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 Title: Quantification of the spatial structure and temporal variability of Earth's exosphere using optical tomography Author(s): Cucho Padin, Gonzalo Augusto Director of Research: Waldrop, Lara Doctoral Committee Chair(s): Waldrop, Lara Doctoral Committee Member(s): Ilie, Raluca; Kamalabadi, Farzad; Liang, Zhi-Pei Department / Program: Electrical & Computer Eng Discipline: Electrical & Computer Engr Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Tomography exosphere optical remote sensing UV emission atomic hydrogen Abstract: Knowledge of the spatial structure of Earth's exosphere, the outermost atmospheric layer, is crucial for understanding various aspects of aeronomy and heliophysics, such as atmospheric chemistry and energetics, magnetospheric energy dissipation, ion-neutral coupling, and atmospheric evolution. Atomic hydrogen (H) is the dominant constituent in this region, where it forms a mostly gravitationally bound cloud that extends from several hundred to several tens of thousands of kilometers above Earth's surface. For the past decade, the Lyman-Alpha Detectors (LADs) onboard the National Aeronautics and Space Administration (NASA) Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) mission have obtained routine measurements of solar Lyman-Alpha (Ly-a) photons at 121.56 nm that are resonantly scattered by exospheric H atoms. This thesis presents a new means of global, three-dimensional quantification of exospheric H density through tomographic inversion of scattered H Ly-a emission. This approach avoids the historical dependence on ad hoc parametric formulations of the H density distribution and enables more reliable characterization of global outer exospheric. The incorporation of the temporal domain into the tomographic approach through Kalman filtering allows, for the first time, analysis of the temporal evolution of global exospheric structure during periods of major disturbances in Earth's magnetic and plasma environment known as geomagnetic storms. This thesis presents several case studies of both static and time-dependent H density estimation during quiet- and storm-time conditions. This work yielded two primary findings: (i) solar radiation pressure induces Sun-Earth alignment of global exospheric structure only evident on long timescale observations (i.e., seasonal averaged) but not present in a single-day 6-hours observation interval, and (ii) geomagnetic storms induce density enhancements that propagate slowly outward. This thesis also presents an analysis of terrestrial ring current evolution driven by its charge-exchange interaction with exospheric H atoms. Historical investigations of the ring current typically adopt spherically symmetric, static H density specifications, while this thesis presents the first results using time-variant H density distributions derived tomographically from TWINS radiance data acquired during a strong geomagnetic storm. Simulation of the ring current using the Comprehensive Inner Magnetosphere Ionosphere model and the incorporation of the time-dependent H density specification yields realistic temporal evolution of ring current energetics and motivates future consideration of exospheric dynamics during geomagnetic storm recovery. Despite the significant advances in exospheric physics that tomographic analysis of TWINS/LAD data has enabled, the benefits are limited ultimately because the data is intermittent and regionally confined. This thesis describes a new exospheric mission concept that features constellation deployment of Ly-$\alpha$ imagers for optimal multiscopic sensing in support of the tomographic reconstruction of fully global H density at a high temporal cadence. This mission concept exploits the upcoming NASA Artemis mission, formerly known as the Deep Space Gateway, which will be deployed near Lunar orbit. This thesis provides a detailed description of the viewing geometry, concept of operations, statistical data analysis approach using tomography, and technique validation based on synthetic data. The mission concept yields global quantification of exospheric structure with unprecedented spatial and temporal resolution, thereby enabling significant advances in the coupling of Earth's magnetosphere-exosphere system and its response to solar inputs. Issue Date: 2021-07-15 Type: Thesis URI: http://hdl.handle.net/2142/113052 Rights Information: Copyright 2021 Gonzalo Augusto Cucho Padin Date Available in IDEALS: 2022-01-12 Date Deposited: 2021-08