Previous plasma imaging missions have used time-delay integration techniques that correct for uniform motion blur during integration. This was due to the assumed constant range-to-target of each pixel in the observed scene. ICON's low orbital altitude and twelve second integration time create non-uniform motion blur across the observed scene and necessitate a novel variable-range time-delay integration (TDI) algorithm be used to spatially resolve the two-dimensional images. The variable-range TDI algorithm corrects for each pixel moving at a different angular rate throughout image integration and transforms each raw image onto a surface where the spacecraft is moving at a constant angular rate with respect to every pixel in the image. Then as the raw images are co-added together the non-uniform motion of the observed scene is accounted for and will not geographically distort the final images, or any features seen within them. Through simulation using output from the SAMI3 model during plasma depletion formation it was determined that the structuring and gradients of plasma depletions can be recovered using this technique. Additionally, the effects of depletion width, solar activity level, and misalignment of the field-of-view with the local magnetic field were investigated. The variable-range TDI technique is able to recover the overall shape and depth of depletion of the depletions in all cases, however the determination of gradients observed at depletion walls is significantly degraded for very narrow plasma depletions and during periods of low solar activity. All simulated model conditions were shown to be representative of current ionospheric conditions. / Master of Science / Equatorial spread-F, also termed plasma bubbles, is a phenomenon that occurs in the equatorial region of Earth’s ionosphere, the charged region of Earth’s atmosphere. Plumes of less dense plasma, the charged material of the Ionosphere, rise through regions of higher density plasma. This causes disturbances to radio signals that travel through this region, which can lead to GPS range errors or loss of signal. ICON is a NASA Explorer mission aimed at, in part, understanding the sources of variability in the ionosphere. One instrument onboard ICON to accomplish this goal is the FarUltraviolet Imager which images airglow in the far-ultraviolet range. During nighttime, the FUV imager can observe plasma bubbles to study the instability and the mechanisms that produce it. This thesis looks at the ability of the variable-range time-delay integration (TDI) algorithm, used to produce images from ICON’s Farultraviolet imager, to spatially resolve the structure and gradients of observed plasma bubbles. However, due to the viewing geometry of ICON’s FUV imager, each pixel across the observed scene experiences a different angular rate of motion blur. The variable-range TDI algorithm removes this non-uniform motion blur by transforming each raw image onto a surface where the spacecraft moves at a constant angular rate with respect to every pixel in the image. Then raw images are integrated together such that the observed scene is not geographically distorted. It was concluded that the TDI process is able to spatially resolve a wide variety of plasma bubbles under various ionospheric conditions and imager configurations.

Thesis advisor: Prof. Michael J. Naughton / Thesis advisor: Dr. Cesar E. Valladares / The equatorial and low-latitude ionosphere of the Earth exhibits unique features on its structuring, coupling, and electrodynamics that offer the possibility to forecast the dynamics and fluctuations of ionospheric plasma densities at later times. The scientific understanding and forecasting of ionospheric plasma are necessary for several practical applications, such as for mitigating the adverse effects of space weather on communication, navigation, power grids, space mission, and for various scientific experiments and applications. The daytime equatorial electrojet (EEJ), equatorial ionization anomaly (EIA), as well as nighttime equatorial plasma bubble (EPB) and plasma blobs are the most prominent low-latitude ionospheric phenomena. This dissertation focuses on the multi-diagnostic study of the mechanism, properties, abnormalities, and interrelationships of these phenomena to provide significant contributions to space weather communities from the ground- and space-based measurements. A strong longitudinal, seasonal, day-to-day variability and dependency between EEJ, ExB vertical plasma drift, and total electron content (TEC) in the EIA distribution are seen in the equatorial and low-latitude region. In general, the EEJ strength is stronger in the west coast of South America than in its east coast. The variability of the EEJ in the dayside ionosphere significantly affects the ionospheric electron density variation, dynamics of the peak height of F2-layer, and TEC distributions as the EEJ influences the vertical transport mechanism of the ionospheric plasma. The eastward electric field (EEF) and the neutral wind play a decisive role in controlling the actual configuration of the EIA. The trans-equatorial neutral wind profile calculated using data from the Second-generation, Optimized, Fabry-Perot Doppler Imager (SOFDI) located near the geomagnetic equator and a physics-based numerical model, LLIONS (Low-Latitude IONospheric Sector) give new perspectives on the effects of daytime meridional neutral winds on the consequent evolution of the asymmetry of the equatorial TEC anomalies during the afternoon onwards. The spatial configurations including the strength, shape, amplitude and latitudinal extension of the EIA crests are affected by the EEF associated with the EEJ under undisturbed conditions, whereas the meridional neutral winds play a significant role in the development of their asymmetric structure in the low-latitude ionosphere. Additionally, the SWARM satellite constellation and the ground-based LISN (Low-Latitude Ionospheric Sensor Network) data allow us to resolve the space-time ambiguity of past single-satellite studies and detect the drastic changes that EPBs and plasma blobs undergo on a short time scale. The coordinated quantitative analysis of a plasma density observation shows evidence of the association of plasma blobs with EPBs via an appropriate geomagnetic flux tube. Plasma blobs were initially associated with the EPBs and remained at the equatorial latitude right above the EPBs height, but later were pushed away from geomagnetic equator towards EIA latitudes by the EPB/ depleted flux tubes that grew in volume. Further, there exists a strong correlation between the noontime equatorial electrojet and the GPS-derived TEC distributions during the afternoon time period, caused by vertical E × B drift via the fountain effect. Nevertheless, only a minor correlation likely exists between the peak EEJ and the net postsunset ionospheric scintillation index (S4) greater than 0.2. This study not only searches for a mutual relationship between the midday, afternoon and nighttime ionospheric phenomena but also aims at providing a possible route to improve our space weather forecasting capability by predicting nighttime ionospheric irregularities based on midday measurements at the equatorial and low latitudes. / Thesis (PhD) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.