Moon-based Extreme Ultraviolet Observations Of The Earth’s Plasmasphere And Image Inversion Methods

The Earth’s plasmasphere, which strongly interacts with the ionosphere, ring current and radiation belt, is the core region for the interaction in the inner magnetosphere. The evolution process of the plasmasphere affects the structures of the inner magnetosphere and the near-Earth space environment. Therefore, research on the plasmasphere has important scientific and application values. As a payload of the Chang’E-3 mission in the Second Phase of Chinese Lunar Exploration Program, the moon-based extreme ultraviolet （EUV） imager will image the 30.4 nm emission resonantly scattered by the plasmaspheric helium ions from the sunlight to monitor the responses of the plasmasphere to geomagnetic activities, and to provide important data to research the latitudinal distribution properties of the plasmasphere and the coupling in inner magnetosphere. This dissertation is mainly targeted on the 30.4 nm radiation properties of the plasmasphere and the inversion method for the moon-based plasmaspheric EUV images, and thus to provide basis for the design of moon-based EUV imager and analysis of moon-based EUV images.The methods of theoretical model simulation combined with satellite data analysis are adopted in this dissertation to investigate the dynamic properties and EUV radiation properties of the Earth’s plasmasphere. The results show that:1. The Earth’s plasmasphere is mainly located within 6.0 RE on the magnetic equatorial plane and within 4.0 RE on the meridian planes, and the typical scale size of the plasmapause, shoulder and plume is 0.1 RE. The average radial velocity of erosion or refilling of the plasmasphere during geomagnetically disturbed periods is 0.7 RE/h, corresponding to 0.1 RE in 10 min.2. The 30.4 nm radiation intensity of the plasmasphere detected from the moon is 0.1¹0.7 Rayleigh within the plasmapause and 0.02⁰.10 Rayleigh outside the plasmapause. The radiation intensity in plasmasphere trough region may increase to 0.1 Rayleigh during storm times.3. The EUV images of the plasmaspheric shoulder and plume are simulated from the moon for the first time. Temporal evolutions of the plasmaspheric EUV radiation intensity are also modeled from the moon for the first time.The orbital characteristics and surface environment properties are investigated in this dissertation. During one lunar revolution period, the total imaging period for the moon-based EUV imager is 11.5 earth days, during when the maximum latitudinal drift of the positioning of the imager is 10.8°while the maximum longitudinal drift is 6.5°. The EUV radiation reflected by lunar surface is approximately 2.0 Rayleigh at solar maximum, which has the same order in terms of magnitude compared with the plasmaspheric radiation. Researches on the topographic properties of the five planned lading sites reveal that the EUV radiation reflected by lunar surface of these sites can not enter the field of view of the imager. For the five sites, Sinus Iridum is the most idea site for moon-based EUV imaging. The total fluences of electrons and protons during one year at solar maximum are both approximately 5.0×10¹⁵ cm^-2. In addition, during one lunar revolution period, the surface temperature changes from 80.0 K at lunar night to 390.0 K at lunar noon.According to the above results, the design requirements for the moon-based EUV imager are verified: central wavelength of 30.4 nm, field of view of 15.0°, angular resolution of 0.1°, temporal resolution of 10 min or better, detecting intensity scope of 0.1-10.0 Rayleigh, azimuthal adjusting scope of±6.5°, latitudinal adjusting scope of 58.0°, and the imager must meet the requirements for particle exposure dose and temperature changes. Based on the simulated moon-based plasmaspheric EUV images, the magnetic equatorial plane plasmapause is reconstructed with Minimum L Algorithm first, then the quasi three-dimensional He+ density distribution is inversed with Genetic Algorithm. The averaged relative density error is 8.0%, which satisfies the requirements of scientific research and space weather forecast. This algorithm solves the proglem of reconstructing the plasmasphere from moon-based plasmaspheric EUV images for the first time, and provides method for researches on latitudinal distribution properties of the plasmasphere and coupling of plasmasphere to inner magnetosphere.