【作者】 孙伟英；

【导师】 吴季；

【作者基本信息】 中国科学院研究生院（空间科学与应用研究中心） ， 空间物理， 2006， 博士

【摘要】 太阳风是对人类活动产生直接影响的日地系统之链,充满着整个日地行星际空间。受到太阳活动导致的太阳风变化的影响,地球空间环境会产生变化,这些变化会引起一系列影响人类活动的事件。CMEs是尺度最大、最壮观的太阳活动。对CMEs造成的地球空间环境变化尽可能早的预报,对避免或减少灾害性空间天气对地球空间及人类活动的影响具有重要的科学与应用意义。把CMEs引起的行星际扰动和产生的地磁活动作为一个相互联系的有机链,是当前国际空间天气研究的主要发展趋势之一。中科院空间中心提出的太阳极轨射电望远镜(SPORT)计划设想在太阳极轨卫星上,利用微波甚至射电频段对CMEs传播导致的行星际高密度等离子体云进行成像遥感观测,从而获得对地球空间天气的预报、预警。这在人类尚属首次,具有非常重要的科学意义以及重要的应用前景,将对日地空间天气系统的研究和应用产生重要作用,并为国际与日共存计划做出重要贡献。本论文的研究内容是SPORT计划中的核心与关键技术部分,主要包括:通过对卫星测量数据的分析研究,建立行星际空间等离子体电子密度随日心距变化的理论模型;研究太阳宁静期间日地行星际等离子体云及CMEs在行星际传播时导致的高密度等离子云的射电辐射机理;计算相应的射电辐射亮温;对比分析LASCO日冕仪及Nancay射电日光仪观测到的CME图像。研究辐射测量、孔径综合、二元干涉测量原理;分析天线阵稀疏孔径设计对提高综合孔径辐射计空间分辨率的意义;研究解决稀疏孔径设计问题的算法;利用SA算法,设计稀疏孔径设计的具体流程;数值模拟旋转扫描阵列的稀疏孔径设计,包括:圆环、圆平面阵列零冗余及阵列框架重心逼近圆心、低冗余度设计。研究辐射计成像系统的构成、主要参数,分析辐射计图像的特征;分析日地行星际高密度等离子体云及天体的辐射计成像的可行性;设计模拟日地行星际高密度等离子体云和天体辐射计图像的具体方法;对预计的SPORT计划中行星际天体和ICMEs导致的高密度等离子云的辐射计图像进行模拟和分离。更多还原

【Abstract】 Solar-terrestrial interplanetary space is filled with solar wind, which is the chain ofsolar-terrestrial system. The variation of geospace environment, which is provoked byfluctuation of solar wind that caused by solar activities, will induce a serious of eventsthat influence human activities. CMEs are the solar active phenomenon with maximumdimensions. It is of great scientific interest that the influence of disastrous space weatheron geospace and human activities is avoided or reduced via forecast of geospaceenvironment variation which is induced by CMEs.At present, it is a main trend on space weather study that interplanetary turbulenceand geomagnetic activity caused by CMEs are considered as an interconnection globalsystem. SPORT (Solar Polar Orbit Radio Telescope) project is a solar wind monitoringmission proposed by Center for Space Science and Applied Research, Chinese Academyof Sciences. It conceive that the high density plasma clouds in interplanetary spacewhich induced by the propagation of CMEs are imaged firstly by radiometer withmicrowave or meter waves. Consequently, the forecast or earlywarning of geospaceweather will be obtained. This project is of great scientific interest and importantapplied prospect. It will have significant effect on study and application ofsolar-terrestrial space weather system and contribute to ILWS project. Research contentsin this paper, which are part of the core and key techniques of SPORT, mainly conclude: The theoretical model of electrons density variation of interplanetary spaceplasma with heliocentric distance is established via analyses and study onsatellite measured data. The radiation mechanisms of space plasma in times ofquiet sun and of high density plasmas clouds in times of CMEs propagating ininterplanetary space are researched. The radio emission brightnesstemperatures of them are also calculated. CME image that obtained byLASCO and NRH are analyzed contrastively. Radio emission measurement, aperture synthesis and two-elementinterferometry theory are studied. The significance of thinned antenna arraydesign on improving spatial resolution of synthesis aperture radiometer isanalyzed. Algorithms that can be used to resolve the problem of thinnedantenna array design are investigated. Specific flow of the thinned antennaarray design with SAA is devised. The design of thinned antenna array withrotating scanning mode are simulated, which including the design of zeroredundancy, low redundancy besides the framing gravity center approachcenter of circle of ring arrays and circle plane arrays.The composition and main parameters of image-forming system of radiometerare studied. The characteristics of radiometer images are analyzed. Thefeasibility of obtaining radiometer image of high density plasma clouds andcelestial bodies in solar-terrestrial interplanetary space is analyzed. Simulationand separation of the image are realized by use of the detailed method ofsimulating that given in the paper.1. Study on radio emission of solar-terrestrial interplanetary plasma cloudsElectrons density, temperature and other parameter values of plasma in 0.00465-1AUinterplanetary space are statistically listed by using the data in reference [62, 65] andmeasurement data from Mariner l0. Furthermore, CMEs events that accompanied by solar radiobursts and plasma values near L1 point that affected by these events are also statistically listed.On the basis of study of the varied tendency of number density of solar wind corpuscularstream with the variation of heliocentric distance, the corresponding electrons density ofplasma in interplanetary space is estimated as per ne ’ = 2n/ 2×4.73×ne . Moreover,other parameter values of the plasma are also calculated.The variation of interplanetary space plasma parameters in times of CMEspropagating are analyzed on the basis of study of the various radiation mechanisms ofspace plasma. The results show that the high density plasma clouds that induced byICMEs still belong to the category of non-relativistic plasma in despite of differentinfluence in interplanetary space that induced by various ICMEs. Their mainmechanisms of radio radiation are bremsstrahlung, a small amount of cyclotronradiation and a still weaker recombination radiation. The bremsstrahlung brightnesstemperatures of space plasma in times of quiet Sun and of high density plasma clouds intimes of CMEs propagating in 0.00465-1AU interplanetary space are calculated. Thecalculated results show that the detective frequency of radiometer with 1-3K resolutionshould be selected at 30±5MHz when taking image of the high density plasma clouds.Also, solar microwave bursts which are associated with CMEs in the same periodare investigated. The results show that the main radiation mechanisms are thermalbremsstrahlung, cyclotron resonance radiation, plasma radiation and electroniccyclotron maser radiation. The images of CME, which occurred in 1998.4.20, thatobtained respectively by LASCO and NRH are analyzed contrastively. The study showthat the radiation mechanisms of it that observed by LASCO are recombinationemission and bremsstrahlung, and the radiation mechanism of it that observed by NRHis bremsstrahlung.2. Study on thinned antenna array designIn this paper, SAA is selected to realize the thinned antenna array design via studyof various algorithms which can be used to resolve the thinned antenna array designproblem. On the basis of study of principle, cooling schedule and basic characteristicsof SAA, t 0= 900, α = 0.9999and L k= 100n are selected after a large number ofnumerical simulations. Furthermore, functions of state generation, state acceptance,temperature refreshment and termination criterion of extrinsic cycle are established. Thespecific flow of thinned antenna array design is also provided.Solutions are obtained for ring arrays and planar arrays with in a circle with 7-10elements in the paper. The results show that zero redundancy and low redundancybesides the framing gravity center approach center of circle of the ring arrays and planararrays with in a circle are obtained. Various design schemes have different feature andsuperiority. Therefore, the appropriate scheme should be selected according to thescientific objects and requirements as practically applying.3. Study on the simulation and separation of radiometer images of high densityplasma clouds and celestial bodies in interplanetary spaceSo far no precedents have been discovered that radiometer is used to detectinterplanetary solar wind. In this paper, the feasibility of obtaining radiometer images ofhigh density plasma clouds and celestial bodies in solar-terrestrial interplanetary spaceis studied. Furthermore, the significance of simulating and separating the images isanalyzed. The detailed method of simulating and separating the images is alsoinvestigated.The related parameters as simulating are set as follows. The imaging domain ofspace-borne radiometer is 2×2AU. The pixel resolution is 0.008AU. The grey scale ofimage is 64. The grey scale of summation of cosmic background radiation, thermalnoise of antennas and receivers is 12. The results of numerical simulation show that it isa feasible plan to simulate and separate the radiometer images of high density plasmaclouds and celestial bodies.In general, the selected topic of this paper has not only significance of theoreticalstudy but also application prospect of vital space exploring projects. The researchfindings of this paper provide important theoretic basis and powerful technical supportfor the application of radiometer to space detection. Therefore, a new clew that is worthusing for reference is also provided for detecting interplanetary solar wind.更多还原