2010 Vol. 35, No. 3
We introduced the basic principle and calculation method of collocation,and studied its application in numerical integration of satellite orbits.Experiments were carried out to analyze the impact of different integration steps and method orders on results of numerical integration.Proper integration steps and method orders were also determined(being identical to the default values of Bernese software,for GPS satellite).Moreover,by comparing with the results of combined integrator designed by traditional numerical integration method,some advantages of collocation method were showed as follows:a quite long step can be used;as the polynomial coefficients of each interval are worked out directly,users could get the position and velocity of satellites at any time without interpolating and fitting;due to the above two reasons,under the same precision condition,the computational efficiency of collocation is much higher than that of normal integration methods.
We propose a multi-source information autonomous navigation scheme,which composes of star sensor,ultraviolet moon sensor and the altimeter for satellite around Moon.Unscented Kalman filtering(UKF)is used in nonlinear systems.The optimal orbit of the satellite is determined by a federated Kalman filter which realizes information complement based on a new information fusion algorithm.We also compared with the extend Kalman filtering(EKF)based on information fusion.The effectiveness of the navigation scheme was implemented by numerical simulations.The simulation results show that UKF information fusion algorithm can improve the navigation precision and reliabilities.
Based on the analysis of traditional navigation methods,we study underwater geomagnetic navigation method based on ICCP technique in detail.By the analysis in theory and the comparison in real applications,we get an optimum model,which is multi-curve function model and can improve efficiently the accuracy of building geomagnetic field model.Then,we study the technique of interactive cosest contour point(ICCP)in theory and give out a completed procedure for geomagnetic navigation.In order to make the method strong practicability,we also analyze the factors,which influence the accuracy of underwater geomagnetic navigation.Finally,we give out conclusions and a lot of suggestions.
Based on the analysis of the key problems about long distance kinematic GPS data processing,we caculated the displacements of the stations in Sichuan GPS network using the data before and after 5.12 Wenchuan Earthquake.The accuracy of long distance kinematic GPS data processing was analyzed.Kinematic deformation series of Mianyan and Pixian were obtained using Yaan as a reference station.Decomposing the deformation series into mountain Longmen fault direction and its orthogonal direction,the kinematic deformation features of several stations were obtained.Results about kinematic crustal deformation of Wenchuan Earthquake show that Mianyan and Pixian move towards northwest with small amplitude of swing during the earthquake.The maximum kinematic displacements of Mianyang and Pixian were 49.2 cm and 114.1 cm respectively.In the vertical direction,the height of Mianyan decreased after uplifting 10 cm.The height of Pixian fluctuated periodically and the fluctuation range was ±13 cm.
With the observed GPS coseismic displacements of Tokachi-Oki Earthquake and its biggest aftershock,we derive the coseismic slip distributions of the two earthquakes using SBIF(sensitivity-based iterative fitting)method.A more real fault geometry and layered Earth model were considered in the inverted process.As results shown,the maximal slips of the main shock and the biggest aftershock are 3.07 m and 0.33 m respectively.The corresponding moment magnitude scale are Mw 7.94 and Mw 7.1,which is consistent with the seismic result.In addition,the slip of the aftershock is mainly located at the place the coseismic slip of the main shock is lower,which perhaps indicate that the stress of surrounding region is enlarged by the coseismic slip of the main shock and thus trigger the biggest aftershock.
A time and frequency transfer experiment based on the precise point positioning(PPP)technique was carried out using IGS 5 min and 30 s interval precise satellite clock products.The results demonstrate that the precision of time transfer based on PPP technique is up to 0.1~0.2 nanosecond and a frequency stability of 1×10-15~2×10-15is derived for averaging times of half-day,whether using IGS 5 min or 30 s interval precise satellite clock products.The results also indicate that whereas by using 30 s interval precise satellite clock products we could get a clearly improved frequency stability over that derived by using a 5 min interval precise satellite clock products in the short term.There is no significant improvement in the long term.
There are several methods usually used for parameters estimate in precise point positioning including Kalman filters,recursive least square and square root information filtering and smoothing(SRIF&SRIS).Using Kalman filter to estimate parameters for kinematic precise point positioning(PPP)post-processing has a fatal shortcoming as the positioning precision is bad before ambiguity estimates are converged.The approach of a forward-backward Kalman filter is proposed to handle this problem,which is to sequentially carry out Kalman filter twice in both forward and backward directions.The results of the first time filtering are used as the initial information for the second time filtering while the results of the second time filtering are treated as final results of kinematic PPP.This method is simple in theory and easy for programming.Both simulated dynamic positioning test using static data and airborne dynamic positioning test were carried out.The results demonstrate that the new approach can achieve equivalent positioning accuracy as other methods.
We present an algorithm to detect and diagnose the fault with two classes neural networks for the fault in observations of dynamic precise point positioning occurs.At first,the first neural network training samples online is used to improve the reliability of dynamic model.The second neural network can automatically detect failures,position and delete the fault of observations,and the observations processed can further improve the contribution of dynamic model to the result of navigation.In the data of aircraft,the algorithm can detect the fault of observations,improve the percent of diagnosis and control the influences of the fault to the result of navigation.
Based on the introduction of fully non-normalized spherical harmonics,Clenshaw summation does not need a single spherical harmonics calculation.We compared Clenshaw summation method with standard forward column method in the calculation of time and analyzed the stability of these two methods by numerical tests.Then,we give the results of the tests.Finally,the applicability of geoid undulation computed based on Clenshaw summation method was discussed,which offers a reference for high-precision calculation of the geoid.
Four traditional VRS stochastic modeling methods and the VENUS method proposed by the authors were given.Comparison of these methods from different aspects,including posterior variances,ADOP,F-ration,filtered residual were comprehensively analyzed.Test results show that the effectiveness of the Standard,SNR and the Elevation-dependent stochastic modeling methods are not very ideal.Meanwhile,both the Adapt and the VENUS method take on their own advantages and disadvantages.Hence,it is advisable to integrate all of these advantages into one new method.
Based on the linear relation between the cross-coupling correction and 5 cross-coupling monitors,the method for modifying the coefficient of every surveying line were obtained.The method is divided into two steps.Firstly,based on the adjustment principle the coefficients of 5 cross-coupling monitors of every surveying line are modified at junction points.Secondly,cross-coupling correction is calculated using the new coefficients.Experimental results show that the new coefficients can compensate the influences made by the differences between actual dynamic surveying-conditions and tentative surveying-conditions designed by meter factory for calculating cross-coupling coefficients,and can obtain better cross-coupling correction.The data accuracy of marine gravity surveying can be improved with the method proposed.
To meet the requirements during project of sub-sea long-distance pipe-jacking at Shantou,an automatic surveying system with independent intellectual property right was proposed and implemented,which is suitable for super long-distance pipe-jacking project.The whole surveying during project is run automatically under control of computer without manual intervention.If there are three total stations in this system,it is able to finish a complete surveying in 3 minutes.The precision of this system is centimeter-level.The successful application of this system and perfect completion of the project of long-distance pipe-jacking at Shantou indicate that this system has advantages of high reliabilities,stable operation,rapid response,and high accuracy.
A method for fast pavement ruts detection and system calibration with laser triangulation was proposed and implemented on a vehicle-borne road laser rut-meter.For real-time ruts measuring and satisfyingly dense road profiling,the global and local thresholds were applied and the local maxim grade values and neighbor gray values were calculated to detect and extract laser lines.A method of calibration modal creation based on a Delaunay triangulation was proposed to backproject the world coordinates of laser points.Manual rut measurements and auto rut measurements utilizing the proposed method were carried out on selected road segment,respectively.The results show the auto measurements consist with the manual measurements,and the proposed method is reliable for pavement ruts measurement.
We discuss the principle of condition numbers that used for evaluating the extent of ill-posed problem of normal matrix.There is a contradiction between the stability of solution and the condition number of resection in photogrammetry.We find that it is not suitable in all cases to evaluate the extent of ill-posed problem by condition numbers.Three types of possible risks for evaluation of ill-condition extent with condition numbers were addressed in detail.Removing of outliers and re-parameterization are the prerequisites for evaluation of ill-condition extent with condition numbers.There are two effects of re-parameterization for ill-posed problems.One is improving the problem of ill-condition caused by numerical computation,and the other is avoiding the risk of using norm to evaluate the extent of ill-condition.Results of simulated experiments show that the proposed approach is validate for improving the problem of ill-condition.
Remote sensing image segmentation is an important procedure of object-oriented information extraction of high-resolution.The mean shift segmentation algorithm has been applied to many segmentation procedures since it has good effects and perfect efficiencies.Firstly,we give the principle of mean shift segmentation.Then,we present the method to improve the segmentation algorithm and implement a multi-scale segmentation.Finally,the algorithm was evaluated on the basis of experimental comparison and analysis.The results confirm feasibilities of the mean shift segmentation algorithm.
We develop an originally experiential methodology to retrieve bare soil moisture by synthetic aperture radar(SAR).The model does not require any field measurements to support,and only requires the two different kinds of polarized backscattering coefficient data.Taking into account both of the roughness parameters RMS S and the correlative length L,we combine the two roughness parameters and introduce a new roughness parameter(Rs=S3/L2)into this model.Hence,the unknown parameter in the model reduces to Rs and the volume of soil water content mv.Then,the ground soil moisture can be retrieved by integrating the equations of VV and VH polarization.The simulating data was used to validate the accuracy of this model.The result shows that there is a strong linear relationship(R2>0.71)when the incidence angle is not very small(θ0>20°).The inversion model can get a better accuracy of soil moisture without any measurements of surface roughness.This method is especially effective in the area with complex terrain where the surface roughness is difficult to be precisely measured.
Topography has significant influence on the geometric and radiometric properties of synthetic aperture radar(SAR)images.The terrain radiometric correction(TRC)of SAR images is one critical pre-processing step for quantitatively extracting bio-and geophysical parameters from SAR data.A TRC model and its implementation flow for space-borne imaging SAR data were introduced.The correctness and effectiveness of the model and its flow were qualitatively and quantitatively evaluated through several experimentations.By comparing two kinds of effective backscattering unit area computing methods,we found the project angle based method is much more effective than the local incidence angle based method.The rationality of computing effective backscattering unit area using initial SAR geo-location model was also demonstrated.The computational results show that the computation of local incidence angle or projection angle is not sensitive to the errors of the initial geo-model applied.Thus it is not necessary to re-compute them using the refined geo-location model.
A DEM reconstruction method based on CSSM(coherent signal subspace method)is proposed for multi-frequence InSAR systems.This method transforms the correlation matrices at many frequency bins into one general correlation matrix at one focusing frequencyusing a transformation matrix(focusing matrix),then estimates the elevation using subspace projecting method.The method can provide more accurate estimation of the height even when the coregistration error reaches one pixel than previous methods.The effectiveness and robustness of the method is verified by simulated data and SIR-C real data.
The FY-3A satellite is an obit meteorological satellite which can provide the globalizational,three-dimensional,multi-spectral remote sensing images.One of the FY-3A missions is monitoring the natural disaster and the change of environment all over the world.We analyze the ability of drought monitoring using the FY-3A MERSI data.First,the art of status of FY-3A satellite is introduced and the potential ability in drought monitoring is discussed.Second,the FY-3A MERSI and MODIS data are preprocessed and analysed.Finally,the relativel precision between the results of FY-3A MERSI and MODIS data are analyzed.The results of experiment indicate that the FY-3A MERSI data can improve the drought monitoring ability in same spatial and spectral resolution aspects.
We discussed analytical and numerical solutions of the Schrdinger Equation,which is satisfied by the propagator P(b,a).We introduced definition of I-Type and II-Type Schrdinger transformation of image and explained their meaning and nature of transformation.Properties of Schrdinger transform was given.High and low pass filters based on Schrdinger transformation of image were obtained.Image smoothing,edge detect and image enchancement were implemented.
Remote sensing information services classification ontology is a basic component for description,management,querying and searching of remote sensing information services on a semantic level in distributed Web environment.How to build the classification ontology is an important problem.We first analyze domain features of remote sensing information services and event-noun characteristic of their concepts.Based on that,we combine frame semantics theory to analyze semantic features of service concepts,and present an approach based on event frame and formal concept analysis to build the classification ontology.Experimental results show that this method is effective.
As the important content and main technological mean of grid,Web Services can be used to integrate and share data and models in the distributed environment.We propose a standard of registration and distribution,and an encapsulation method for GIS Services.Moreover,the mechanism of error processing is proposed in the steps of accessing Web Services,and the GIS resources can be integrated and shared more effectively.
With the development of marine science,Web Services,and gird technology,we firstly the application requirement of the sea flow field remote visualizations.The logic structure and implementation method of sea flow field remote visualizations are proposed based on Web Services and grid technology.Secondly,a prototype system of sea flow field remote visualization application grid platform was build based on the ArcGIS Server.Finally,feasibility and practicality of the proposed technical solution are proved.
Constructing virtual natural environment is a key technology to virtual geographic environment.We analyze forest environment components,and discuss the methods of modeling and visualization of forest environment element.We assure that the virtual forest fire fighting environment is made of terrain,tree,forest fire and fight tools.Based on HLA/RTI protocol,a distributed virtual forest fire fighting environment prototype is designed and implemented.The 3D virtual forest fire fighting environment is generated by the prototype system.The bottom communication layer,the framework of model control layer and 3D graphics rendering are separated to form an independent module in the system,which made the system scalable and reusable.
Network geography information systems,such as digital Earth,are getting more popular and offering geography navigation services for data requests of large-scale and high intensity.Hotmap is designed for Microsoft Virtual Earth by Microsoft Research to analyze the access distribution of spatial data.For the first time,Hotmap understands the request distribution of image data as power-law.However,Hotmap does not characterize the details.Through statistical analysis of four GlobeSIGht server logs with different granularity of times,the Zipf-like distribution(one of power-law)for image tile requests is found.Image data has a heavy skewed access,which means hotspot data exist and 20%(5%)of tiles pull nearly 80%(50%)requests.This finding helps the design and optimization of digital Earth system,for example,in aspects of image data storage declusting and distributed cache.
Laneway is one of the principal parts in geological virtual scenes.A hierarchical modeling method for plane connected laneway entity based on media curves was proposed.Node-path graph according to the broken up curves generated by intersection points of media curves was constructed.All closed loops were picked up through outer path tracing prior principle.The cross-section data of media curves were obtained,and a series of hierarchical contours were built,which compose the hierarchical contours of the laneway after offset calculation and connection of boundary path.Finally,triangular grids of laneway were generated by 3D objects reconstruction of adjacent contours and triangulation for both roof contour and bottom contour.The results show that topology of the vertexes and paths was used to reduce calculation burden,simplify implementati
High accuracy surface modelling(HASM)constructed based on the fundamental theorem of surfaces is more accurate than the classical methods.But HASM must solve a big sparse linear systems.Gauss-Seidel(GS)can be considered as the first method for solving the linear systems.In order to decrease the computation costs and improve the accuracy of HASM,we employed a modified Gauss-Seidel(HASM-MGS)to solve the linear systems of HASM.Gauss synthetic surface was selected as the research object.We proved that HASM-MGS is more accurate than HASM-GS and the classical methods used in Matlab.The computation time of HASM-MGS is approximately proportional to the one power of the total number of grid cells,which can be considered as a big improvement in solving HASM systems.
We popose an efficient algorithm for complex polygon clipping by adopting the trapezium segmentation technique and scan-line idea.Firstly,we find and compute the intersection points between main polygons and window polygons,then we record and sort the Y values of these points and the points in all polygons.Secondly,we cut all the polygons into some trapezium units by drawing the scan lines on the basis of these Y values and intersecting the edges of all polygons with the scan lines.Thirdly,we complete the trapezium-split operation line by line and pick up the intersection parts between the trapezia from main polygons and those from window polygons.Finally,we acquire the clipping polygons by tracing the boundary of the intersection parts.This algorithm ovecomes the complex computations such as the line reorganization and calculation of entry and exit points on the polygons.
All existing spatial clustering methods only utilize the spatial distances and the numbers of entities in the spatial nearest neighborhood to find the spatial clusters in the spatial database,without taking the spatial local distribution characters into account.Hence,the clustered results are unreasonable in many cases.To overcome such limitations,we propose a new spatial clustering algorithm based upon the local distribution among the entities in certain spatial neighborhood,where median angle for each entity is employed to measure its property of local distribution.In the process of spatial clustering,a series of recursive search were implemented for all the entities so that those entities with its median angle being very similar are clustered.Two tests were implemented to demonstrate that the proposed method is more prominent than DBSCAN,and can be used to find the clusters with arbitrary shapes.