The star tracker should be accurately calibrated in order to achieve high precision. The calibration procedure can be well performed in the laboratory with the aids of a high-precision two-axis rotary table. Hence, the calibration accuracy is heavily relied on the performance of the rotary table. In this paper, use a collimator to emit starlight, then the influence of the rotary table error on the calibration result of the star tracker is analyzed in detail. The simulation and experimental results show that the accuracy of the rotary table has a great influence on the laboratory calibration results. When the rotary table error is 2 '' Gaussian error, the attitude angle calibration error is within 3 '' . The intrinsic parameters calibration accuracy are as follows, the principal point error is within 5 pixels, the focal length error is 0.001mm, less than 20% deviation of tangential distortion, radial distortion within 120% deviation. Except the declination error and the fixed angle along the optical axis error is within 5 '' , the remaining extrinsic parameters have relatively large errors, but they have limited influence on the calibration results, for the star tracker calibration only focuses on the accuracy of the intrinsic parameters. The reprojection error of the star centroid is in a few hundredths of a pixel, and the corresponding angle error is 3 ''~5 '' , which can satisfy the high-precision attitude measurement of the star tracker.
MOOC(Massive Open Online Course) is a new teaching model that has been springing up since 2012. The typical characters are short teaching video, massive learners, flexible place and time to study, etc. Although MOOC is very popular now, opto-electronic MOOCs are not much enough to meet the need of online learners. In this paper, the phylogeny, the current situation and the characters of MOOC were described, the most famous MOOCs’ websites, such as Udacity, Coursera, edX, Chinese College MOOC, xuetangx, were introduced, the opto-electronic MOOCs come from these famous MOOCs’ website were investigated extensively and studied deeply, the “Application of Opto-electronic Technology MOOC” which was established by our group is introduced, and some conclusions are obtained. These conclusions can give some suggestions to the online learners who are interested in opto-electronic and the teachers who are teaching the opto-electronic curriculums. The preparation of “Opto-electronic Technology MOOC” is described in short.
The determination of optical system parameters is the first step in the design of optical system of star sensor. In this paper, the influence of the field of view, focal length and relative aperture of the optical system on the star sensor is analyzed. In the selected detector conditions, according to the field, the focal length, and the magnitude of threshold of mutual restriction, signal-to-noise ratio, the size of the catalog and optical system design considering the level of to determine the optical system of the field, focal length, relative aperture, magnitude of threshold, spectral range and center wavelength. In order to meet the signal to noise ratio, the stellar detection limit, detection probability and other requirements, the selected detector were calculated. The method of determining the parameters provide a reference for the design of the optical system of star sensor.
Combining with the fold line videometrics, a method for pose estimation based on monocular measurements is studied. The method to measure the inertial position of the Photometric transfer station and the Orthogonal Iterative Algorithm based on the image space collinearity error is summarized. Then, the mistake using the Singular Value Decomposition (SVD) to solve is described and then introduce the improving algorithm. Finally, the Simulation and actual experiment is done to verify the accuracy of pose estimation using the fold line videometrics. The results show that the precision can reach 1mm or less using a camera with the resolution of 1280 by 1024 pixels, in the condition of 4.5 meter capturing distance and a Leica TS30.
KEYWORDS: Cameras, Temperature metrology, 3D modeling, Imaging systems, Systems modeling, Image analysis, 3D image processing, Thermal effects, Coded apertures, Calibration
Temperature variations will affect the geometric and optical characteristics of the camera and lens in the videometric system, especially when the optical systems are working in a long period. The paper presents an analysis of the image drift caused by temperature variations and the corresponding temperature compensation method. Firstly, image drift model is established based on the pinhole camera model; then two simplified models are introduced by analyzing the coupling relations between the variations of camera parameters and temperature; furthermore, influence of temperature changes on camera parameters were modeled and calibrated; pose estimation experiments as well as temperature compensations are also conducted in deformation measurements, and the results prove the feasibility and efficiency of the proposed models.
Synthetic aperture radar interferometry (InSAR) is a rapidly developing technique for earth observation. Differential InSAR (D-InSAR) technique, based on InSAR, is a method for earthquake deformation detection and land subsidence monitoring. A method of generation of interferogram for D-InSAR using adaptive contoured correlation interferometry is presented, which may directly generate an interferogram with almost no speckle noise or blurring. The data processing results of the Mani earthquake indicate that the proposed method can effectively reduce decorrelation noise, even in areas with serious decorrelation.
When the videometric method is working during a long period, the temperature effects on cameras and lens will cause changes in optical axis, focal length and aberration coefficients, so as to influence the accuracy and reliability of measurement results. The features of typical structure of camera lens when it is applied by thermal stress are analyzed in this paper. The model of key parts of camera lens which influence the measure accuracy mostly is built firstly, then the thermal stress is calculated and the influence of thermal transmutation to the measure accuracy is analyzed. Finally, suggestion to improve the structure of camera lens is proposed.
Repeated plastic instability accompanying serrated yielding in stress–strain curves and localization of deformation is observed during plastic deformation of many metallic alloys when tensile specimens are deformed under certain experimental conditions of temperature, strain rate, and pre-deformation. This phenomenon is referred to as the Portevin- Le Chatelier (PLC) effect. TMW alloy, a newly developed Ni–Co base superalloy for aircraft engine application, also exhibit PLC effect during tensile test at temperatures ranging from 300 ℃ to 600 ℃, which are also the temperature range for engine working. In this paper, a 3D digital image correlation (3D DIC) measurement system was established to observe the localization of deformation (PLC band) in a tensile test performed on TMW alloy specimen at temperature of 400 ℃. The 3D DIC system, with displacement measurement accuracy up to 0.01 pixels and strain measurement accuracy up to 100 με, has a high performance in displacement field calculation with more than 10000 points every second on a 3.1G Hz CPU computer. The test result shows that, the PLC bands are inclined at an angle of about 60° to the tensile axis. Unlike tensile test performed on aluminums alloy, the widths of PLC bands of TMW alloy specimen, ranging from 4 mm to 4.5 mm, are much greater than the specimen thickness (0.25 mm).
A new synthetic aperture radar interferometry (InSAR) data processing method comprehensively based on three parts of complex images is introduced. The method includes image pair registration and interferogram creation. These methods are improved and extended, and a set of integrated technology, which is named contoured correlation interferometry (CCI), is formed for the InSAR data processing. The CCI method needs only an arbitrary three parts of InSAR complex image pair to generate an interferogram without noise and blurring effect. The formulae of the CCI method are deduced and proved in a different way, the details and steps of the whole method are explained systemically, the algorithms for the calculation of fringe orientations are improved, and the discussions about selecting of parameters and comparing results of different methods are shown.
Coherence of interferometric synthetic aperture radar (InSAR) complex image pair is a fundamental observable in interferometric radar measurements, which is usually measured by comparing the radar return across several nearby radar image pixels and has found diverse applications. This paper proposes a coherence estimation method which requires three arbitrary parts of the two complex images to implement interference. The proposed method can also be used to co-register InSAR image pair, which means that the imaginary part of the master image can be left away. In addition, an improved quality-guided phase unwrapping method is forwarded with the quality map generated by the coherence estimation method we have recommended above. A look-up table is adopted to reduce the processing time. The experimental results show that both methods are effective and greatly reduce the phase unwrapping time compared with the existing quality-guided methods.
Speckle fringe patterns of ESPI are full of high-spatial-frequency and high contrast speckle noise which defies normal
process methods. Filtering with contoured windows has been proven to be an efficient approach to filter off the speckle
noise while reserving the fringe patterns obtained by subtraction of two original speckle patterns. Furthermore, with
contoured windows, the contoured correlation fringe pattern (CCFP) method proposed by the authors can derive highquality
fringe patterns of ESPI with speckle-free, smooth, normalized and consistent fringes from two original speckle
patterns. CCFP method can also extract the phase field with a single-step phase-shifting. Determination of contoured
windows is a key step in CCFP method. The contoured windows used to be determined by fringe orientations only and
this process would generate accumulated errors. In this paper, two new algorithms to determine the contoured windows
according to the fringe intensity slope and the distance ratio to neighboring skeletons with the help of the local fringe
direction are proposed. These new techniques can determine contoured windows more precisely and more robustly with
no accumulated errors. Some applications of our new contoured windows are also presented.
Removing speckle noise in electronic speckle pattern interferometry (ESPI) from a single speckle fringe pattern while keeping the fringe features is a difficult problem. The spin filtering with curved surface windows proposed by the authors is successful to filter out speckle noise nearly completely from a single speckle fringe pattern. However the new filtering has a difficulty to be overcome that the speckle fringe orientation map (SFOM) depends on the processing window size which is tryout and is difficult to be derived correctly when the speckle fringe density changes considerably. In this paper we utilize the original speckle pattern sequence with one-beam setup to determine the speckle movement direction field by digital correlation methods so that the SFOM is determined from the direction field. In this way the SFOM can be derived regardless of fringe density.
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