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Determination of ocean tide loading displacements in hong kong using GPS technique

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Science China Earth Sciences 2010年第7期53卷 993-1007页

作者： YUAN LinGuo1,3, DING XiaoLi1, SUN HePing2. Zhong Ping1,3 & CHEN Wu1 1 Department of land {2. and geo-informatics, The hong kong polytechnic University, Kowloon, hong kong, China 2.Key Laboratory of Dynamic geodesy, Institute of geodesy and geophysics, Chinese Academy of Sciences, Wuhan 430077, China 3 Department of {2. Engineering, School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China Department of land surveying and {2.-informatics The Hong Kong Polytechnic University Kowloon Hong Kong China Department of surveying Engineering School of Civil Engineering Southwest Jiaotong University Chengdu China Key Laboratory of Dynamic geodesy Institute of Geodesy and Geophysics Chinese Academy of Sciences Wuhan China

Ocean tide loading (OTL) displacements of eight principal constituents at 12.sites in hong kong were determined using more than eight years of continuous GPS observations. Parameters of the OTL displacements were estimated using daily GPS solutions obtained with precise point positioning (PPP) technique. The results were compared with predictions from seven latest global ocean tide models. Gravity measurements of OTL in hong kong were also used to validate the GPS results. The study shows that the results from both the GPS and gravity measurements agree best with the GOT4.7 and NAO99b models, when the K1 and K2.constituents are excluded. The agreements between the GPS and the model estimates are generally at sub-millimeter level in both the horizontal and vertical directions, exc{2. for S2. K2.and K1 constituents that have relatively larger errors. After removing the systematic biases between the GPS and the model estimates, the misfits of M2. S2. N2. O1, P1 and Q1 at all sites are within 0.5 and 1.0 mm in the horizontal and the vertical directions, respectively, whereas K1 and K2.show relatively larger misfits of up to 2.3 mm. Both the GPS and the gravity S2.estimates have large biases with unknown reasons when compared with the modeled values, which needs to be further investigated. The study demonstrates that GPS is capable of estimating the OTL displacements with the same accuracy as the model predictions, especially for coastal areas.

关键词： GPS ocean tide loading ocean tide model site displacement

A Voronoi-based spatial algebra for spatial relations

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Progress in Natural Science:Materials International 2002年第7期 50-58页

作者： LI Zhilin , ZHAO Renliang and CHEN Jun(1. Department of land surveying and {2.-informatics, The hong kong polytechnic University, hong kong, China 2. National {2.metries Center of China, Beijing 100044, China) Department of land surveying and {2.-informatics，The hong kong polytechnic University，hong kong，China Department of land surveying and {2.-informatics，The hong kong polytechnic University，hong kong，China National geometrics Center of China，Beijing 100044，China National geometrics Center of China，Beijing 100044，China

Spatial relation between spatial objects is a very important topic for spatial reasoning, query and analysis in geographical information systems (GIS). The most popular models in current use have fundamental deficiencies in theory. In this paper, a generic algebra for spatial relations is presented, in which (i) appropriate operators from set operators (i. e. union, intersection, difference, difference by, symmetric difference, etc. ) are utilized to distinguish the spatial relations between neighboring spatial objects; (ii) three types of values are used for the computational results of set operations-content, dimension and number of connected components; and (iii) a spatial object is treated as a whole but the Voronoi region of an object is employed to enhance its interaction with its neighbours. This algebra overcomes the shortcomings of the existing models and it can effectively describe the relations of spatial objects.

关键词： spatial relations Voronoi-based algebra spatial algebra topological relations.

A probabilistic paradigm for handling uncertain objects in GIS by randomized graph algebra

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Progress in Natural Science:Materials International 2003年第9期 10-19页

作者： SHI Wenzhong and WU Huayi(Advanced Research Centre for Spatial Information Technology, Department of land {2. and geo-informatics, The hong kong polytechnic University, hong kong, China)

Probability theory faces difficulties when it is applied to describing uncertain objects in geographic information system(GIS). This is mainly due to the fact that an object in GIS is normally described by a series of discrete vertexes. Modeling uncertainty ob-jects should be therefore based on error of the composed vertexes. This type of model is normally complex and relatively difficult to imple-ment because of many unknown factors, such as the number of vertexes of a polygon, error nature of each individual vertex and error cor-relation among the vertexes. In this paper, a probabilistic paradigm for handling uncertain objects in GIS by randomized graph algebra ispresented. The theoretical basis for this paradigm is the randomized graph algebra-a probability theory for graph-which is newly pro-posed in this study. Classical probability theory is based on numerical algebra and is also an extension of numerical algebra by further defin-ing probability density within a numerical domain. In the same token

关键词： GIS uncertain objects graph algebra measure space.

Statistical characteristics of chlorophyll-a concentration in hong kong's coastal waters

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Journal of geographical Sciences 2002年第3期12卷 331-342页

作者： CHEN Xiaoling, Yok Sheung Li, LI Zhilin(1. Dept. of Civil and Structural Engineering, The hong kong {2. University, hong kong, China 2. National Laboratory for Information Engineering in surveying, Mapping and Remote Sensing (LIESMARS), Wuhan Uni Dept. of Civil and Structural Engineering The Hong Kong Polytechnic University 香港 Wuhan University National Laboratory for Information Engineering in Surveying Mapping and Remote Sensing (LIESMARS) Wuhan 430072 Dept. of land {2. & geo-informatics The Hong Kong Polytechnic University 香港

In this paper seven of the ten Water Control Zones (WCZs) in hong kong's coastal waters with monthly or bi-weekly sampling data of 17 parameters collected at 37 monitoring stations from 1988 to 1999 were selected to analyze the spatial and temporal variations of chlorophyll-a and its influencing factors. Cluster analysis was employed to group the monitoring stations based on the structure of the data set. Multiple step regression was employed to determine the significant influencing factors of chlorophyll-a level. The results suggest that all the monitoring stations could be grouped into two clusters. Cluster Ⅰ with frequent red tide incidents comprises two WCZs which are semi-enclosed bays. Cluster Ⅱ with less red tide occurrence comprises the other five WCZs in an estuarine environment in the west. For both clusters, the organic contents indicator, BODS, was a common significant influencing factor of the chlorophyll-a level. Nitrogen and light penetration condition related to turbidity, total volatile solids and suspended solids had more influence on the cholophyll-a level in Cluster Ⅰ than in Cluster Ⅱ, while phosphorus and oceanographic conditions associated with salinity, temperature, dissolved oxygen and pH were more important in Cluster Ⅱ than in Cluster Ⅰ. Generally, there was a higher average chlorophyll-a level in winter and autumn in a year. The chlorophyll-a level was much higher in Cluster Ⅰ than in Cluster Ⅱ among all seasons. Although the chlorophyll-a concentration had great variations from place to place in hong kong's coastal waters, it seemed to have a common long term fluctuation period of 8-10 years with a high-low-high variation in the period in the whole region, which might be influenced by other factors of global scale.

关键词： hong kong's coastal waters chlorophyll-a concentration spatial-temporal variations

A VORONOI-BASED ALGORITHM FOR POINT CLUSTER GENERALIZATION

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A VORONOI-BASED ALGORITHM FOR POINT CLUSTER GENERALIZATION

第十一届几何与图学国际会议

作者： Haowen YAN Zhilin LILanzhou Jiaotong University Lanzhou 730070 ChinaDepartment of land surveying and {2.-informatics The hong kong polytechnic University Kowloon hong kong

＜正＞The main purpose of the algorithms for point feature generalization is to correctly transmit information contained by point clusters with the reduction of point number, however two groups of existing algorithms are not satisfactory: the incremental algorithms for settlement selection （Langran and Poiker, 1986;van Krevel et al, 1995） can’t deal with topological information well, while the Voronoi-based algorithm （Ai and Liu, 2.02. doesn’t take into consideration the importance values （thematic information） of points. To overcome their shortcomings, an integrated algorithm is given. The new algorithm employs two methods to ensure different kinds of information can be transmitted correctly: （1） determine the point number on resulting maps by the radical law （Topfer and Pillewizer, 1966）, so that statistical （positional） information is transmitted correctly;（2. recursively construct Voronoi diagrams of the retained points, and delete points by comparing the significance value of a point with those of its Voronoi neighbors, so that topological, thematic and geometrical information are transmitted correctly. The drawback of this algorithm is that the symbolization of point features is not considered, which may cause overlap and congestion of map symbols on resulting maps.

关键词： Point feature generalization Voronoi diagrams Algorithms

IONOSPHERIC EFFECTS ON GPS NAVIGATION IN LOW-LATITUDE AREA

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IONOSPHERIC EFFECTS ON GPS NAVIGATION IN LOW-LATITUDE AREA

第一届交通运输工程国际学术会议

作者： GAO Shan1, 2.and CHEN Wu2.1School of Civil Engineering, Southwest Jiaotong University, Chengdu, Sichuan, China, 610031 2.ept. of land surveying and geo-informatics, The hong kong {2. University, hong kong

Ionospheric effects are the major constraints for GPS navigation. Especially, at low latitude, ionospheric delay varies greatly both in space and time. Even for short baselines, ionospheric effects cannot be cancelled out with double difference algorithm. Strong ionospheric disturbances are also observed in the region. In this paper, ionospheric behavior in hong kong is investigated by using a dense reference network. The effects of ionospheric disturbances on GPS receiver, such as loss of lock, gross error and measurement noise are studied.

关键词： GPS navigation ionospheric delay loss of lock cycle slip

Relativistic Effects in Space geodesy

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Relativistic Effects in Space Geodesy

作者： HUANG Cheng DING Xiaoli CHEN Yongqi 1 Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 2.0030 2.Dept. of land {2. and geo-informatics, hong kong polytechnic University, hong kong

Space geodesy involves the measurement or monitoring of variation of spatial motion of the Earth as a whole and mass motion of each layer of the Earth, using space - based techniques. They concern the space and time, which belong to the realm of General Relativity. With the rapid increase of space - based observational accuracy, the relativistic effects in Space geodesy must be taken into account to make full use of the information of high precise observation. This paper will review the principal relativistic effects in Space geodesy briefly.

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Monitoring Crustal Deformations with Radar Interferometry: A Review

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Journal of Southwest Jiaotong University(English Edition) 2004年第2期12卷 148-158页

作者：刘国祥丁晓利黄丁发 School of Civil Engineering Southwest Jiaotong University Department of land surveying and {2.-informatics The Hong Kong Polytechnic University

The crustal movements, probably motivating earthquakes, are considered as one of the main geodynamic sources. The quantitative measurements of ground surface deformations are vital for studying mechanisms of the buried faults or even estimating earthquake potential. A new space-geodetic technology, synthetic aperture radar interferometry (InSAR), can be applied to detect such large-area deformations, and has demonstrated some prominent advantages. This paper reviews the capacity and limitations of InSAR, and summarises the existing applications including some of our results in studying the earthquake-related crustal motions. Finally it gives the outlook for the future development of InSAR.

关键词： Satellite SAR interferometry Earthquake Crustal deformation Monitoring

Stochastic Model of GPS/BD Combined Standard Single Point Positioning

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Stochastic Model of GPS/BD Combined Standard Single Point Po...

第三届中国卫星导航学术年会

作者： Wenkun Yu 1,Wujiao Dai 1,Xiaoli Ding 2.Wentao Yang 2.Xiao Gao 1 1 School of geosciences and Info-physics Engineering,Central South University,Changsha,Hunan,China 2.Department of land {2. and geo-informatics,The hong kong polytechnic University,Hung Hom,Kow Loon,hong kong

Reasonable determination of weights is the key factor in giving full play to advantages of GPS/BD combined ***,Helmert VCE （Variance Component Estimation） is employed aiming at adjusting the variance-ratio between the two heteroscedastic ***,the precise priori weight matrix can enhance the convergence of iteration methods based on posteriori information,reduce the iteration’s ***,system related errors,together with outliers,influence the estimation,leading to a distorted stochastic ***,in this paper,based on robust Helmert VCE and using integrated priori accuracy,taking various error sources into consideration,an initial weighing method for combined system is suggested.

关键词： GPS/BD robust Helmert stochastic model