2010 Vol. 35, No. 9
We estimate the length of day(LOD) from VLBI observations during 2008-01-2009-03, and analyze its precision. And the estimated results are compared with the results from IVS. Then, the length of the month and half-month periods of the changes of LOD is computed. At the same time, the curve map is made with 2001-2009 VLBI observations to analyze the periods of Earth rotation, with which the seasonal changes is presented and analyzed. At last, the factors that possibly cause the changes of LOD are analyzed.
We propose an autonomous navigation scheme based on optical navigation and inertial measurement unit(IMU) for lunar soft landing. In order to remove the accumulation errors of IMU, we use the on-board optical measurement information of pre-selected feature point to obtain relative position of the probe. Then, based on those optical information and the output trajectory of IMU navigation, the amendments of IMU navigation are completed by the multi-model adaptive filtering. In addition, the observability of entire navigation system is analyzed. Finally, the feasibility of the proposed autonomous navigation scheme is confirmed by numerical simulation.
We study the characteristic of global mean atmosphere pressure, and point out the shortcoming of traditional inverse barometer (IB) correction of satellite altimetry. Then, three kinds of inverse barometer corrections are compared in detail based on T/P altimeter data. Compared to the constant referenced IB and global mean value referenced IB, the DAC model based IB correction which high frequency signal is considered shows best, which can reduce the RMS of crossover difference 5.70 mm, and improve the fitting mean square error in sea level change 18% and 12% relative to the constant referenced IB corrected SSH and global mean value referenced IB corrected one, respectively.
To solve the estimation problem of ionospheric delay corrections within satellite-based augmentation system(SBAS), an estimation method, which use the Kalman filter to estimate ionospheric delay of the navigation signals, is proposed. The ionospheric vertical delay and related change rate of the ionospheric grid points are estimated simultaneously. The system model is established on the basis of the slow-variant character and the measurement model is constructed on the basis of the grid model involved in the SBAS. The relevant analysis is conducted by the simulation method. The results indicate that comparing with the traditional ionospheric correcting method,this method can estimate the realtime ionospheric corrections with enough accuracy and can be an available for calculating the ionospheric differenced corrections in the SBAS.
Tall buildings are very sensitive to wind. We demonstrate that high-rate GPS single epoch positioning technology is effective in measuring wind-induced vibration of tall buildings by analyzing simulation vibration test and field measurement data. After application of wavelet decomposition and reconstruction, 2-mm vibration deformation of tall buildings can be extracted precisely from the GPS time history solution.
The convergence speed of Kalman filter is slow and the accuracy of initialization is low if the ambiguities are taken parameters estimated in dynamic precise point positioning. The accuracy of Kalman filter will degrade if the spectral density of the dynamic model is not accurate. So fixing single difference ambiguities are used to improve the speed of convergence. Firstly, the ambiguities of ionosphere-free observations are estimated with the sequential least squares, and the ambiguities of wide lane are fixed. Then, the ambiguities of narrow lane are fixed. At last, the ambiguities of ionosphere-free observations are fixed. For errors of the spectral density affect covariance matrix of the predicted state vector, adaptive filtering is used to control outliers. Adaptive factor on the basis of current information can adjust the scale between covariance matrix of predicted state and covariance matrix of observations noise, so that the contribution of dynamic state to results of Kalman filter is more efficient. In the processing of data of air, the adaptive Kalman filter in which single difference ambiguities fixing are used, can improve the speed of convergence and accuracy of positioning. The stability of adaptive Kalman filter is better when the spectral density has different numerical value.
Velocity determination of kinematic vehicle is important. Low-cost GPS receiver can only measure the pseudoranges and the carrier phase without the Doppler measurements. A new method for velocity determination by derived pseudoranges is presented. The formulas of derived pseudoranges are given and the precision of the velocity is analyzed. This method is applied to two actual experiments of aircraft and vehicle applications. Experimental results shown that the precision of vehicle application is lower than that of aircraft application. The influence of derived epochs number on the precision of velocity is different based on different environments, receivers and dynamic states. And the character of the receiver also takes great influence on the precision of velocity.
City spatial data acquisition is the key to digital city. In allusion to the limits of traditional differential positioning model with 3DSurs, and with the development of regional continuous operational reference system or stations (CORS), 3DSurs precise positioning technique based on CORS is put forward. Firstly, we compute the approximate coordinate of 3DSurs. Then, we calculate the synthetical error correction of 3DSurs from CORS. At last, we calculate its coordinate precisely based on the front two steps. Taking the data from QDCORS for example to analyze the positioning precision of 3DSurs based on CORS, we find that the positioning precision is prior to 10 cm, and it can meet the need of city spatial data acquisition and positioning.
We present the theory of marine magnetic gradiometer survey and the characteristic of wavelet. Based on the wavelet analysis, a method for detecting high frequency magnetic disturbance from the marine magnetic gradiometer data is put forward. The results of data analysis of the test show that the method is effective in interpreting and detecting the high frequency magnetic disturbances which exist in the marine magnetic gradiometer data, even if the magnetic anomaly is small. This method is useful to improve the capability of magnetic detection in the marine magnetic gradiometer survey.
In terms of the attitude correction of the sensors position in hydrographic survey, determination of the barycenter of the surveying boat accurately is necessary. Based on the RTK technique, a new method for determination of the barycenter of the surveying boat is presented and a series model is developed under static state. The simulated results show the calculations and the true values are in a good consistency. The validation and reliability of the new developed approach is verified. The error of the barycenter position of the surveying boat determined by the observation including RTK noise level can also be neglected.
To meet the need of model development and assimilation development,we design a brightness temperature simulation system based on radiative transfer model, which combine the characteristics of atmosphere, land surface and the sensor. We use the model directly in satellite data assimilation system(SDAS) to correct its static parameters and improve the understanding. The errors structure analysis is performed on errors introduced by topography,atmosphere,uncertainties in the parameterizations of the forward model.
We proposed a novel algorithm for lightning location on oblate Earth surface. This grid-search based method is carried out overall coverage area of the network to find the most probable position of a flash. The solution of this method can rapidly approach ultimate location when multi-level gird search method is adopted. This meehod needs no initial solution, and in practice can be used to provide the initial solution for iterative algorithm. The validity and stability of the proposed method is confirmed by computer generated data and practical transmission-line lightning faults data of lightning location system for power industry.
We introduce parallel computing to provide high performance computing and enough computing resources for massive remote sensing data processing. Based on Condor and SNAPHU(statistical-cost, network-flow algorithm for phase unwrapping), we build a parallel computing environment in cluster system for phase unwrapping. We analyze processing results in aspects of unwrapping accuracy, memory usage and computing efficiency, and conclude influencing factors in the three aspects. The experiment shows that parallel computing effectively solve the computing problem occurred in massive remote sensing data processing, such as memory shortage and inefficient computation.
Based on intensive analysis of the relationship between interferometric coherence and Doppler frequency difference, we propose an algorithm for spaceborne interferometric SAR signal processing with coherence optimization. Different from those traditional SAR processing algorithms, the basic idea of this algorithm is the Doppler parameters in SAR signal processing should be equalized for interferometry. Although signal-noise-ratio (SNR) may be lowered, the coherence between the two SAR images can be improved. Therefore, interferograms with better quality can be acquired by employing the proposed method. The level 0 and level 1 products of ERS-1/2 Tandem datasets in Zhangbei has been tested. The results show that the quality of interferogram from level 0 data processed with the proposed method is better than that from standard level 1 data provided by ESA. The experimental results indicate the proposed method is highly desirable for research and application for InSAR technology.
For the two commonly used orho-rectification models in spaceborne SAR, which are collinearity model and range-Doppler (R-D) model, we proposed an analysis for the common and opposite characteristics existing in their principle and solving steps in sequence. Moreover, we made a comparison for the computation result based on the on-site experiment data obtained by corner reflectors as well. Experimental results illustrate that although the two models should not only be based on entirely different principles of hypothesis, but also own different computation results with the same internal physical parameters, the output accuracy of the two models are basically the same.
Since the inadequate use of statistical information in the multiscale Markov random field model in the wavelet domain, the fuzzy theory is introduced into the model and a new multiscale fuzzy Markov random field model in the wavelet domain is presented. Firstly, the model which is based on the fuzzy theory defines a fuzzy probability field, which is used to describe the degree of every pixel belong to which segmentation region in each scale in wavelet domain. During evaluating parameters stage of the following feature field, the whole pixels' features in the same scale are taken into account. Then, the indicator field which reflects the energy of every pixel that belong to certain segmentation region is induced from the feature field. Finally, a three-step interaction iterative segmentation steps based on the Bayes rule is induced. The experiments compared with the ICM and MRMRF algorithms have proved the proposed method’s availability
Road extraction from high-resolution remote sensing images has very important significance for improving the informatization admministration level of planning, road network maintaining and navigation and traffic analyzing. Bertrand curve property is discretized, and is used to extract the road edge information from high-resolution remote sensing images. The proposed algorithm can effectively eliminate non-road edge, at the same time it can interpolate the companion line of road edge, which makes the road edge more continuous and integrated. The experiments and quantitative assessment results indicate that in comparison with the classic edge detection operators the proposed approach is more efficient.
Amplitude data are the key data for generating backscatter intensity maps as well as seabed sediment classification. There are noises in signals because of the system itself or some other factors when the amplitude data are obtained. The existence of these noises directly effects data processing, which makes seabed backscatter strength map distorted. So the amplitude de-noising becomes very important. Spatial filtering methods in the image processing are referred to. By comparison and analysis with the actual observations, we prove that the gradient inverse weight smoothing algorithm is optimal, and the experimental results show the correctness of the conclusions.
Atmospheric aerosol optical depth change has great influence on the accuracy of Earth observation, and is one of the research hotspots of quantitative remote sensing. However, traditional atmospheric radiative transfer softwares such as 6S and MODTRAN choose horizontal meteorological visibility as the key optical property parameters of aerosol. Hence, thorough discussion of the relationship between aerosol optical depth and horizontal meteorological visibility has important practical significance. Four convert models are validated by measurements of horizontal meteorological visibility and synchronous AOD of MODIS. Results show that Peterson model with atmosphere scale height H can obtain higher accuracy.
Location-specific space-time accessibility based on time geography framework is proposed, which has the ability of reflecting the relative accessibility between specific location and the whole region, and incorporating the constraint of available activity time of point of interest. This approach has implemented the personalized representation of accessibility by integrating the activity requirements, such as total activity time, available activity time and interesting activity opportunities. The method is helpful for individuals to explore their space-time accessibility for further activity decisions.
The most confidential information of remote sensing images is related to military security and political stability, and confidential information of the regional data need to beencrypted to protect itself. On the basis of analyzing the characteristics of large quantity of remote sensing data and application requirements on security, a scheme of authorizing the use of remote sensing images based on multi-level secrurity is put forward. The same remote sensing images after encryption are distrtbuted to different level users, such as authorized user, partly authorized user, unauthorized user, but different authorization users acquire different importmant degree information after decryption through their own decryption keys. The scheme has high confidentiality and high computing efficiency encryption algorithm, and solve the difficult problems of large quantity of remote sensing data on security and secrecy.
For the characteristics of digital watermarking of vector spatial data, the DFT(discrete Fourier transform) blind watermarking model is put forward based on QIM(quantized index modulation) idea. Firstly, DFT is done to vector spatial data. The watermark data are embedded in the magnitude of DFT through quantification. Then, through inverse DFT transform, the embedded vector spatial data is obtained. Finally, the confirmation is done with text format's vector spatial data. The results show that the watermark has good availability, not visibility, as well as has good robustness to format conversion, data translation, rotation.
We discuss the necessity and importance of evolving from the quality of geospatial data to the quality of geospatial information services. After analyzing the definition and connotation of quality and service, we propose a reference model of quality of geospatial information services including basic conceptions, roles and activities.
Based on analyzing the characteristics of real-time traffic information (RTTI) and navigation data model, we point out the difficulties to express RTTI in hierarchical road network. We focus on the fusion method for RTTI and hierarchical road network. Firstly, the relationship between RTTI and logical road network is established by RTIC. Then, we propose the fusion method based on the relationship of multi-link in the upper and lower layer. Lastly, the results demonstrate that the method achieves multi-scale representation of real traffic map in mobile terminal and meet the requirement of dynamic navigation.
For the purpose of urban management, many spatial boundaries of urban areas such as administration boundaries, postal zones, urban planning zones, traffic analysis zones were designed by different departments for specific purposes, thus results in incompatible boundaries. The social statistics data based on these zones are difficult to use by other departments due to these incompatible spatial boundaries. The urban basic grid is proposed, and the division principle is detailed. An algorithm based on hierarchical spatial reasoning is designed to delineate the urban basic grid. An experiment is done to delineate the urban basic grid. The results indicate that the urban basic grid can be used to aggregate to higher level urban grid, and thus that the social statistics data collected by the urban basic grid can be shared among other departments.
Updates propagation is the process of using updating information of the changed features in the new version of fundamental geographic database (FGDB) to perform updating operations such as revision, addition, deletion on the corresponding features and their relates data in client database (CDB) for keep it also having good currency. At present, updates propagation is often implemented manually, needs too much human-computer interaction and is time-taking, laborious and error-prone. In order to automatically and effectively propagate updates from FGDB to CDB, four basic operations necessary for updates propagation, schema matching, change extraction, entity identification and updates integration, are respectively discussed and analyzed aiming to its basic implementation requirements and the influences of semantic heterogeneity on it. The automated execution approaches to these four operations are comparatively analyzed and evaluated. These studies are helpful to grasp the concepts, the implementation requirements, the difficulties, the solutions of updates propagation and the key problems needed to be further researched, and provide the necessary research foundations for designing and developing the automated execution algorithms and the software tool.
We put forward a new method for buffer generation based on run-length encoding system and raster overlay idea. Firstly, we use a brush whose width equals to the buffer distance to scan and trace the buffer objects from the bottom of raster region, and label the grid which has been scanned and execute the dynamic raster overlay to get the buffer zone in the raster form. Then, we transform the raster data into vector. Considering the obvious deficiency of computational efficiency and memory capability for rater data based on direct encoding, we adopt the run-length encoding method to store the raster data and perform the raster operations based the data structure. In order to enhance the spatial location precision, we suggest to use the float-type data as the mark of edge for run-length unit. Taking the set of linear objects for example, we illuminate the implement steps to generate the buffer zone using the overlay algorithm of run-length brush. The tests and analysis indicate that this method is a fine buffer generation algorithm, which has a general advantage in the time and space complexity and computational precision.
An optimized producing environment is a key issue in bio-chemical industry production. Due to the complex mechanism of bio-chemical production, understanding the favorable environment is very difficult. On the other hand, a great amount of data has been accumulated through industry production over years. It is possible to find out valuable rules that may contribute to the improvement of production efficiency and quality through data mining and association rule mining. We proposed the concept of association rule mining with fixed decision items. The corresponding mining algorithm was introduced and the application was illustrated. The algorithm was based on the traditional Aprori and, due to an advanced pruning strategy was adopted, it showed much higher efficiency.
Land consolidation districting is vital and pivotal for the land exploitation and consolidation planning. At present, the main measures, including overlaying method, dominant sign method and constellation clustering method, have several essential defects, such as lacking maneuverability, low automatization and high influenced by artificial experience. In fact, because of holding a set of canonical principles and restrictions, land consolidation districting is essentially a kind of multi-objective spatial districting problem, which can be automatically resolved by the multi-objective optimization model. So, we put up a MOTS (multi-objective tabu search) algorithm to solve the problem, and describe the program flow and core issues in detail. Finally, we take a case study of farmland consolidation districting in Jiaxia District of Hubei Province to exam the correctness of the model.