The Sun ionizes a small fraction of Earth's atmosphere above roughly 60 km, producing the plasma that constitutes the ionosphere. Radio signals passing through the ionosphere scatter off of plasma density structures created by the Farley-Buneman instability (FBI). While numerous studies have characterized the FBI's intrinsic nature, its evolution within the broader context of the surrounding plasma remains enigmatic. This dissertation answers two fundamental questions about the FBI: How does it interact with density gradients? How does its non-linear evolution depend on the background plasma? The fourth chapter examines the combined development of the FBI and the gradient drift instability (GDI) using a 2-D simulation of the equatorial ionosphere. A half-kilometer wave perturbs a plasma layer perpendicular to the ambient magnetic field, causing the perturbed layer to develop GDI waves along the gradient aligned with the ambient electric field, as well as FBI waves in a region where the total electric field exceeds a certain threshold. Early radar observations suggested that these two instabilities were distinct phenomena; the reported results illustrate their coupled nature. The fifth chapter presents 2-D simulations in which a one-kilometer plasma wave develops an electric field large enough to trigger meter-scale waves. Such large-scale waves arise via the GDI within the daytime ionospheric gradient around 100-110 km. Typical ionospheric radars only observe meter-scale irregularities but observations show meter-scale waves tracing out larger structures. Simulated meter-scale FBI in the troughs and crests of kilometer-scale GDI matches radar observations of the daytime equatorial ionosphere, answers a question about electric-field saturation raised by rocket observations in the 1980s, and predicts an anomalous cross-field conductivity important to magnetosphere-ionosphere (M-I) coupling. The sixth chapter of this dissertation presents 3-D simulations of the FBI at a range of altitudes and driving electric fields appropriate to the auroral ionosphere, where it plays a role in M-I coupling. Research has thoroughly established the linear theory of FBI but rigorous analysis of radar measurements requires an understanding of the turbulent stage. These simulations explain the change in instability flow direction with altitude, with regard to the direction of background plasma flow.

Após a desativação da disponibilidade seletiva, ocorrida em maio de 2000, a maior fonte de erro presente no sistema GPS passou a ser a refração ionosférica. Os seus efeitos provocam um avanço na fase de batimento da portadora e um atraso no código. Na região equatorial onde o Brasil está inserido, a refração ionosférica apresenta variações que decorrem de diversos fatores tais como: o ciclo solar, o movimento aparente do Sol, as estações do ano, o campo geomagnético, entre outras. Desta forma, a refração ionosférica é um fator limitante pois, degrada a determinação de posições, principalmente, se o usuário estiver utilizando um receptor de apenas uma freqüência. Para avaliar o efeito da refração ionosférica no Brasil, no período compreendido entre janeiro de 1997 a dezembro de 2001, foram utilizados dados coletados com receptores providos de duas freqüências e que integram a Rede Brasileira de Monitoramento Contínuo do Sistema GPS. Todos os dados foram preparados e inseridos em um programa científico de processamento das observáveis do sistema GPS. Devido à grande massa de dados foi necessário o desenvolvimento de um programa para verificar a integridade dos mesmos, converter as efemérides precisas e os dados para o formato de entrada do programa científico e preparar os arquivos de lote. Além das características apresentadas, este programa foi desenvolvido para automatizar o processo de cálculo do conteúdo total de elétrons. Ao final do processamento o programa exibe os parâmetros que representam a refração ionosférica ou seja, os valores calculados para o Conteúdo Total de Elétrons. Tais valores permitiram a criação de uma série histórica do comportamento da refração ionosférica abrangendo um intervalo de tempo que contempla um período em que o ciclo solar apresentava atividade mínima e um outro período em que o ciclo solar alcançou a máxima atividade. Estes dados indicam o comportamento da ionosfera para um período de cinco anos em uma das regiões do planeta que apresenta as maiores variações, comportamento este, que permitirá um melhor conhecimento da ionosfera e a melhoria ou desenvolvimento de modelos mais adequados. Foram gerados ainda, mapas da ionosfera que poderão auxiliar na melhoria da acurácia posicional. / Since the US president decided to turn off the selective availability (SA) one of the biggest error in the GPS system has been the ionosphere refraction. The refraction effect on GPS signals are: delay for the code and an advance for the phase. In the equatorial region, where Brazil is, the refraction presents the biggest variations that are caused by the solar cycle, the time of the day, the season, the geomagnetic field and many others phenomena. In this case, the ionosphere refraction is a limitation because it increases the degradation of the position, specially if the user is using a single frequency receiver. To evaluate the ionospheric effects in Brazil, between January 1997 and December 2001, data from the Brazilian Continuous GPS Monitoring Network were used, provided by double frequency GPS receivers. All data were prepared and used by a scientific software to process the GPS observations. The volume of data was so big that it was necessary to write a software to manage the data integrity, to transform the precise ephemeris and the observations to scientific program format and to create batch files. Also, the program was used to process the data and to compute the total electron content automatically. At the end of the process, the software shows the TEC parameters. These parameters were used to create a historical series of the ionosphere refraction in Brazil. This series represents a period of minimal solar cycle, 1997, and a maximum period of the solar cycle, 2000 / 2001 in one of the most active regions of the planet. This series will improve the knowledge on the ionosphere and will allow to improve models or create new ones. Ionospheric maps that can be used to improve the positional accuracy, were also generated.

Incoherent scatter radar (ISR) systems allow researchers to peer into the ionosphere via remote sensing of intrinsic plasma parameters. ISR sensors have been used since the 1950s and until the past decade were mainly equipped with a single mechanically steerable antenna. As such, the ability to develop a two or three dimensional picture of the plasma parameters in the ionosphere has been constrained by the relatively slow mechanical steering of the antennas. A newer class of systems using electronically steerable array (ESA) antennas have broken the chains of this constraint, allowing researchers to create 3-D reconstructions of plasma parameters. There have been many studies associated with reconstructing 3-D fields of plasma parameters, but there has not been a systematic analysis into the sampling issues that arise. Also, there has not been a systematic study as to how to reconstruct these plasma parameters in an optimum sense as opposed to just using different forms of interpolation. The research presented here forms a framework that scientists and engineers can use to plan experiments with ESA ISR capabilities and to better analyze the resulting data. This framework attacks the problem of space-time sampling by ESA ISR systems from the point of view of signal processing, simulation and inverse theoretic image reconstruction. We first describe a physics based model of incoherent scatter from the ionospheric plasma, along with processing methods needed to create the plasma parameter measurements. Our approach leads to development of the space-time ambiguity function, forming a theoretical foundation of the forward model for ISR. This forward model is novel in that it takes into account the shape of the antenna beam and scanning method along with integration time to develop the proper statistics for a desired measurement precision. Once the forward model is developed, we present the simulation method behind the Simulator for ISR (SimISR). SimISR uses input plasma parameters over space and time and creates complex voltage samples in a form similar to that produced by a real ISR system. SimISR allows researchers to evaluate different experiment configurations in order to efficiently and accurately sample specific phenomena. We present example simulations using input conditions derived from a multi-fluid ionosphere model and reconstructions using standard interpolation techniques. Lastly, methods are presented to invert the space-time ambiguity function using techniques from image reconstruction literature. These methods are tested using SimISR to quantify accurate plasma parameter reconstruction over a simulated ionospheric region.

Certain modern radio systems that rely on trans-ionospheric propagation require knowledge of changes in total electron content (TEC). Understanding rapidly changing, small amplitude perturbations in the ionosphere is important in order to quantify the accuracy of those systems. The main aim of this thesis is to collect statistical information on the perturbations and wave structures present in the ionosphere, for use in radio astronomy calibrations and future communication systems planning. To gain this information, TEC calculated from instruments measuring Faraday rotation on signals from geostationary satellites were used. These measurements were collected in Italy over the period of 19751982 and 1989-1991 at one minute intervals. An important class of TEC fluctuations is travelling ionospheric disturbances (TIDs). Here, temporal variations of mid-latitude slant TEC measurements during two solar cycle phases, i.e solar minimum in 1975-1976 and solar maximum in 1989-1990, were studied. Direct inspection of Savitzky-Golay filtered TEC data was used to extract the amplitudes of TIDs. Fourier analysis was used to extract the most dominant periods of the TIDs. Discrete Meyer wavelet together with the ANOVA method to determine TID variation changes in different parts of the day. Another class of TEC fluctuations presented in this thesis is diurnal double maxima (DDM) structures. These structures were observed during mid-day in our TEC measurements between 1975 and 1991. Verification of the DDM observations was sought by using foF2 and hmF2 measurements from an ionosonde in RomeA combination of ionospheric 3-D tomographic imaging and ray propagation theory has been used for the first time to demonstrate a method that can show how the new European radio array LOFAR will be affected by the ionosphere. This was achieved from a case study of a geomagnetic quiet day ionosphere by simulating how ray propagations, at different elevations and frequencies, will behave as they traverse the ionosphere. The important result from this study was that continuous monitoring of the telescope will be important during operation of the array if the errors introduced by the ionosphere are to be accurately corrected for. The study of TEC changes over different short time windows demonstrated that the ionosphere vastly varies over short time scales, thus making the monitory non trivial. Statistical analysis of the TEC changes will also be useful to the new European GPS augmentation system EGNOS as an indicator on whether the ionospheric measurements from the system are realistic.

This work explores remote sensing of planetary atmospheres and their circumstellar surroundings. The terrestrial ionosphere is a highly variable space plasma embedded in the thermosphere. Generated by solar radiation and predominantly composed of oxygen ions at high altitudes, the ionosphere is dynamically and chemically coupled to the neutral atmosphere. Variations in ionospheric plasma density impact radio astronomy and communications. Inverting observations of 83.4 nm photons resonantly scattered by singly ionized oxygen holds promise for remotely sensing the ionospheric plasma density. This hypothesis was tested by comparing 83.4 nm limb profiles recorded by the Remote Atmospheric and Ionospheric Detection System aboard the International Space Station to a forward model driven by coincident plasma densities measured independently via ground-based incoherent scatter radar. A comparison study of two separate radar overflights with different limb profile morphologies found agreement between the forward model and measured limb profiles. A new implementation of Chapman parameter retrieval via Markov chain Monte Carlo techniques quantifies the precision of the plasma densities inferred from 83.4 nm emission profiles. This first study demonstrates the utility of 83.4 nm emission for ionospheric remote sensing. Future visible and ultraviolet spectroscopy will characterize the composition of exoplanet atmospheres; therefore, the second study advances technologies for the direct imaging and spectroscopy of exoplanets. Such spectroscopy requires the development of new technologies to separate relatively dim exoplanet light from parent star light. High-contrast observations at short wavelengths require spaceborne telescopes to circumvent atmospheric aberrations. The Planet Imaging Concept Testbed Using a Rocket Experiment (PICTURE) team designed a suborbital sounding rocket payload to demonstrate visible light high-contrast imaging with a visible nulling coronagraph. Laboratory operations of the PICTURE coronagraph achieved the high-contrast imaging sensitivity necessary to test for the predicted warm circumstellar belt around Epsilon Eridani. Interferometric wavefront measurements of calibration target Beta Orionis recorded during the second test flight in November 2015 demonstrate the first active wavefront sensing with a piezoelectric mirror stage and activation of a micromachine deformable mirror in space. These two studies advance our ``close-to-home'' knowledge of atmospheres and move exoplanetary studies closer to detailed measurements of atmospheres outside our solar system.

Les séismes de grande magnitude (MW > 7) et les tsunamis associés induisent des perturbations qui peuvent être détectées dans l’atmosphère et l’ionosphère à partir des mesures TEC (contenu total en électron). Dans cette thèse, J’étudie la possibilité d’utiliser ce signal ionosphérique afin de compléter le système de surveillance et d’alerte aux tsunamis. Ainsi, j’étudie le couplage entre la Terre solide, l’océan, l’atmosphère. Je démontre en particulier que seule la fréquence à 1.5 mHz entre les modes de tsunami et les modes de gravité atmosphériques peut être détectée via l’ionosphère et met en évidence que l’efficacité du couplage océan/atmosphère est sensible à la profondeur de l’océan et l’heure locale. Ces développements ont permis de réaliser la modélisation complète de la signature ionosphérique de 3 tsunamis d’amplitude 2, 3 et 60 cm en plein océan : respectivement le tsunami d’Haida Gwaii en 2012 et le tsunami des Kouriles en 2006 en champ lointain et le tsunami de Tohoku 2011 en champ plus proche. Enfin, nous avons démontré que l’amplitude crête à crête de la hauteur du tsunami inversée reconstruit avec moins de 20 % d’erreur l’amplitude mesurée par une bouée DART dans ces trois cas / Large earthquake (MW > 7) and tsunamis are known to induce perturbations which can be detected in the atmosphere and ionosphere using total electron content (TEC) measurements. In this thesis, I first investigated on the possibility of using these ionospheric signals in order to complete the tsunami monitoring and warning system. Thus, I study the coupling between the solid Earth, the ocean, the atmosphere. I demonstrate that only the resonance at 1.5 mHz between the tsunami modes and the atmospheric gravity modes can be detected through ionosphere and highlight the fact that the efficiency of the coupling ocean/atmosphere is sensitive to ocean depth and local time. These developments enables the complete modelling of the ionospheric signature of 3 tsunami with an amplitude of 2, 3 and 60cm in deep ocean: the 2012 Haida Gwaii and the 2006 Kuril tsunami in far field and the 2011 Tohoku tsunami in closer field respectively. Finally, we demonstrated that the peak-to- peak amplitude of the height of the inverted tsunami reconstructs with less than 20% error the amplitude measured by a DART buoy in these three cases

Dynamic Ionosphere Cubesat Experiment (DICE) is a satellite project funded by the National Science Foundation (NSF) to study the ionosphere, more particularly Storm Enhanced Densities (SED) with a payload consisting of plasma diagnostic instrumentation. Three instruments onboard DICE include an Electric Field Probe (EFP), Ion Langmuir Probe (ILP), and Three Axis Magnetometer (TAM). The EFP measures electric elds from 8V and consists of three channels a DC to 40Hz channel, a Floating Potential Probe (FPP), and an spectrographic channel with four bands from 16Hz to 512Hz. The ILP measures plasma densities from 1x104 cm�3 to 2x107 cm�3. The TAM measures magnetic field strength with a range 0.5 Gauss with a sensitivity of 2nT. To achieve desired mission requirements careful selection of instrument requirements and planning of the instrumentation design to achieve mission success. The analog design of each instrument is described in addition to the digital framework required to sample the science data at a 70Hz rate and prepare the data for the Command and Data Handing (C&DH) system. Calibration results are also presented and show fulllment of the mission and instrumentation requirements.

Ionospheric scale height is a measure of the topside altitude dependence of electron density and is a key ionospheric parameter due to its intrinsic connection to ionospheric dynamics, plasma temperature, and composition. A longtime problem has been that information on the bottomside ionospheric profile is readily available, but the observation of the topside ionosphere is still challenging. Despite numerous data techniques to characterize the topside ionosphere, the knowledge of the behavior of the topside ionosphere and its subsequent scale heights remains insufficient. The goal of this study is to evaluate whether or not we can characterize the topside ionospheric density and temperature profiles in the event that neither temperature nor electron density are measured by using a cost-effective method. In a simple model, the electron density in the F-region topside decreases exponentially with height. This exponential decay is mainly driven by thermal diffusive equilibrium, but also dependent on the dominant ion species, as well as other drivers during nondiffusive conditions. A scale height based on observations of the temperature can generate topside electron density profiles. While a measure of the electron density profile enables a scale height to be inferred, hence yielding temperature information. We found a new way to represent how much total electron content (TEC) is allotted for the topside ionosphere. We then used this information to successfully determine TEC using ionosonde data containing only bottomside electron density information. For the first time, slab thickness, which is directly proportional to scale height, was found to be correlated to the peak density height and introduced as a new index, k. Ultimately, k relates electron density parameters and can be a very useful tool for describing the topside ionosphere shape and subsequently, scale height. The methodology of using cost-effective, readily available ionosonde bottomside electron density data combined with GPS TEC was discovered to be capable of inferring the topside ionosphere. This was verified by incoherent scatter radar (ISR) data, though major issues surrounding the availability of ionogram data during nighttime hours greatly limited our study, especially during diffusive equilibrium conditions. Also, significant differences were found between ISR and ionosonde-determined peak density parameters, NmF2 and hmF2, and raised concerns in how the instruments were calibrated.

An important property of the Earth's atmosphere is its ability to support wave motions, and indeed, waves exist throughout the Earth's atmosphere at all times and all locations. What is the importance of these waves? Imagine standing on the beach as water waves come crashing into you. In this case, the waves transport energy and momentum to you, knocking you off balance. Similarly, waves in the atmosphere crash, known as breaking, but what do they crash into? They crash into the atmosphere knocking the atmosphere off balance in terms of the winds and temperatures. Although the Earth's atmosphere is full of waves, they cannot be observed directly; however, their effects on the atmosphere can be observed. Waves can be detected in the winds and temperatures, as mentioned above, but also in pressure and density. In this dissertation, three different studies of waves, known as gravity waves, were performed at three different locations. For these studies, we investigate the size of the waves and in which direction they move. Using specialized cameras, gravity waves were observed in the middle atmosphere (50-70 miles up) over Alaska (for three winter times) and Norway (for one winter time). A third study investigated gravity waves at a much higher altitude (70 miles on up) using radar data from Alaska (for three years). These studies have provided important new information on these waves and how they move through the atmosphere. This in turn helps to understand in which direction these waves are crashing into the atmosphere and therefore, which direction the energy and momentum are going. Studies such as these help to better forecast weather and climate.

The plasma drifts or electric fields and their structures in the ionosphere affect the accuracy of the present-day space-based systems. For the first time, we have used ionospheric plasma drift data from Jicamarca radar measurements to study the climatology of altitudinal variations of vertical and zonal plasma drifts in low latitudes during daytime. We used data from 1998 to 2014 to derive these climatological values in bimonthly bins from 150 km to 600 km. For the vertical plasma drifts, we observed the drifts increasing with altitudes in the morning and slowly changing to drifts decreasing with altitude in the afternoon hours. The drifts change mostly linearly from E- to F-region altitudes except in the morning hours of May-June when the gradients are very small. The zonal drifts show a highly nonlinear increase in the westward drifts at the lower altitudes and then increase slowly at the higher altitudes. We see a break in the slopes at lower altitudes during the morning hours of March-April and May-June. The E-region zonal drifts, unlike vertical drifts, show a very large variability compared to F-region drifts. We also explored the altitudinal profiles of vertical drifts during late afternoon and evening hours when the electrodynamic properties in the ionosphere change rapidly. For the first time using drifts up to 2000 km, we have shown the drifts increase and decrease below and above the F-region peak before becoming height independent. These structures arise to satisfy the curl-free condition of electric fields in low latitudes. The altitudinal gradients of vertical drifts are balanced by a time derivative of the zonal drifts to satisfy the curl-free condition of electric fields. We have shown how these structures evolve with local time around the dusk sector and change with solar flux. During solar minimum, the peak region can go well below 200 km. The present-day electric field models do not incorporate these gradients, particularly in the evening sectors when they change very rapidly. Very often their results do not match with the observations. Including these gradients along with proper magnetic field models will improve the model results and accuracy of our navigation, communication, and positioning systems.