Research On Key Technologies And Applications Of Digital Lunar System With Unified Spatial Reference

With the rise of a new wave of lunar exploration,lunar exploration and scientific research work has been further deepened.In order to meet the needs of scientific research and engineering demonstration research,it is necessary to establish a digital moon system with unified spatial reference for integration,management,visulization and analysis of the massive,multi-source,multi-scale,and multi-modal lunar exploration data,and to conduct a comprehensive simulation of the three-dimensional scene of the lunar globe,and finally to realize accurate digital description and expression of the Moon.By transcending limits of time and space,the lunar resources can be better recognized,understood,developed and utilized with the support of a digital moon system.Thus,this dissertation studies the key technologes and applications of the digital moon system with unified spatial reference.The main research results are as follows.(1)The digital moon system with unified spatial reference is designed and implemented.According to the characteristics of the Moon,the overall design and demand analysis of the digital moon system are carried out,and the structure and functional modules of the system are designed.The overall architecture of the digital moon system is completed.Three key technologies for constructing the digital moon system are proposed and researched: The first key technology is the organization of the solar system scene with unified space-time reference,which provides space-time information for the digital moon system,so that the digital moon system can be easily extended to other planetary systems in the solar system.The second key technology is the unification of the lunar spatial datum,which realizes the unification of the spatial reference of the lunar global mapping products in the digital moon system by using the spherical registration method;The third key technology is construction of application models for scientific research and engineering demonstration research.Finally,a digital moon system with unified spatial reference integrating massive,multi-source,multiscale and multi-modal lunar exploration data at home and abroad is established.(2)A spherical triangular-mesh-based method for high-precision registration of lunar global mapping products is proposed.Lunar global mapping products provide a solid data foundation for lunar scientific research and exploration.As the widespread geometric inconsistencies among multi-source mapping products seriously affect the synergistic use of the products,high-precision registration of multiple lunar global products is critical,and it is highly challenging due to large coverage and complex local geometric inconsistencies.In this research,we propose a spherical triangular-meshbased method for high-precision registration of lunar global mapping products,which involves four steps: data preprocessing,feature point extraction and matching,spherical Delaunay triangulation,and geometric correction with spherical barycentric coordinates.This global registration method avoids map projection distortions by using spherical coordinates directly,and achieves high precision by confining the geometric models to spherical triangular facets.Experiments are conducted using two groups of different types of mapping products to verify the proposed method quantitatively and qualitatively.The results show that the geometric inconsistencies are reduced from hundreds of pixels to sub-pixel level globally after the registration,demonstrating the effectiveness of the proposed method.(3)A representative application model for scientific research is developed for crater extraction and statistical analysis based on the digital Moon system.A highresolution crater catalogue is established in the Chang’e-5 landing area using the multisource data of the unified spatial reference.Statistics and analysis are carried out,and compared with the deep-to-diameter ratio of the crater catalogue in the Chang ’e-4landing area.The similarity of the deep-to-diameter ratio of the two different areas with a large age difference may indicate that the degradation rate is much larger shortly after craters’ formation than later.In addition,application models for engineering demonstration research,represented by the long-distance accessibility analysis and path planning method of the lunar rover,and the image simulation of the lunar lander and rover,are also developed.In this research,a hierarchical path planning scheme combining high-resolution images and global lunar digital elevation model is proposed to meet the requirements of long-distance accessibility analysis and path planning for future lunar rovers in the new era of lunar exploration.The experimental results of accessibility analysis and path planning from middle Mare Fecunditati to Vallis Snellius show that the proposed method can improve the reliability of the path planning of the lunar rover when the high resolution digital elevation model is limited.The threedimensional simulation scene of lunar surface under real illumination is constructed,and the imaging simulation models of lander and rover cameras are established in the digital moon system.This model can be applied to the engineering demonstration research such as high-precision automatic positioning of the landing point,analysis of the quality and accuracy of the 3D reconstruction from the descent imagery,and accuracy evaluation of the visual positioning of the rover,etc.