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Bu Y.,Beijing Aerospace Control Center | Tang G.,Beijing Aerospace Control Center | Liu H.,National University of Defense Technology | Pan L.,National University of Defense Technology
Chinese Journal of Aeronautics | Year: 2013

In the paper, a set of algorithms to construct synthetic aperture radar (SAR) matching suitable features are firstly proposed based on the evolutionary synthesis strategy. During the process, on the one hand, the indexes of primary matching suitable features (PMSFs) are designed based on the characteristics of image texture, SAR imaging and SAR matching algorithm, which is a process involving expertise; on the other hand, by designing a synthesized operation expression tree based on PMSFs, a much more flexible expression form of synthesized features is built, which greatly expands the construction space. Then, the genetic algorithm-based optimized searching process is employed to search the synthesized matching suitable feature (SMSF) with the highest efficiency, largely improving the optimized searching efficiency. In addition, the experimental results of the airborne synthetic aperture radar ortho-images of C-band and P-band show that the SMSFs gained via the algorithms can reflect the matching suitability of SAR images accurately and the matching probabilities of selected matching suitable areas of ortho-images could reach 99 ± 0.5%. © 2013 Production and hosting by Elsevier Ltd. on behalf of CSAA and BUAA. Source

Di K.,CAS Institute of Remote Sensing | Xu B.,CAS Institute of Remote Sensing | Peng M.,CAS Institute of Remote Sensing | Yue Z.,CAS Institute of Remote Sensing | And 4 more authors.
Planetary and Space Science | Year: 2016

This paper presents a comprehensive analysis of the rock size-frequency distribution at the Chang'E-3 landing site. Using 84 Navcam stereo images acquired at 7 waypoints by the Yutu rover and an interactive stereo image processing system, a total of 582 rocks larger than 0.05 m in diameter were identified and measured. The statistical results of the size-frequency distribution show that the cumulative fractional area covered by rocks versus their diameter follows a simple exponential function and has a convex-up shape on log-log graphs with the slope increasing with diameter. The cumulative number of rocks versus diameter derived by numerically integrating the cumulative fractional area also shows a good fit with the data. A diameter-height relationship was also determined from height and diameter ratios. The observed rock statistics were also compared with those from other lunar missions, including the Surveyor, Apollo, and Lunokhod missions; results suggest that the rock distribution at the Chang'E-3 landing site is similar to that found by Surveyor III. © 2015 Elsevier Ltd. All rights reserved. Source

Xia J.,Beijing Aerospace Control Center | Tang G.,Beijing Aerospace Control Center | Han C.,Beihang University | Cao J.,Beijing Aerospace Control Center | And 2 more authors.
Lecture Notes in Electrical Engineering | Year: 2015

Nowadays there are more than 30 GNSS satellites equipped with laser retro-reflectors. Orbits of these satellites can be independently validated with a high precision using range observations by satellite laser ranging (SLR). China has completed the Asia-Pacific area COMPASS Satellite Network, and is committed to the establishment of the international GNSS Monitoring and Assessment System (IGMAS). Orbit validation is one of the key factors in the development of IGMAS, so this paper validated almost all GNSS satellites carrying reflectors to see whether the IGMAS orbits is qualified, including all 24 of GLONASS, 4 of COMPASS, 4 of GALILEO based on the rapid orbits from BACC IGMAS Analysis center. According to IERS2010 convention, correction models such as station coordinates, laser propagation delay models were introduced to establish the measurement model. The validation of the BACC orbits shows a mean deviation around 5–10 cm for the GLONASS satellites, 10–15 cm for the COMPASS MEO/IGSO satellites, 2.65 m for the COMPASS GEO satellites, and 20–25 cm for the GALILEO satellites. © Springer-Verlag Berlin Heidelberg 2015. Source

Bu Y.,Beijing Aerospace Control Center | Tang G.,Beijing Aerospace Control Center | Ding C.,CAS Institute of Electronics | Liu J.,Beijing Aerospace Control Center | And 2 more authors.
2014 IEEE Chinese Guidance, Navigation and Control Conference, CGNCC 2014 | Year: 2015

On December 13, 2012, China's Chang'e 2 Spacecraft successfully flew past No.4179 Asteroid Toutatis, and acquired a series of clear optical images concerning Toutatis. The data obtained is very important for us to be able to establish feasible methods for deep-space optical navigation. However, as the fly-by process cannot be repeated and deep-space environments cannot be tested using physical platforms on the ground, the problem concerning how to verify the correctness and accuracy of optical positioning algorithms emerges. According to the fly-by strategy of Chang'e 2 to detect Toutatis, in combination with navigation motion relationships between the spacecraft and the asteroid, such as orbit and position, and in light of actual data and problem models, the paper constructs a set of algorithms of ground numerical appraisal for relative positioning accuracy when Chang'e 2 flies past Toutatis. Through three relative positioning algorithms, conducting algorithm testing of ground numerical appraisal, which effectively appraises the positioning algorithm accuracy through numerical methods and clearly explains the sources of random error and system error, This method can be used as the basic means for ground verification of deep-space optical navigation algorithms. © 2014 IEEE. Source

Peng M.,CAS Institute of Remote Sensing | Wan W.,CAS Institute of Remote Sensing | Wu K.,CAS Institute of Remote Sensing | Liu Z.,CAS Institute of Remote Sensing | And 5 more authors.
Journal of Remote Sensing | Year: 2014

China's Chang'e-3(CE-3) probe, which includes a lander and a rover, successfully landed on the lunar surface on December 14, 2013.High precision and automatic mapping of the lunar surface surrounding the rover is of fundamental importance both for safe rover navigation and for achievement of scientific and engineering goals. During CE-3 mission, we routinely produced topographic maps, and rover traverse maps to support surface operations of the rover. In this research, we focused on mapping capability analysis and fast terrain reconstruction using Navcam (navigation camera)stereo images acquired by Yutu rover. First, we performed topographic mapping capability analysis of Navcam stereo pairs using basic photogrammetric principles and error propagation law, and empirical formula. The expected measurement error of Navcam stereo images is less than 2 m within 44 m from the rover, and less than 1 m within a range of 31 m. To give a theoretical estimation of the mapping errors at different locations, a covariance matrix is used to depict the position error. The position errors are mainly in the radial directions. Given that the elevation differs in different distances, grid error in DEM is analyzed based on linear interpolation model, the elevation accuracy is higher than the horizontal accuracy. In order to complete terrain mapping, we presented a multi-threaded image processing method for fast generation of topographic products using rover images. The whole mapping process include automatic feature points extraction based on epipolar images, multi-threaded dense matching, three-dimensional compution, DEM interpolation by a parallel processing combined with multi-thread technique. First, epipolar images were generated using exterior orientation parameters, then bundle adjustment was used to refine the exterior orientation parameters of the rover images. Moreover, a triangulated irregular network-controlled dense image matching method was adopted for dense grid matching. After image dense matching, three-dimensional positions of the matched points were calculated using space intersection with co-linearity equations. The final DEM was generated using Kriging interpolation. To verify the accuracy of our method, experiments were conducted using simulated data. Seven pairs of stereo images were simulated using resampled 0.01 m CE-2 DEM and DOM. A new DEM with 0.02 m resolution is generated from the simulated images; and 12 check points are used to verify the accuracy. The RMSEs(Root Mean Square Errors) of these GCPs are 0.036 m, 0.051 m and 0.014 m in three directions. Experimental results using stereo images at waypoint D acquired by Yutu rover also demonstrated the effectiveness and accuracy of the method. Until January 17, 2014, Yutu rover has traveled 114.8 m on lunar surface and performed a series of scientific investigations. The developed terrain mapping techniques and software have been routinely used in Chang'e-3 mission operations. Topographic products (DEM and DOM) were generated quickly and at 17 waypoints using Navcam images based on multi-threaded image processing to support mission operations. Source

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