Euv Images Of The Earth's Plasmasphere And The Use Of Ct Reconstruction Of Its Global Density Distribution

Plasmasphere is one important part of the inner magnetosphere. Apart from electron and H+, which have no optical emission, He+ is the most abundant ion in the plasmasphere. Because the density of He+ is correlated with the H+, so the density structure and behaviour of He+ can represent the dynamics of the whole plasmasphere. The Extreme Ultraviolet Imager (EUV) instrument aboard the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission performs global imaging of the plasmasphere through the He+ outside Earth's shadow resonantly scattered the solar 30.4 nm radiation. In this dissertation, we analyze the data from EUV, and focus on the structures and rotation of the plasmasphere. Furthermore, the feasibility of deduction of the global density of the plasmasphere from the observation images using Computed Tomography technique is discussed.The rotation of the plasmasphere is studied by using a large and having a comparatively great duration plasmaspheric notch. The analysis reveals that, the rotation rate varied with the magnetic local time, and also with the distance L from the Earth's center in the equatorial plane. On the same L, the rotation rate remains higher in the dawn region than in the dusk, and the difference of the rotation speeds on same annulus is more obvious when L is large. With the increase of L, the rotation rate tends to slightly increase on the dawn-side, and the plasma finally moves eastward relative to Earth. On the contrary, it tends to strongly decrease on the dusk-side. That is, there is a larger decrease on the dusk-side and a smaller increase on the dawn-side. When retrieving the plasmasphere density from the EUV images, we introduce a new method, which is Computerized Tomography (CT) technology. However, theEUV data is very different from the data sampled by traditional CT, which brought two significant problems in our study. The problems are incomplete projection data and variable plasmasphere. In order to verify the feasibility of CT, we built simple plasmasphere phantom, and then the numerical simulation method is used to reconstruct the phantom. There are three representative methods of CT, which are the Algorithm of the Back Projection (ABP), Filtered Back Projection (FBP) and the Algebraic Reconstruction Technique (ART). Through comparing the three reconstruction of the plasmasphere phantom, it is shown that the high quality image is achieved by using the ART method. Furthermore, we develop an improved ART method based on the minimization of the image total variation (TV), and reconstruct the 3-D density distribution, which has yielded highly desirable results. In the end, by reconstructing the phantom through simulating the real IMAGE position in an orbit, the result has established that we can retrieve the global density of the plasmasphere from the EUV images.