2014 Vol. 39, No. 9
Objective Ambiguity resolution is a core issue in high precision GNSS carrier phase positioning,inclu-ding both ambiguity estimation and ambiguity validation.Ambiguity estimation fixes the float ambigu-ity to its integer value utilizing its precision information:an integer least-squares problem.Ambiguityvalidation evaluates the estimated ambiguity and whether it can be treated as the correct:aprobabilitystatistics problem.Incorrectly validated ambiguity can lead to wrong positioning results at the decime-ter or larger bias.Therefore,ambiguity validation will have a direct impact on the reliability of ambi-guity resolution and positioning results based on the theory of ambiguity validation.We introduce sev-eral widely used ambiguity validation methodologies.The advantages and disadvantages of each meth-od are compared and analyzed,from the perspective of the background theory and practicability.Atlast,we address the outlook for future research in ambiguity validation.
Objective Considering the limitations of TurboEdit,an improved cycle-slip detection method namedthe two-step method is proposed for dual-frequency GPS receivers.Firstly,the new method detectswide-lane cycle slips based on test values computed from a forward-backward moving window for MW(Melborne-Wubbena)combination observations,and then detects cycle slips in the carrier phase L1based on the check conditions extracted from a moving window of the first-order difference quotient ofPIR(phase ionospheric residual)combination observations which have been removed wide-lane cycleslips.The experimental results show that the new method can effectively suppress noise,and superiorto TurboEdit for detecting small cycle slips.It can also explore when cycle-slips exist in both two car-rier phases.
Objective We introduce a measurement for extracting the regional ionosphere TEC(total electron con-tent)from GPS dual observations in detail.From the basic principles for extracting TEC using GPS,we focus on solving two key problems.One was to improve the accuracy of pseudo-range observa-tions,and the other was to detach the DCB(differential code bias)of the satellites and receivers.Fur-thermore,the extracted TEC and TEC calculated by the CODE(Center for Orbit Determination in Eu-rope)were used as an ionospheric delay correction in a single-frequency point positioning model.Theresults show that the point accuracy can reach to 0.2-0.4musing the extracted TEC correction,a sig-nificantly improvement over the use of an interpolated GIM correction.
Objective A new combined LS(CLS)method is proposed which considers the random error in a designmatrix after a brief introduction of TLS and its iteration algorithm and the SVD algorithm.The newalgorithm can be applied for TLS parameter estimation,so that TLS can be integrated with classicalLS in theory.By proposing rigorous accuracy assessment formulas for TLS under the new algorithm,this paper solves the bottleneck problem which restricts the application of TLS,and then shows thefeasibility and correctness of the new method through examples.The research results are meaningfulnot only for TLS theory,but also for the whole data processing theory.
Objective Adjustment methods for parameter estionation were basically developed on the basis of addi-tive random error models.With advances in the technology for modern geodetic observation,measure-ment errors can change with functional models such as EDM,GPS and VLBI baselines.Thus,ran-dom errors in measurements are proportional to the true values of the measurements themselves.Ob-servational models of this type are called multiplicative error models.The purpose of this paper is tocomplement or extend the work of Xu and Shimada(2000)to mixed additive and multiplicative errormodels.We briefly discuss three least squares(LS)adjustment methods for parameter estimation inmixed additive and multiplicative error models.In case of the weighted LS adjustment,we explicitlydescribe the biases in the adjusted parameters.Then,we construct a bias-corrected weighted leastsquares estimator.Finally,we demonstrate that the bias-corrected weighted LS method is optimal andunbiased using a simulated example.
Objective Ill-posed problems exist in the gray system GM(1,1)model.Seriously ill-posed informationmatrices will occur in larger original measured data values.Reasons which cause ill-posed informationmatrices in GM(1,1)modesl are analysized in detail.A method to adjust the measurement unit of theoriginal measured data values to reduce the conditional number of information matrices is put forward.Based on GM(1,1)model theory,we show that an adjustment to the measured data units of measure-ment does not affect the model relative residuals,average residuals,or prediction accuracy.Numericalexperiments and analysis demonstrate that this method of adjusting the measurement unit algorithmfor a GM(1,1)model is easy to implement,simple,accurate,and widely applicable.
Objective The dissipative energy of the GOCE satellite is fitted by a Fourier series,this method cansolve the calculation problem for dissipative energy when the GOCE gravity field model is recoveredbased on an energy conservation approach.The Helmert-Wolf parameter estimation method is adoptedto provide an integer estimate for potential coefficients,the energy constant and Fourier series fittingparameters of dissipative energy.The potential coefficients are solved by elimination for the regionalparameter by least squares.Three gravity field models,up to the degree and order 100,namedGOCE-ECP01S,GOCE-ECP02Sand GOCE-ECP03S,are recovered based on the GOCE orbits for103-days from 2009-11-01to 2010-02-12.Finally,the models are compared with the existing EIGEN-6C,ITG-CHAMP05Sand GOCO03Smodels.The results show that the GOCE-ECP01Smodel is themost accurate when GOCE satellite dissipative energy is fitted by an one order Fourier series which ishigher than the ITG-CHAMP05Smodel,but lower than the model GOCO03S.The geoid error in theGOCE-ECP01Smodel is±3.2cm for the degree and order 100,but the precision of zonal coefficientsis low due to the polar gap.
Objective A water diversion project in Central Yunnan exhibited several typical characteristics of theoverall survey region,such as the extraordinarily long span,the high average altitude,and large ele-vation changes.Therefore,difficult to build independent coordinate system for this project.Based onthe theory of projection distortion,we propose a key technology solutions composed of two parts.First,using the 1°projection zone to replace the regular 3°projection zone,Gauss projection distor-tion was effectively controlled.Second,a method for selecting a compensation projection plane wasdeducted to satisfy the needs of this water diversion project.An optimized solution for this project wasfound using the proposed independent coordinate system and efficiently controlled,the maximum com-prehensive deformation for this water diversion project in Central Yunnan.
Objective The visualization of vector fields has become an important means for the expression of flowsin many different disciplines.In order to express a marine fluid flow's structure more clearly,based oncritical point theory,we present a new seeding point placement strategy and a new adaptive-step com-putation model.Considering a local cell's velocity and flow direction jointly with two degrees of free-dom,it adjusts the steps by using two parameters and realizes the step acceleration and decelerationaccording to the flow direction.For the placement of the global flow field streamlines,we also give anew streamline density adjustment strategy based on a smoothing window.Experimental analysis of aglobal ocean flow visualization shows that this algorithm better expresses the marine fluid flow struc-ture and suggests a reasonable placement of streamlines.
Objective The complexity of geometry-based methods for integrating vector data and DEM grids seri-ously limits their application on large area.To overcome this deficiency,a novel“drift”algorithm isput forward and designed based on the idea of grid cell decomposition and the partition model of thespherical Degenerate Quadtree Grid(DQG).An experiment was developed in which USGS GTOPO30DEM data,ASTER GDEM data and the 1∶1 000 000 DCW roads data sets for the China andChongqing area were used test the proposed drift algorithm.Tests show that the the“drift”algorithmis only 25% of the traditional one,and the mean error of the drift operation on vector nodes can becontrolled within about half a DQG cell.Moreover,the phenomenon of vector polyline going acrossthe multi-scale DEM grids would are avoided completely.
Objective Geometric matching of electronic map data for navigation is one of the most common meth-ods used for road network object matching:threshold selection is the precondition for geometric matc-hing.Nowadays,there are many disadvantages in the existing methods,such as poor adaptability,1066 large errors,low precision.Aiming to solve these drawbacks,we took the advantage of multimodaldistribution characteristics in the matching data,and proposed a dynamic calculation method for matc-hing threshold based on the method of maximum classes square error(OSTU method).In this re-search,the fundamental principles and implementation process are introduced and detailed.Experi-mental results show that the proposed method has advantages of better self-adaptivity and higher accu-racy.Furthermore,the proposed method is easy to realize,and has potential to be widely used.
Objective In the era of big data,efficient spatial indexes need to be established quickly for massivespatial data.The R-tree spatial index built by the sort tile recursive(STR)technique has excellentquery performance but low efficiency when building.We propose an R-tree bulk loading algorithm u-sing a STR technique based on general purpose computing on a GPU.A linear array structure is usedto store an R-tree and an overall sorting algorithm is used instead of segmented sorting.Experimentsshow that our proposed algorithm achieves up to a 27speedup.Our experiments also indicate that thespeedup increases as the data becomes larger.We use a query algorithm on the GPU to verify the R-tree bulk loading algorithm;finding that it has good query performance.Our algorithm takes advan-tage of the parallel processing capacity of the GPU and achieves high efficiency which shows that thetechnology of GPU computing has broad applicability in the spatial indexing field.
Objective Based on the modeling of error ellipses andεerror bands,we present a model for the Et fieldwhich includes REM field and the extremum field,where Et is the DEM terrain representation error.Then,a construction method of Et field is established.Taking the terrain of plain river network,lo-ess hill and Qinling mountains as test data,we analyze the basic characteristics of the Et field by acomparative analysis method.Experimental results show Experimental results show the conclusions asfollows:(1)the Et field could reflect the spatial distribution of DEM terrain representation error intu-itively and accurately and deserves to research.(2)Et is closely related to the landform complexity ofthe area presented by DEM and presents significant spatial structure distribution characteristics.Meanwhile,RMS of Et shows a feature of the curve with the resolution of DEM increasing.(3)Asthe unoptimistic accuracy of existing RMS estimation models of Et,the quantitative simulation of theregional topographic complexity should be completed scientifically and accurately at first to achieve thehigh-accuracy RMS estimation of Et.
Objective Urban storm floods cause dramatically property damage and severely influence on city life.It is an emergency issue and a knotty problem to be solved.Much research focuses on raster-basedDEM and hydrodynamic equations to simulate inundation processes.Nevertheless,current methodsstrictly require hydrology data and are unable to model accurately the urban terrain features.By em-ploying a constrainted Delaunay triangular irregular network(CD-TIN),complex urban surfaces areprecisely modeled in detail.Urban basins,serving as simulation units,are generated based on the wa-ter flow rules for triangular surface.Referring to the capacity of the drainage and complexity of urbanterrain features,we introduce the basin runoff yield and confluence method for spatio-temporal calcu-lation step by step.In order to obtain the inundated extent and water depth,a numerical solution isput forward based on the concept of triangular-prism sets through dichotomy.The main campus ofBeijing Normal University(BNU)is used as a case to construct the CD-TIN and to simulate the“7.21storm”inundation event,2012,to test the usability and suitability of the method presented.Simula-tion water depths are compared with the observation data,showing that the CD-TIN based method forurban inundation simulation is effective and reliable.The CD-TIN based simulation method will beuseful for urban flood emergency preparation,storm flood risk analysis and urban reforms in potentialinundation areas.
Objective Aiming to seamlessly integrate elaborated engineering facilities models and large scale land-scape models as well as to support the sharing and application life cycle of three-dimensional GIS,wepropose a new method to automatically build complex models of engineering facilities using designedparameters.The traditional 3DGIS data model is extended to satisfy the demands for integration andsynchronous updating of geometric models and their related parameters.Finally,the validity and fea-sibility of this method are demonstrated through its application for bridge modeling.The proposedmethod facilitates seamless integration of GIS and CAD.
Objective The derivative of magnetic vector components plays an important role in the magnetic targetinterpretation process.A boundary effect problem is found in the computation of higher order deriva-tives of magnetic potential using the common methods such as the fast Fourier transform algorithm inactual applications.The paper presents a solution based on aπ/2phase-shifted cosine transform andits time-differentiation.Unified formulas for calculating the derivatives of magnetic vector componentswere deduced,and then applied to the directional analytic signals method.An analysis and comparisonof magnetic field data between the rectangular prism source model and cosine transform method showthat the influence of boundary effect can be avoided.The proposed method not only has higher preci-sion and stability,but also doesnot require additional data and algorithm complexity for extendingedge and filter processing.
Objective ZiYuan-3not only provides distortionless standard scenes for sensor corrected products butalso long strip scenes,whose length could extend almost 600km.The long strip scenes are similar tostandard scenes,whose mismatch and elevation errors,introduced by production procedures are ignor-able.A rational function model(RFM)for long strip scenes is provided.The image space affinetransformation is used to eliminate attitude and ephemeris errors in long strip scenes,and sub-pixelorientation accuracy is made available.When ground control points(GCPs)are deployed around thecorners of the survey area,the RMS(root mean square)of the plane and elevation of long strip sceneswas 2.5mand 1.6mrespectively.The accuracy is similar to the single standard scenes.
Objective As the deformation among multi-view images from the Chang’E-1CCD is non-rigid,giventhe non-planarity of the moon surface,the traditional methods based on the affine transform model arenot suitable for super-resolution correction.For this reason,a new optical flow based super-resolutionframework is proposed.In the framework,the BTV method is employed to estimate a high resolutionimage iteratively.The initial values for a high resolution image are generated by all multi-view imagesthat are registered by optical flow,while the optical flow fields are updated each iteration.Experimen-tal results show that the proposed method performs better for the super-resolution of Chang’E-1CCDmulti-view images than affine transform based methods.The resolution of the reconstructed image isgreatly improved and more details are visible without ringing-effects.
Objective The Bag-of-Words(BoW)approach has lower retrieval accuracy performance for remotesensing image retrieval.The rate of correct results is very low especially when target textures are sim-ilar.To overcome this shortcoming,an indirect comparison between a query and target image basedon local invariant feature of the background image is proposed.The solution has two phases:theprocess of building a database and a retrieval process.After building a database,a search of the nea-rest neighbor feature in a query image in the feature space of the image dataset through an approximateKD-Tree is executed,then their relationship is recorded.The relationship can be used in calculatingsimilarity between a query and target image during a retrieval procedure.Experiments show that theproposed method has a better recognition performance than that of the BoW and,at the same time,needs less storage space for saving local invariant features.
Objective The mosaicking of point clouds is a key step in point cloud processing.We propose a pointcloud mosaicking technology for multi-station laser scanning based on 2Dimage matching and 3Dcor-responding feature point refinement to solve the problems in existing point cloud mosaicking method-ologies for multi-station laser scanning,such as low efficiency,poor accuracy,and low automation.Firstly,the 2Dimages are generated from the derivative information from laser scanning data using in-terpolation algorithms.Secondly,2Dcorresponding feature points are obtained using GPU accelera-tion SIFT image matching,eliminating gross errors.Finally,3Dcorresponding feature points are ac-quired using an inversion algorithm;identifying whether they are same corresponding feature points inthe 3Dpoint cloud.Experiments demonstrate the feasibility and effectiveness of the proposed method.
Objective A slope estimation model and algorithms were advanced based on the repeat ground track el-evation data collected from the Geoscience Laser Altimeter System(GLAS)on board the Ice,Cloudand land Elevation Satellite(ICESat).Innovative algorithm steps show and confirm the referencestarting point(RSF)on the reference track(RT)and the corresponding starting point(CSF)on otherrepeat corresponding track(CT).The slope model and algorithms were validated with the elevationdata from ground track 420collected by ICESat/GLAS when passing over the Beijing area during2003-2009.The RMS and standard deviation of slope differences between RT and CTs were deducedand discussed.The results show that the RMS and standard deviation(STD)of the slope differencesincrease with the increase in the STD/RMS of the separation between the CT and RT.The slopedrawing on a geographic map were coincidental with the geographical ground truth when comparedwith an image obtained from Google map.The calculated slope based on ICESat/GLAS data was com-pared to that based on SRTM DEM data demonstrating the reliability of these results.
Objective Estimation of processes for slow change in small scale surfaces is one of the main advantagesof PSInSAR technology.We present a mathematical framework for the datum connection for time-space referencing,applying it to 500scenes composed of Envisat ASAR images covering about 200 000km2 of the North China Plain,obtained the rate of ground subsidence in the study area during the pe-riod of 2006-2010.The experimental results show that:(1)the multiple subsidence centers in NorthChina Plain were still in an evolving state,connecting Beijing,Langfang,Tianjin,Renqiu,Cang-zhou,Botou,Hengshui,Dezhou,Nangong and Handan into a continuous area.(2)The most promi-nent ground subsidence was in Tianjin’s Jinghai and Binhai areas having average subsidence rates of62mm/a and 67mm/a along the line of sight,respectively.The subsidence of the old centers,to theeast of Beijing,Cangzhou,Botou -Hengshui -Dezhou,Handan,had rates of 36mm/a,34mm/a,37mm/a,29mm/a,respectively.(3)The experimental results were validated with leveling data inTianjin area.The difference between the two methods is less than 10mm,which shows that the re-sults obtained by the PSInSAR technique are consistent with those obtained by leveling.(4)The re-sults here presented can be used as development prevention reference measures of regional ground sub-sidence.