2013 Vol. 38, No. 4
Abstract: The harmonic constants of 170 tidal constituents at Zhongshan Station, East Antarctic are obtained from the tide data lasting from Feb. 2000 to Oct. 2005 using classic harmonic analysis method. Chi\|square test is applied to the residual, which demonstrates the disadvantage of the classic harmonic analysis.A higher interval of the tide data or a longer period of data is suggested to be adopted to improve the distinguishability of tidal constituents. Results of the harmonic analysis show that the tide type of Zhongshan Station isirregular diurnal tide. The main tidal characteristic value and engineering water level are also calculated.
Single, fixed and dynamic methods of crossover analysis are compared, and dynamic outperforms the others. The spatial distribution of elevation change from Zhongshan Station to Dome A is estimated during October 2002 to September 2007. Backscattered power is an important factor to derive elevation change. The adjusted height change over the study area is in whole balance but unevenly distributed. The positive increase is shown in Enderby Land, which agrees with ICESat.
The requirement of observation precision of pulsar astrometric parameters including the position, proper motion and parallax by VLBI technique is analyzed based on the fundamental principle of pulse timing observations and the application in deep space navigation of millisecond pulsars. It is also discussed concerning the current technical specifications, the deficiencies as well as the possible ways of improvement in the equipment of electronic backend of antennas, the data cross-correlation processing and the time synchronization of the Chinese VLBI network on the observation of millisecond pulsars for criticism and reference.
The power spectrum and the free air gravity anomaly of different gravity field models CEGM02, SGM100h, SGM150, LP150Q, GLGM\|3, LPE200 were analyzed. The orbits of the lunar exploration spacecrafts with different altitudes and inclinations were simulated for all the gravity fields. Results firstly show that all the models behave the same way for polar orbit satellites, which reveal that all the models can be recommended in precision orbit determination for the polar orbit satellites. But CEGM02, SGM100h and SGM150 contribute more to those non-polar orbit spacecrafts. It is accordingly suggested that those non-polar orbit spacecrafts could be launched for future lunar exploration so as to perfect the lunar gravity field model. Moreover, the lunar gravity field model will be refined by using localized spherical harmonic functions which can efficiently extract local gravity field signals.
By processing GPS data of the fiducial stations and repeatedly observed stations from 1998 to 2009, the corresponding velocities of a set of 1 041 reference frame stations (RS) are obtained, constrained to the current frame of 2000 Chinese Geodetic Coordinate System (CGCS2000). To establish the velocity field of horizontal crustal movement of Chinese mainland by using hardy multi-quadric fitting model and the velocities of 1 041 RS, we discuss the key problems of the hardy function interpolation: the influences of kernel function, nodes and smoothing factor. And we establish a largely covered and valuable speed field model of horizontal crustal movement of Chinese mainland using hardy function interpolation. This established speed field result would be widely used for maintaining 2000 Chinese Terrestrial Reference Frame (CTRF2000) and researching the crustal movement of Chinese mainland.
There often encounter ill-conditioned problem of navigation constellation for autonomous orbit determination by using the inter-satellite link, so orbit determination of constellation can not be achieved directly using EKF algorithm. For distributed autonomous orbit determination model, the divergent reasons of EKF algorithm are analyzed through the thought of biased estimation. Thus the ridge-type EKF algorithm is first proposed by using the combination of ridge estimate and EKF algorithm, and a specific method is given for the determination of ridge parameter. Finally, Walker24/3/1 constellation is simulated by STK and distributed autonomous orbit determination is implemented. The validity of ridge-type EKF algorithm is verified by the results of simulation example.
We developed a new method of single-frequency precise positioning for the users in a large region. Compared with current methods, this new method avoids selecting designated static reference network, it has been proved to be effectively modeled on the ground instead of be modeled at 350 km above the ground (as is shown by SEID), and the calculation of the maximum-modeling difference is also given. The results show that for an ionosphere\|active region of 100 km×100 km, where there are at least 3 dynamic reference stations, user can get cm-level position accuracy in the horizontal direction with 20 minutes observation data. Furthermore, this method provides a new way on the research of single-frequency precise positioning.
The Ionosphere is a complex system, and of which total electron content (TEC) is a representative parameters. For its non\|linear and non\|stationary characteristics, the empirical mode decomposition (EMD) method is proposed for data processing in this field. And the data decomposed with EMD are used to do time series analysis and predict TEC value.Prediction and comparison experiment is carried out with the data provided by IGS in 2010. And the results show that the mean relative precision of TEC predicted within 5 days is 92.25% by the proposed method , while it is 89% by the single time series analysis.
In order to fill the data gaps in the voxels which were not intersected by any rays and depend on the initialized information, a new ionospheric tomography algorithm with smoothing method was proposed using the continuity and smoothness between the neighbor voxels in the tomography based on the multiplicative algebraic reconstruction techniques. Using the high precise dual\|frequency ground\|based GPS observation from the crustal movement observation network of China, the ionosphere density was reconstructed over China by the new technique. The retrieved ionosphere delay by the inversed result was compared with that from test stations, and the obtained density profile was compared with the ionosondes. The results demonstrated the efficiency and reliability of the new method.
The original data of the GPS stations in the Crustal Movement Observation Network of China was processed. We adopted two different data processing methods differ in choosing reference coordinators to process the data. Part of ITRF stations which are superior in stability were selected in the first method and the ITRF stations in the neighborhood were selected in the second. Comparison of the result through processing the data relatively, systematic deviations have been found between the two results. The reulsts show that the magnitude and characteristics of the systematic deviations act differently in different directions, and the functional mechanism is relative to the spatial and temporal distribution of the sites. Through analysis on the phenomena and findings refered, some relative conclusions are derived and the advices on establishment of regional coordinate system are also given.
Spirit leveling observations, together with engineering geological data are employed to determine the source parameters of active faults and ground fissures in the Qingxu region using two double dislocation fault models. The optimal model suggests that: ① the relationship between active faults and ground fissures in the study region appear to be a “Y” pattern. ② The present rifting velocities of ground fissures are up to 15.1 mm\5a-1, greater than their corresponding dip slips. ③ The lower boundary of ground fissures is at depths of around 380 m. ④ The dip\|slip rates of ground fissures are greater than those of active faults (1.6 mm\5a-1). The results are consistent with hydrological and geophysical data.
Hydrological processes cause variation in gravitational potential and surface deformations,both of which are detectable using space geodetic techniques. We computed surface vertical displacements due to inland water storage changes using GRACE time-variable gravity field for GORS sites in Shanxi province, during from May 2009 to Dec. 2010, and compared the results with GPS height residuals during the same period. The results demonstrate that variations of hydrological surface deformation derived from GRACE and GPS height residual time series, for most CORS sites, are both about ±6.0 mm. The average amplitudes of annual signal extracted from GRACE and GPS are both about 2.5 mm, however, the phase discrepency is large. Since no corrections were applied for diurnal and semi-diurnal atmospheric loading, high order ionosphere, and non-tidal ocean loading, which would propagate into site coordinates time series and affect GPS annual signals. Therefor, we believe that the disagreement between GRACE and GPS is more due to errors in the GPS data processing.
A shadow compensation method for aerial images is proposed. First, an image segmentation method is applied and the threshold value is calculated to help predict a shadow region. Then the ratio of direct light to ambient light pertaining to the shadow region is calculated. In the meantime, the multi-band blending method is adopted to realize a smooth transition from shadow region to non-shadow region. Finally, the shadow compensation is finished according to a certain illumination model. The experiments show that the proposed method can not only effectively compensate the shadow regions, but ensure a smooth transition from shadow to non-shadow regions.
For moon rover navigation and exploration mission during the 2nd stage of Chang’e project, high-resolution images are necessary. So a moon rover image super-resolution reconstruction algorithm via using compressed sensing was presented. The target is to reconstruct an original image from its blurred and down-scaled noisy version. The algorithm assumed a local Sparse-Land model on image patches, serving as regularization. The images from Apollo Project, tests in the 2nd stage of Chang’e project and natural image database were used in extracting patches for building two dictionaries. The K-SVD algorithm was used in training the dictionaries. Then the effective segmentation was implemented on low-resolution image. Through solving optimization problem via orthogonal matching pursuit algorithm, the sparse representation for each low-resolution image patch with respect to Al was obtained, and the representation coefficients were applied to Ah in order to generate the corresponding high-resolution image patch. At the end of experiment the high-resolution image which satisfied the reconstruction constraint was achieved by using least squares algorithm. Numerical experiments about moon rover images from tests in the 2nd stage of Chang’e project demonstrated the effectiveness of the proposed algorithm. Moreover, the proposed algorithm outperforms bicubic interpolation based method and the algorithm via Yang in terms of visual quality and the peak signal to noise ratio.
Hyperspectral data contained over hundreds of narrow contiguous wavelength bands are extremely suitable for target detection due to their high spectral resolution. In the target detection for hyperspectral image, the background data are not well represented from the original data sources. We propose a weighted hyperspectral image target detection algorithm based on independent component analysis orthogonal subspace projection(ICA\|OSP). The methods start from a collection of independent component of the image pixels, through a spectral similarity measure weighted so that each pixel to give the appropriate weights. It can effectively solve the problems that can not correctly extract the background data from the original image. The problem usually causes a higher false alarm probability. AVIRIS hyperspectral image simulation and detection algorithms are compared by ROC curves with the relevant target detection algorithm, and the results show that the proposed algorithm can reduce the false alarm probability, to better target detection effects.
An objective method for performance evaluation of edge detectors was proposed based on image reconstruction. Firstly, binary edge maps were extracted by testing edge detectors. Then, combining the location information and brightness information in edge support region, image was reconstructed using enhance inverse of the distance for the weighted average of image pixel values in divisional regions. Finally, performance of edge detectors was evaluated using integrated index which represents feature similarity between reconstructed image and original image. The experimental results show that the proposed method is consonant with subjective judgment and has practical implementation.
The existing segmentation methods mostly directly use backscatter coefficient images or span images for segmentation, or a certain kind of polarization characteristic images, and do not make full use of the polarimetric characteristics and spatial characteristics. We propose a buildings segmentation model based on PolSAR images, which makes full use of the polarimetric characteristics and spatial characteristics of buildings by FNEA (fractal network evolutionary algorithm) and MLR (multiple linear regression) model. Using the proposed model to achieve the segmentation of the L\|band EMISAR airborne images in Foulum area. The experimental results show that the segmentation model is feasible.
Considering the low efficency and mismatching in SIFT\|based multi\|source remote sensing image registration, we improve the SIFT algorithm through two aspects of point feature extraction and point feature matching. Firstly, we acquire an appropriate number of well-distributed point features by controlling their number and distribution. Secondly, an optimized strategy is adopted to realize a coarse\|to\|fine feature point matching approach by applying the initial affine matching, precise matching and mismatching elimination processes. Experiments on several multi\|source data sets show that the proposed algorithm performs better than the SIFT algorithm on both efficiency and accuracy.
To solve the mis-clusters caused by the traditional information cut (IC) algorithm when it is applied to segment images with gray changes, a modified information cut in wavelet domain (W-MIC) algorithm is proposed. First, it modifies IC using a new Parzen windowing which combines the gray relevance and space relevance between image pixels in order to reduce the effect of gray changes to image segmentation. Further, considering the difficulties of selecting the optimal parameter in the above modified information cut (MIC), MIC is introduced to wavelet domain to reduce the complexity of parameter selection via the smoothing role of wavelet. Remote sensing image segmentation results demonstrate that it effectively decreases the influence of parameters selection, and it can not only avoid the mis\|clusters caused by gray changes, but also keep image edges.
According to the application demands, we divide geographical areas into four kinds. They are densest area, dense area, moderate dense area and sparse area. Aiming at different areas, the multi-scale display models are built to adapt their characters. Then, automatic estimation methods of different density areas based on RGB value are studied. On the basis of qualitative analysis and survey statistic, a hierarchical basic geographical elements display system is built. At last, taking examples of electronic maps of the area of mid-China, multi-scale display experiments are carried out.
A method of vectorization of scanning map based on Voronoi diagrams was described. It traced pixel（grid units） of boundaries of map elements by contour tracing technology based on black and white binaryzation for image in some layer of scanning map, and extracted end of segments on boundaries by scanning endpoints. Then according to the basic points getting from pretreatment, constructed Voronoi diagram. Finally, described the decision rule of skeleton according to the numbering mechanism and the storage structure of Voronoi, finished vectorization through extracting skeletons from the set of edges of Voronoi according decision rule of skeleton. The experiments show that the method proposed could well process more complex scanning map, supply the actual demand in rate and accuracy.
We propose a method for multi-scale representation of curve which keeps topological relationship unchanged and elaborates the process of progressive transmission of curve data over the Internet based on this method. Firstly, the importance degree of nodes and the information about public constrain points and monotone chains are stored in a monotonous linear BLG tree structure. Then the multi-scale curve is generated in real time based on this structure and the topological relationship is maintained by an optimized monotone chains intersection algorithm. Finally, the method was used in the experiment of progressive transmission of curve data over the Internet and verified its effectiveness.
To preserve topographic feature during simplifying of contour line groups, a progressive simplification method is proposed. Firstly, topographic feature points and lines are extracted from contour lines according to expert rules. Secondly, both the extracted topographic feature points and lines as constraints are quantified as control variables. Based on the progressive graphics simplification approach, the non-feature points, feature points, feature lines and its associated bends on the contour lines are selected or deleted progressively according to the value of control variables so as to realize simplification of contour line groups with intelligence. Experimental results show that the proposed methods can effectively preserve topographic structural feature and improve the intelligence during contour line simplification.
Settlement matching is one of the kernel parts of multi-source spatial data fusion and multi-scale data updating. Following the cognition habits of mankind in finding strange buildings, the spatial relationship similarity is used to assist the settlement matching process. The discrete computing method according with human cognitive habits is proposed after analyzed the similarity of topological relationship, distance relationship and direction relationship. And the matching processes are as fellows. Firstly, the outstanding settlement of the original object is picked up and computed to find its matching object. Secondly, referencing the matched object, the next matching object is achieved by the extend-first traversal to unmatched objects. Thirdly, the precision matching is fulfilled by traversing every settlement object all in this way. Finally, the matching quality is evaluated by comparing the spatial relationship similarity of adjacent objects. Test illustrates that this method can effectively improve the matching precision in the case of data hardly displacement and high settlement shape homogeneity.
A geographic ontology fusion method based on granular theory is presented. First, Formal concept analysis (FCA) is used to formalize different geographic domain ontologies. Then granular computing is introduced to geo\|ontologies fusion to implement concept lattice reduction in different granulations. Finally, experiments are conducted by combing fundamental geographic information data and spatial data in the hydraulic engineering domain. The results show that Geo\|ontologies fusion is a progressive process, and the proposed method is valid in multi\|source Geo\|ontologies fusion. As well as merits and limitations are discussed.
An information system of land consolidation projects management (LCPM) based on the workflow model and business ontology is designed to solve the problem of that traditional information systems can′t handle the complicated data and business of land consolidation projects simultaneously. The business ontology is established on the basis of related official documents of management measures and expert knowledge, and it is regarded as the metamodel of the workflow model of LCPM which can make the integration of workflow and dataflow, and satisfy the uncertainty of business of LCPM. Functional modules of the system with weak coupling and strong polymerization are designed in accordance with the workflow model of LCPM, and the software development pattern of plug-in framework is adopted to realize the system on computer. At last, taking the Guangxi Zhuang Autonomous Region as a case study, we find that the design of Information system of LCPM presented above is effective and feasible.
A constrained fuzzy cellular automata model was established to simulate the spatial regulation boundary of urban land expansion. In the model, theories of variable weight and fuzzy set, area constraint and spatial constraint were introduced. A case study was taken in Taicang city by using this model. The results show that urban land expand by the means of inner-fill firstly, and then expand outward, and it is a type of compact development. The urban expansion direction accords with requirement of the eleventh five-year planning. We find that this model could be used not only to solve the problems of rational scale of urban land, but also to deal with problems of different factors′ influences on land development and fuzzy decision in spatial location flexibly. So the model could satisfy the current needs of land use planning.