong Kong *** then estimated the average density for the whole *** to our result,the rock density values in Hong Kong vary from 2101 to 2681 kg·m^(-3).These density values are typically smaller than the average density of 2670 kg·m^(-3),often adopted to represent the average density of the upper continental crust in physical geodesy and gravimetric geophysics *** finding reflects that the geological configuration in Hong Kong is mainly formed by light volcanic formations and lava flows with overlying sedimentary deposits at many locations,while the percentage of heavier metamorphic rocks is very low(less than 1%).This product will improve the accuracy of a detailed geoid model and orthometric heights.

关键词： Density model Rock types Gravimetric modeling Hong Kong

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The effect of topographic density variations on the geoid and orthometric heights in Hong Kong

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geodesy and geodynamics 2024年第5期15卷 495-503页

作者： Albertini Nsiah Ababio department of land surveying and geo-informatics Hong Kong Polytechnic UniversityHong KongChina

Utilizing the adopted average topographic density of 2670 kg/m^(3)in the reduction of gravity anomalies introduces errors attributed to topographic density variations,which consequently affect geoid modeling ***,the mean gravity along the plumbline within the topography in the definition of Helmert orthometric heights is computed approximately by applying the Poincar e-Prey gravity reduction where the topographic density variations are *** Helmert orthometric heights of benchmarks are then affected by *** errors could be random or systematic depending on the specific geological setting of the region where the leveling network is physically established and/or the geoid model is *** example of systematic errors in orthometric heights can be given for large regions characterized by sediment or volcanic deposits,the density of which is substantially lower than the adopted topographic density used in Helmert's definition of *** same applies to geoid modeling *** this study,we investigate these errors in the Hong Kong territory,where topographic density is about 20%lower than the density of 2670 kg/m^(3).We use the digital rock density model to estimate the effect of topographic density variations on the geoid and orthometric *** results show that this effect on the geoid and Helmert orthometric heights reach maxima of about 2.1 and 0.5 cm,*** results provide clear evidence that rock density models are essential in physical geodesy applications involving gravimetric geoid modeling and orthometric height determination despite some criticism that could be raised regarding the reliability of these density ***,in regions dominated by sedimentary and igneous rocks,the geological information is essential in these applications because topographic densities are substantially lower than the average density of 2670 kg/m^(3),thus introducing large systematic errors in geoid and orthometric

关键词： Rock density geoid Topography Heights Leveling network

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Low-cost cloud computing solution for geo-information processing

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Journal of Central South University 2016年第12期23卷 3217-3224页

作者：高培超刘钊谢美慧田琨 department of land surveying and geo-informatics Hong Kong Polytechnic University Institute of geomatics Department of Civil EngineeringTsinghua University

Cloud computing has emerged as a leading computing paradigm,with an increasing number of geographic information(geo-information) processing tasks now running on *** this reason,geographic information system/remote sensing(GIS/RS) researchers rent more public clouds or establish more private ***,a large proportion of these clouds are found to be underutilized,since users do not deal with big data every *** low usage of cloud resources violates the original intention of cloud computing,which is to save resources by improving *** this work,a low-cost cloud computing solution was proposed for geo-information processing,especially for temporary processing *** proposed solution adopted a hosted architecture and can be realized based on ordinary computers in a common GIS/RS *** usefulness and effectiveness of the proposed solution was demonstrated by using big data simplification as a case *** to commercial public clouds and dedicated private clouds,the proposed solution is more low-cost and resource-saving,and is more suitable for GIS/RS applications.

关键词： cloud computing geo-information processing geo-processing

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A general method of spatio-temporal clustering analysis

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Science China(Information Sciences) 2013年第10期56卷 158-171页

作者： DENG Min LIU QiLiang WANG JiaQiu SHI Yan department of surveying and geo-informatics Central South University

Spatio-temporal clustering has been a hot topic in the feld of spatio-temporal data mining and knowledge *** can be employed to uncover and interpret developmental trends of geographic phenomenon in the real ***,existing spatio-temporal clustering methods seldom consider both spatiotemporal autocorrelations and heterogeneities among spatio-temporal entities,and the coupling in space and time has not been well *** this paper,a unifed framework for the clustering analysis of spatio-temporal data is proposed,and a novel spatio-temporal clustering algorithm is developed by means of a spatio-temporal statistics methodology and intelligence computation *** method is applied successfully to fnding spatio-temporal cluster in China’s annual temperature database for the period 1951 1992.

关键词： spatio-temporal clustering spatio-temporal autocorrelation spatio-temporal heterogeneity spatio-temporal data mining

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Bundle adjustment for data processing of theodolite industrial surveying system

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中国有色金属学会会刊：英文版 2001年第2期11卷 307-310页

作者：邹峥嵘丁晓利曾卓乔何凭宗 department of surveying Engineering Central South UniversityDepartment of Land Surveying and Geo-Informatics Hong Kong Polytechnic UniversityHunghom Hong Kong department of land surveying and geo-informatics Hong Kong Polytechnic UniversityHunghom Hong Kong department of surveying Engineering Central South University

The photogrammetric bundle adjustment was used in data processing of electronic theodolite industrial surveying system by converting angular observations into virtual photo coordinates. The developed algorithm has ability of precision estimation and data snooping, do not need initial values of exterior orientation elements and object point coordinates. The form of control condition for the system is quite flexible. Neither centering nor leveling is the theodolite needed and the lay out of theodolite position is flexible when the system is used for precise survey. Experiments carried out in test field verify the validity of the data processing method. [

关键词： electronic theodolite industrial surveying system bundle adjustment

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A novel method for discovering spatio-temporal clusters of different sizes, shapes, and densities in the presence of noise

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International Journal of Digital Earth 2014年第2期7卷 138-157页

作者： Qiliang Liu Min Deng Jiantao Bi Wentao Yang department of surveying and geo-informatics Central South UniversityChangshaChina department of land surveying and geo-informatics Hong Kong Polytechnic UniversityHong Kong Center for Earth Observation and Digital Earth Chinese Academy of SciencesBeijingChina

The discovery of spatio-temporal clusters in complex spatio-temporal data-sets has been a challenging issue in the domain of spatio-temporal data mining and knowledge *** this paper,a novel spatio-temporal clustering method based on spatio-temporal shared nearest neighbors(STSNN)is proposed to detect spatio-temporal clusters of different sizes,shapes,and densities in spatiotemporal databases with a large amount of *** concepts of windowed distance and shared nearest neighbor are utilized to define a novel spatiotemporal density for a spatio-temporal entity with definite mathematical ***,the density-based clustering strategy is employed to uncover spatio-temporal *** spatio-temporal clustering algorithm developed in this paper is easily implemented and less sensitive to density variation among spatio-temporal *** are undertaken on several simulated datasets to demonstrate the effectiveness and advantage of the STSNN ***,the real-world applications on two seismic databases show that the STSNN algorithm has the ability to uncover foreshocks and aftershocks effectively.

关键词： spatio-temporal clustering shared nearest neighbor windowed distance spatio-temporal density foreshocks and aftershocks data mining Digital Earth geo-spatial science geospatial data integration

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Optimum choice of parameters and numerical schemes for a regional gravimetric Moho recovery

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geodesy and geodynamics 2019年第6期10卷 417-429页

作者： Samurdhika Rathnayake Robert Tenzer department of land surveying and geo-informatics Hong Kong Polytechnic University

Despite practical limitations of isostatic theories to model the Moho geometry are well-known,gravimetric methods are often used in terrestrial studies of crustal structure in regions with a low seismic data ***,these methods are indispensable in planetary *** gravimetric methods have been *** Airy and Pratt theories are defined based on adopting a local compensation *** Vening Meinesz theory assumes a regional isostatic flexural *** Vening Meinesz regional isostatic model generally describes a respond of the lithosphere to a load more realistically than the Airy model over *** Pratt method,on the other hand,better describes a compensation mechanism of the oceanic *** application of a particular isostatic model also depends on applied numerical procedures,parameters for inversion,input data specifications,and many other *** this study,we address some basic aspects by applying local and regional isostatic models for a Moho *** also conduct a spectral analysis to assess a spectral resolution of gravity data that is optimal for a Moho ***,we inspect the influence of low-degree spherical harmonics of gravity field on a Moho *** results are validated using seismic data at the European *** results confirm a better performance of a regional compensation *** also demonstrate that a different thickness of the oceanic and continental crustal thickness should be taken into account as a priori *** analysis indicates that gravity data used for a Moho inversion should optimally have a spatial resolution between degrees 60 to *** also show that low-degree spherical harmonics do not modify significantly the Moho geometry,particularly over regions with a relatively homogenous structure of deep mantle.

关键词： Crust Gravity Moho inversion Isostasy

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Feasibility analysis of GNSS-based ionospheric observation on a fast-moving train platform(GIFT)

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Satellite Navigation 2021年第1期2卷 278-295页

作者： Shiwei Yu Zhizhao Liu department of land surveying and geo-informatics The Hong Kong Polytechnic UniversityKowloonHong KongPeople’s Republic of China

The ionospheric effect plays a crucial role in the radio communications. For ionospheric observing and monitoring, the Global Navigation Satellite System (GNSS) has been widely utilized. The ionospheric condition can be characterized by the Total Electron Contents (TEC) and TEC Rate (TECR) calculated from the GNSS measurements. Currently, GNSS-based ionospheric observing and monitoring largely depend on a global fiducial network of GNSS receivers such as the International GNSS Service (IGS) network. We propose a new approach to observe the ionosphere by deploying a GNSS receiver on a Hong Kong Mass Transit Railway (MTR) train. We assessed the TECR derived from the MTR-based GNSS receiver by comparing it with the TECR derived from a static GNSS receiver. The results show that the Root-Mean-Squares (RMS) errors of the TECR derived from the MTR-based GNSS receiver is consistently approxi-mately 23% higher than that derived from the static GNSS receiver. Despite the increased error, the findings suggest that the GNSS observation on a fast-moving platform is a feasible approach to observe the ionosphere over a large region in a rapid and cost-effective way.

关键词： Global navigation satellite system(GNSS) Total electron contents(TEC) TEC rate(TECR) Fast-moving train platform

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