The streaming plasma in the solar wind is a never ending source of energy, plasma, and momentum for planetary magnetospheres, and it continuously drives large-scale plasma convection systems in our magnetosphere and over our polar ionosphere. This coupling between the solar wind and the magnetosphere is primarily explained by two different processes: magnetic reconnection at high latitudes, which interconnects the interplanetary magnetic field (IMF) with the planetary dipole field, and low-latitude dynamos such as viscous interaction, where the streaming plasma in the solar wind may trigger waves and instabilities at the flanks of the magnetosphere, and thereby allow solar wind plasma to enter into the system.This work aims to further determine the nature and properties of these driving dynamos, both by statistical studies of their relative importance for ionospheric convection at Earth, and by assessment and analysis of the Kelvin-Helmholtz instability at Mercury, utilizing data from the MESSENGER spacecraft's first and third flyby of the planet.It is shown that the presence of the low-latitude dynamos is primarily dependent on the IMF direction: the driving is close to non-existent when the IMF is southward, but increases to the order of a third of the total ionospheric driving when the IMF turns northward (here, the magnitude of the driving is also shown to be dependent on the viscous parameters in the solar wind). The work also discusses the saturation of the reconnection generated potential, and shows that the terrestrial response follows a non-linear behavior for strong solar wind driving both when the IMF is southward and northward.Comparative studies of different magnetospheres provide an excellent path for increasing our understanding of space-related phenomena. Here, study of the Kelvin-Helmholtz instability at Mercury allows us to investigate how the different parameters of the system affect the mass, energy, and momentum transfer at the flanks of the magnetosphere. The large ion gyro radius expected is shown to develop a dawn-dusk asymmetry in the growth rates, with the dawn side as the more unstable of the two. This effect should be particularly visible when the planet is close to perihelion. Mercury's smaller scale size combined with the relatively high spacecraft velocity is also shown to provide excellent opportunities for studying the spatial structure of the waves, and a vortex reconstruction that can explain all the large-scale variations in the Kelvin-Helmholtz waves observed during MESSENGER's third Mercury flyby is presented. / QC 20110405

This thesis gives an outline of the ionosphere and studies that were conducted to investigate / Thesis (M.Sc.) - University of KwaZulu-Natal, 2009.

Incoherent scatter radars are powerful ground based instruments for ionospheric measurements. By analysis of the Doppler shifted backscatter spectrum, containing the signature of electrostatic plasma waves, plasma bulk properties are estimated. At high latitudes the backscattered radar power is occasionally enhanced several orders of magnitude above the thermal backscatter level. These enhancements occur during geomagnetic disturbed conditions and are referred to as naturally enhanced ion acoustic echoes (NEIALs). NEIALs are linked to auroral activity with optical auroral emission observed in the vicinity of the radar measurement volume simultaneously to NEIALs. The backscatter enhancements are thought to be caused by wave activity above thermal level due to instability. A number of theories have been put forward including streaming instabilities and Langmuir turbulence to explain NEIAL observations. NEIALs occur in two classes distinct by their Doppler features. Observations of the first type, which has been studied more extensively, are generally modelled well by the Langmuir turbulence model. The difficulty in trying to understand the driving mechanism of the instability is the limited spatial resolution of the radar measurements. Observations of the second type, reported on more recently, have been interpreted as evidence for naturally occurring strong Langmuir turbulence by means of their Doppler features. Aperture synthesis is a technique to increase the spatial resolution of the radar measurements to below beam width of the single receiver antennas. The technique is employed to investigate the structure of NEIALs in the plane perpendicular to the magnetic field at sub-degree scale corresponding to hundreds of meters to a few kilometres at ionospheric altitudes. Calibration of the radar interferometer is necessary and a calibration technique is presented in paper I. Interferometry observations of a NEIAL event with receivers deployed at the EISCAT incoherent scatter radar on Svalbard are presented in paper II. The size of the enhanced backscatter region is found to be limited to 900 x 500m in the plane perpendicular to the geomagnetic field. These observations constitute the first unambiguous measurements giving evidence for the limited size of the enhanced backscatter region. In paper III observations of strong Langmuir turbulence signatures are presented. The apparent turbulent region in these observations is limited to two narrow altitude regions, 2km extent, and electron density irregularities caused by the turbulence are thought to reach down to decimeter scale length. The turbulence observations were obtained during energetic electron precipitation thereby differing from other observations during which a low energy component in the electron precipitation is reported. In paper IV a statistical study of strong Langmuir turbulence radar signatures is presented. The study reveals differing local time distributions for these signatures from type I NEIALs indicating di_ering driving conditions for the two types of NEIALs. It is found that strong Langmuir turbulence signatures are predominantly observed in the pre-midnight sector where auroral break-up aurora prevails. / <p>QC 20150303</p>

Satellite-based navigation systems make it possible to determine the relative positions of points on the earth with centimetre or even millimetre level accuracy over baselines of up to several thousand kilometres. The highest possible accuracy can only be achieved if the carrier phase integer ambiguities can be resolved. In order to resolve the L1 and L2 integer ambiguities over long GPS baselines, the double difference residual ionospheric errors must be estimated for every satellite, every epoch. The resulting number of parameters is usually too large for estimation using ordinary least squares to be practical due to the time or computing resources needed for the processing. The technique currently used to efficiently estimate the parameters is known as pre-elimination. Pre-elimination divides the unknowns into parameters of interest (the coordinates and ambiguities) and nuisance parameters (the ionospheric path delays). The nuisance parameters are treated as stochastic variables and modelled as process noise, avoiding the need for them to be explicitly estimated. Whilst this approach is highly efficient, it makes assumptions about the stochastic behaviour of the residual ionospheric error that are not necessarily valid. The effectiveness of preelimination can be increased through the use of a deterministic model of the ionosphere. It is the hypothesis of this research that the ionospheric error can be more effectively estimated than is possible with pre-elimination, leading to more reliable ambiguity resolution for long baseline precise positioning. (For complete abstract open document)

Thesis (M.S.)--University of Wisconsin--Madison, 1965. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 30-32.

Thesis (M.Sc. (Physics & Electronics)) - Rhodes University, 2009. / A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (p. 212-223).

An ionospheric topside sounder is a high frequency radar system that is located above the ionosphere, ideally on-board a polar orbiting satellite to provide global coverage. The previous eight satellite sounders have measured the critical frequency of the F2 ionosphere region using traditional swept frequency methods. The most expensive part of these missions however is considered to be the large network of ground support stations required for collecting and processing data. This information has been invaluable in improving our global understanding of the upper ionosphere and the accuracy of critical frequency maps used by HF radio engineers to calculate communications routes and the optimum frequencies for early warning OTH radars. A new technique for the direct detection of critical frequency has been developed, which is called the 'Dispersion Method'. Real data from previous sounders is used in the development and verification of this method. This sounder will not only provide traditional lonograms but detects critical frequency and spread echoes directly from the dispersion of a returning radar pulse. This new method does not use traditional lonograms with their inherent processing complexity and is an order faster than any previous sounder. The 'Dispersion Method' therefore resolves the problems encountered with the past topside sounder missions and produces large quantities of real time data autonomously when required. Previous sounding satellites had little memory capacity, no on-board processing capability, required large antennas and transmitters on satellites with a mass of between 150 and 250 kg. This meant power requirements of about 60 watts per orbit average. A feasibility study to place a third generation topside sounder into low Earth orbit on a 50 kg microsatellite with an orbit average power capacity of only 20 watts has been successfully completed.

Proton cyclotron echoes are phenomena related to the proton cyclotron frequency discovered On topside sounder swept-frequency ionograms from the Canadian satellite Alouette II in 1969. Subsequent studies were also limited to the use of the swept-frequency ionograms and devoted only to these so called regular proton cyclotron echoes. The regular proton cyclotron echoes occur on the swept-frequency ionograms at constant apparent ranges predominantly at frequencies below the electron plasma frequency fN and slightly above the electron cyclotron frequency fH. In this dissertation over 2000 topside sounder ionograms (both swept-frequency mode and fixed-frequency mode) obtained from the Alouette II, ISIS I and II satellites of the Alouette-ISIS program are used to investigate proton cyclotron echoes in detail. Examination of the combined swept-frequency and fixed ionograms indicates that the proton cyclotron echoes are also observed on the fixed-frequency ionograms, In addition to some features, such as constant apparent ranges and higher order multiple echoes, which have been already observed on the swept frequency ionograms and also occur on the fixed-frequency ionograms, under some Conditions non-constant apparent ranges and modulations in intensity of the proton cyclotron echoes on the fixed-frequency ionograms are observed. Usually the proton cyclotron echoes on the fixed-frequency ionogram can be observed for a much longer time than on the swept-frequency ionograms due to the fixed sounding frequencies. A proton cyclotron echo can be under observation for several spin periods of the satellite if the plasma parameters encountered by the sounder are appropriate, The modulation in intensity of the proton cyclotron echo by antenna orientation is evident. In terms of analysis of the combined swept-frequency and fixed-frequency ionograms, and the satellite orbital parameters and spin axis attitude, effects on proton cyclotron echoes of antenna orientation with respect to the earth’s magnetic field are examined. It is found that higher intensity and higher harmonics of proton cyclotron echoes occur when the sounding antenna is parallel to the earth’s magnetic field. A new class of proton cyclotron echoes was discovered, which occur on electron plasma resonances. The proton cyclotron echoes on the fH, nfH (n = 2, 3, 4), fQ3 and fD have been observed- The first three are checked in more detail. The proton cyclotron echoes observed on the fH, 4fH, fQ3 and fD resonances exhibit doublet, on the 2fH resonance triplex and on 3fH resonance single while the regular proton cyclotron echoes are always single. A frequency difference of about 5-10 Hz exists between subechoes in a doublet or triplex. The regular proton cyclotron echo seems to correspond to the first echo of the double or triple proton cyclotron echoes. No echo minus exists and most proton cyclotron echoes on the electron plasm a resonances are observed at dip angles whose magnitudes are less than 8°. This new class of proton cyclotron echoes is attributed to the results of nonlinear interactions of ion and electron Bernstein waves or ion Bernstein waves and DKO mode electromagnetic waves (for the fH resonance). Absorption phenomena on the 3fH, 4fH and fQ3 resonance spikes near the proton cyclotron period on swept-frequency ionograms are observed occasionally, but not yet understood. A theory based on nonlinear interaction of two waves is suggested to interpret proton cyclotron echoes. Many observational features of proton cyclotron echoes can be interpreted by this nonlinear interaction model of two waves. / Graduate

In the last decade, Global Navigation Satellites Systems (GNSS) have gained a significant position in the development of urban navigation applications and associated services. The urban environment presents several challenges to GNSS signal reception, such as multipath and GNSS Line-of-Sight (LOS) blockage, which are translated in the positioning domain in a decreased navigation solution accuracy up to the lack of an available position. For this matter, Vector Tracking (VT) constitutes a promising approach able to cope with the urban environment-induced effects including multipath, NLOS reception and signal outages. This thesis is particularly focused on the proposal and design of a dual constellation GPS + Galileo single frequency L1/E1 Vector Delay Frequency Lock Loop (VDFLL) architecture for the automotive usage in urban environment. From the navigation point of view, VDFLL represents a concrete application of information fusion, since all the satellite tracking channels are jointly tracked and controlled by the common navigation Extended Kalman filter (EKF). The choice of the dual-constellation single frequency vector tracking architecture ensures an increased number of observations and at the same time allowing the conservation of the low-cost feasibility criteria of the mobile user’s receiver. Moreover, the use of single frequency L1 band signals implies the necessity of taking into account the ionospheric error effect. In fact, even after the application of the ionosphere error correction models, a resultant ionospheric residual error still remains in the received observations. The originality of this work relies on the implementation of a dual-constellation VDFLL architecture, capable of estimating the ionosphere residual error present in the received observations. This dissertation investigates the VDFLL superiority w.r.t the scalar tracking receiver in terms of positioning performance and tracking robustness for a real car trajectory in urban area in the presence of multipath and ionosphere residual error.