Table of Content

20 January 2014, Volume 43 Issue 1

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A New Method of High Precision Wavelet Packet De-noising

2014, 43(1):  13-20. 

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In the field of GPS deformation monitoring, the traditional wavelet de-noising method retains only the low frequency of useful information. It is easy to get rid of intermediate frequency and high frequency useful information. The wavelet packet analysis is a new kind of wavelet analysis method developed in recent years, which is a more subtle de-noising method for considering useful information of the various bands. The key of the wavelet packet de-noising is to select the appropriate threshold criteria and to process the wavelet packet decomposition coefficients by the threshold, but the researches using traditional wavelet packet de-noising method is not sufficient. This article is for the lack of traditional wavelet and wavelet packet analysis. According to the distribution of different signals and their noise, wavelet packet decomposition coefficients are arranged by the frequency order, and segmented in accordance with information type, to select the appropriate threshold criteria for each band and to perform threshold processing. It is the method of wavelet packet de-noising with multi-threshold criteria based on frequency order. The results show that this new method can effectively remove the noise of each band through theoretical analysis and practical applications. The de-noising ability of this method is better than the other methods such as traditional wavelet de-noising or wavelet packet de-noising. Studies have shown that this method can valid preserve the frequency 10-1 Hz magnitude of useful information from the de-noising signal after de-noising when the sampling frequency is low. Therefore, it can be widely used in the field of high-precision GPS deformation monitoring.

Evaluation and analysis of GOCE earth gravity field model in Qinghai-Tibet region

2014, 43(1):  21-29. 

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The Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission has provided several products of earth gravity field models computing by satellite gravity gradiometry (SGG) since its launch in 2009. In this paper, the precision of the GOCE gravity field models in Qinghai-Tibet area is tested by GPS-leveling and gravity anomaly data, and a new filter method is introduced as a reference in the course of gravity testing, The test results show that the medium order of GOCE models is better than other typical models in Qinghai-Tibet area. The next, the differences between GOCE-only model and the other three models are computed respectively in terms of geoid and gravity anomaly in Qinghai-Tibet region, then the spatial and the field source depth distribution which is first derived from statistic analysis method of the big difference are discussed. Based on the calculation results, some conclusions have been drawn as follows: in the horizontal direction, the obvious difference between the GOCE models and other typical models appear in the region where landform is complex such as Himalayas, Tianshan, et al; in the downwards direction, the large difference focus on the lithosphere.

Downward continuation of magnetic field with improved Taylor series

2014, 43(1):  30-36. 

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The downward continuation process is inherently unstable and any high frequency noise present in the data gets strongly magnified in the transformed map in such a way to mask any useful signal. How to accurately calculate the any order vertical derivative of total field magnetic anomaly (Bm) is a crucial matter of implementing downward continuation. In this paper, we studied the properties of harmonic function and proved that Bm is a pseudo-harmonic function. Based on the use of stable vertical derivatives, a stable algorithm was presented to perform downward continuation applying improved Taylor series approximation. Furthermore, the problem of edge effects could be settled out using grid extension to the four directions with half a cosine function before the vertical derivative calculation. The effectiveness of the suggested algorithm has been illustrated by simulated sphere/prismatic examples and real magnetic data from an airborne and seaborne magnetic survey. The conclusion shows that the presented technique can be employed to perform stable downward continuation of total field magnetic data and provide better results than other techniques based on Fast Fourier Transformation (FFT) or on normal Talor’s series or integral-iteration method when the data is noise-free, and almost the same as integral-iteration method if the data contains certain noise.

A Modified Gauss-Newton Method for Downward Continuation of Potential Field

2014, 43(1):  37-44. 

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For the ill-posed problem of potential field downward continuation, this paper proposed a novel improved iterative method based on the analysis of the basic principle and the filter characteristic of the filter function of the Gauss-Newton iterative method. This novel improved method uses an incremental geometric regularization parameter adaptive choice method and the minimal residual criterion for the iterative step choice. The comparison analysis of gravity theoretical model and real geomagnetic data shows that the proposed iterative method has high downward continuation accuracy and good convergence.

Complex Least Squares Adjustment and Its Application in Tree Height Inversion with POLInSAR Data

2014, 43(1):  45-51. 

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The surveying observations in traditional geodesy and remote sensing usually are real numbers, so the theory of surveying adjustment is based on real space. However, in modern geodesy and remote sensing, more and more observations are expressed in complex form. As same as the real number observations, the complex number observations are also facing the problem that how to identify the best estimations of unknown parameters from the observations with errors. However, data processing methods involving complex observations are mainly step-by-step or direct solver based on the observation process which cannot consider observation errors, redundant observation and so on. For this situation, this paper introduces least squares methods of complex data processing and tries to extend surveying adjustments from the real number space to the complex number space. Meanwhile, the two adjustment criteria in complex domain are compared quantitatively. In order to understand effectiveness of complex least squares, the tree height inversion from POLInSAR data is taken as an example. We firstly establish complex adjustment function model and stochastic model for POLInSAR tree height inversion and apply complex least squares method to estimate tree height. The results show that the complex least squares approach is reliable and better than other classic tree height retrieval methods. Besides, the method is simple and easy to realize.

Automatic Mosaic Method of CE2 Lunar Image Based on Local Coordinate System

2014, 43(1):  52-59. 

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To the point of high resolution and mass quantity of images from CE-2, a new projective coordinate system, named local coordinate system, which can be easily built and has a small distortion, was proposed. The DOM and DEM of one orbit could be broken down into some unattached small blocks, every one of which correspond to its own local coordinate system. After the block data was created, a global optimization method, which is based on the overlapped image corresponding points and take the rational polynomial as its model, was applied to correct the coordinate error between overlapped images with the goal of a good registration. There was no interference between image block sub nets because the correction was carried out only in every sub net, which effectively controlled the transfer of error. Experiments indicate the mass lunar images can be processed effectively on the PC by applying the proposed mosaic method and achieve a good result. The panoramic 3D lunar images can be produced at last.

Extracting Roads from High-resolution RS Images Based on Shape Priors and Graph Cuts

2014, 43(1):  60-65. 

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A new road extraction scheme is proposed. First of all, preprocess a RS image with a filter to obtain texture features; then calculate the classic energy function with Graph Cuts to obtain road points, and t-link is constructed with Gaussian Mixture Model; the initial road stripes are achieved with the Line Segment Match Method; lastly, calculate the energy function merged with two shape priors with Graph Cuts to connect roads, which combines the strategy of dynamic segmentation. Experiments of different images testify our algorithm’s effectiveness.

The Application of Bundle Block Adjustment with Conditions in Platform Calibration of Four-Head Aerial Digital Camera

2014, 43(1):  66-73. 

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The method of bundle block adjustment with conditions aims at the four-head aerial digital camera is discussed. The exterior orientation parameters of camera and relative positions of sub-cameras are calculated to derive platform calibration parameters. The experiment results verified that the precision of platform calibration parameters calculated with this method is high, the quality of virtual images are good, and the mapping precision satisfies the large scale and medium scale specifications of survey.

Calibration of Airborne Interferometric SAR Data Based on Reference DEM

2014, 43(1):  74-82. 

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It is significant to study the calibration method without artificial calibrators in terrain mapping and other applications of airborne InSAR in mountainous areas. A new calibration method based on reference DEM without any artificial calibrators is presented in this paper. A reference DEM with known accuracy is used to compare with the DEM generated from InSAR by simulated SAR image. A number of tie points are selected to be ground control points to build the sensitivity matrix via simulated SAR image. Resolving methods are improved based on sensitivity model and the processing of InSAR is combined with calibration to generate DEM. At last, the interferometric parameters are calibrated and the difference between InSAR DEM and reference DEM is calculated to evaluation the precision of calibration. This paper also illustrates the efficiency of this method to airborne InSAR data.

Research of RPC model for DEM generation by InSAR technique

2014, 43(1):  83-88. 

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Synthetic aperture radar Interferometry (InSAR) is a new technique by phase data of SAR complex images for extracting the terrain elevation information, which can solve geographic coordinates of ground points by phase difference of two SAR images. RPC model is a mathematical sense of the imaging geometry model, which is independent of the sensor and platform. This model can establish the relationship between the ground coordinates of the image and the corresponding geographic coordinates. At present, some work has been studied about RPC model as a replacement for Range-doppler model and Phase equation, based on that, this paper states how RPC model is applied for DEM generation by InSAR technique, and then RPC model can be used in four steps, coarse registration, subtract flatten phase, phase height conversion and geocoding. Based on the contrast experiment between COSMO-SkyMed SAR images and ZY-3 optical images for lanzhou area, this paper shows that: mean square error of DEM generated by the RPC model applied for InSAR technology is 7.55 meters

A multi-modal multi-criteria route planning method based on genetic algorithm

2014, 43(1):  89-96. 

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Single criterion routing can not meet the diverse needs of individuals for travel path selection. How to provide multi-criteria routing service has been a hot topic for advanced travel information systems. However, the multi-criteria routing is basically a complex NP problem, and involves different transportation modes. Arbitrary weight assignment for various criterion will remarkably affect the routing results. This paper proposes a multi-criteria route planning method for multi-modal transportation system. It takes the advantage of genetic algorithm for solving optimization problems and extends it to multi-modal routing environment. Various length of chromosome with mode tags is used to encode individuals. Both intra- and inter-mode evaluation operators are defined to guarantee the diversity evaluation. Pareto ranking method with a p-dimensional vector representing multiple criteria is used for fitness calculation. The presented method avoids subjective weight setting procedure, and can obtain various modes combination results for route planning to meet personalized requirements.

Auto-selection Method of Road Networks Based on Evaluation of Node Importance for Complex Traffic Network

2014, 43(1):  97-104. 

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The complex traffic network is constructed based on the generalized topological road network by using dual topology method. By introducing the concept of m-order neighbors and taking into account the factors of the node’s degree, betweenness centrality and distance on the complex traffic network, we consider the importance contributions of the node-self and first to m-order neighbors and define the evaluation model for node importance. Based on this, a road selection process based on the importance contribution of m-order neighbors is proposed, and the selection set is guaranteed to be connected through adopting the minimization principle to network size. In order to verify the efficiency of this process, the degree distribution is introduced to evaluate the level of maintaining the global structure and topological characteristics of road network, and real urban road network is used for experiments of selection. The results show that this road selection process can maintain the global structure of the original road network, maintain the topological characteristics and keep the selected road network well connected, and also this method is stable and reliable.

The multi-granularity description method for route guidance based on hierarchy landmarks

2014, 43(1):  105-112. 

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The route guidance is one of the important researches in the field of navigation and Location Based Service (LBS). The way of traditional guidance information, in an unfamiliar environment, is called Turn-by-turn method, but it is not accord with the people’s cognitive and daily communication habits in the familiar environment. LBD (Landmark Based Description) is much more met requirement, especially for the locals who are familiar with the surrounding environment (such as taxi drivers). It follows the law of people spatial cognitive - from rough to detailed, and can effectively improve the people’s capacity of wayfinding feedback, processing and knowledge sharing. This paper presents a formal model of hierarchy landmarks for different scales of cognitive space in navigation context. It designs a multi-granularity describes method which is more accord with people's cognitive habits for the route guidance.