Thesis (M.S. in Systems Engineeering (Electronic Warfare))--Naval Postgraduate School, December 1990. / Thesis Advisor(s): Adler, Richard W. Second Reader: Jauregui, Stephen. "December 1990." Description based on title screen as viewed on March 30, 2010. DTIC Descriptor(s): Ionosphere, Parameters, Electron Density, Ionospheric Disturbances, Theses, Estimates, Sampling, Value, Measurement, Paths. DTIC Identifier(s): Ionospheric Disturbances, Radio Direction Finders, Atmospheric Refraction, Theses. Author(s) subject terms: Single-Site-Location, Direction-Finding, High-Frequency, Estimation, Sampling. Includes bibliographical references (p. 57-58). Also available in print.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, December 1990. / Thesis Advisor(s): Adler, Richard W. Second Reader: Jauregui, Stephen. "December 1990." Description based on title screen as viewed on March 30, 2010 DTIC Descriptor(s): Polar Regions, Models, Signal To Noise Ratio, Communications Networks, Antennas, Ionospheric Propagation, Value, Statistical Analysis, Noise, Range(Extremes), Field Intensity, Predictions, Level(Quantity) DTIC Identifier(s): Ionospheric Propagation, Mathematical Predictions, High Latitudes, Theses Author(s) subject terms: High Frequency (HF), Ionospheric Propagation. Includes bibliographical references (p. 45). Also available in print.

Thesis--Cornell University. / Without thesis statement. Bibliography: p. 273-278.

Thesis (M.S.)--University of Wisconsin--Madison, 1964. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 49-55.

The present work was initially aimed at providing an explanation for some of the phenomena that occur in the ionosphere at sunrise. The approach that was taken was to determine the changes that take place on a theoretical model of the ionosphere and then to compare these with observations. A prerequisite for this approach was a theoretical model that would show, among other things, a bifurcation of the F layer during daytime without making unjustified arbitrary assumptions. The absence of such a model, particularly as far as non-equilibrium conditions are concerned, resulted in the present attempt to provide such a model for the F1 region.

This dissertation reports research into the theory and practical application of linear frequency modulated ionospheric sounding, as an alternative to the more usual technique of pulse modulation. A comparison of this technique with that of conventional pulse sounders is given, based on the concepts of matched filters and ambiguity functions for both modulations. A theory is developed to relate the group range and phase velocity of the ionospheric target to the phase and frequency of the difference signal at the receiver output. A method is then described whereby the group range and phase velocity of the reflection point as well as the amplitude, arrival angle and polarisation mode of the reflected energy can be measured. A description of the implementation of the technique is given together with some initial results. Finally, some suggestions for improvements are given

Since the Kennelly- Heaviside hypothesis in 1902 of the existence of a partially conducting layer in the upper atmosphere was proved to be true by the experiments of APPLETON and BARNETT (1925) and BREIT and TUVE (1926), this region has become known as the ionosphere. The ionosphere was soon discovered to consist of, not one but several layers (Fig. 1) (i) A layer at a height of just over 100 km. called the E layer. (ii) A layer at a height of approximately 300km. called the F₂ layer. (iii) A layer at a height of approximately 200 km. called the F₁ layer; this layer differs from the other two in that it is only present during the day time in Summer. (iv) Occasional intense reflections from a height of about 100 km. are found - these cannot be attributed to the normal E layer and have received the name "Sporadic E". The presence of two E layers (E₁ and E₂) has been suggested by HALLIDAY (1936) and BEST and RATCLIFFE (l978) but until recently most workers still seem to attribute these reflections to Sporadic E. Recent measurement by rockets of the electron density at E layer heights still do not confirm whether such bifurcation exists in the E region. The diurnal and seasonal variations of the first three layers indicate that the sun is the chief agent in their production. It is generally agreed that these layers consist of ionised molecules or atoms and free electrons produced by radiation from the sun. The origin of Sporadic E ionisation is still obscure, but it is thought that these sudden increases in ionisation which occur in E layer heights are due to passing meteors. Recently it has also been suggested by SEDDON, PICKAR and JACKSON (1954) from rocket measurements that Sporadic E might be due to a steep electron density gradient above the B layer.

Wave-particle interaction in the ionosphere is studied theoretically for wave frequencies around the lower hybrid resonance (LHR) frequency. Expressions are derived by two methods for the growth rate of whistler-mode waves propagating in a magneto-active plasma penetrated by a tenuous beam of nonthermal particles. The first method employs the electrostatic dispersion equation; the second uses the full-wave dispersion equation which reduces to the electrostatic one for large values of refractive index. The equilibrium distribution function for the plasma is Maxwellian, and that for the diffuse streaming particles is also Maxwellian, but is shifted by a streaming velocity parallel to the background magnetic field. The first method assumes that the temperatures are isotropic, while the second assumes that the distributions are characterized by the perpendicular and parallel temperatures, T[subscript: I] and T[subscript: II] . The growth-rate expressions are fairly general, but numerical calculations are performed for the case of a cold plasma consisting of electrons, H⁺ , He⁺ , and 0⁺ ions and a beam of nonthermal electrons. The growth-rate expression obtained using the electrostatic dispersion equation shows that waves propagating slightly off the direction perpendicular to the background magnetic field can grow due to the Landau instability process which is excited by high energy (∼ 10 keV) electrons streaming along the direction of the magnetic field of the earth. The growing wave thus triggered is shown to have a frequency band with a sharp lower cutoff at the LHR frequency and an upper limit at the electron cyclotron frequency or electron plasma frequency, whichever is lower. The previous growth-rate expression is generalized by making use of the full-wave dispersion equation. It is shown that there are two regions in propagation angle 6 where the Landau instability may occur. The "electrostatic" region lies just below the resonant angle and, separated by a region of damping, the "low-θ" region lies above θ = 0 . The growth-rate values calculated in the "electrostatic" region correspond to the values obtained in the previous calculation. Generally, the maximum growth rate is larger in the "electrostatic" than in the "low-θ" region. It is also seen that with increasing frequency the "electrostatic" maximum growth rate increases monotonically and the cyclotron instabilities become important at frequencies above about ten times the LHR frequency. The influence of the following parameters on the growth rate is also examined: temperature ratio T[subscript: II]/T[subscript: I], streaming velocity of the nonthermal particles, and the ratio of the kinetic energy in the streaming motion to the thermal energy of the streaming electrons. The theory presented is applied to LHR noise bands discovered by the Canadian Alouette I satellite. It is shown that many features are in good agreement. Other observations, such as auroral hiss, also have features which suggest that the theoretical work may be relevant to these types of ionospheric noise. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Two possible ionospheric electric currents for Pi2 micropulsations are investigated and tested against data collected from a meridian chain of stations in Saskatewan. The electric coupling between the ionosphere and the magnetosphere under disturbed magnetospheric conditions is believed to be the cause of the Pi2 generation and propagation. The LC circuit analogy is first used to model this interaction, the source of energy lying in the magnetospheric equatorial plane. Secondly, the possibility of an ionospheric electric impulse imparted to a field-aligned current under the conditions of brightening of aurora is considered. It is found experimentally that the Pi2 originates possibly from these two source regions: the characteristics of a resonant LC oscillation expanding symmetrically to the west and to the east of the magnetospheric potential source are observed, as well a strong toroidal field existing and possibly originating in the ionosphere. It is suggested that optical data in conjunction with auroral radar echo and satellite data be necessary to confirm a future mathematical development of these possible Pi2 generation and propagation models. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Super Dual Auroral Radar Network (SuperDARN) data is a powerful tool for space science research. Traditionally this data has been processed using a routine with known limitations. A large issue preventing the development and implementation of new processing algorithms was the lack of a realistic test dataset. We have implemented a robust data simulator based on physical principles which is presented in Chapter 2. The simulator is able to generate SuperDARN data with realistic statistical fluctuations and known input Doppler velocity and spectral width. Using the simulator to generate a test data set, we was able to test new algorithms for processing SuperDARN data. The algorithms which were tested included the traditional method (FITACF), a new approach using the bisection method (FITEX2), and the Levenberg-Marquardt algorithm for nonlinear curve fitting (LMFIT). FITACF is found to have problems when processing data with high (> 1~km/s) Doppler velocity, and is outperformed by both FITEX2 and LMFIT. LMFIT is found to produce slightly better fitting results than FITEX2, and is thus my recommendation to be the standard SuperDARN data fitting algorithm. The construction of the new midlatitude SuperDARN chain has revealed that nighttime, quiet-time plasma irregularities with low Doppler velocity and spectral width are a very common (> 50% of nights) occurrence. Following on previous work, we have conducted a study of nighttime midlatitude convection using SuperDARN data. First, the data are processed into convection patterns, and the results are presented. The drifts are mainly zonal and westward throughout the night. The plasma drifts also display significant seasonal variability. Additionally, a large latitudinal gradient is observed in the zonal velocity during the winter months. This is attributed to processes in the conjugate hemisphere, and possible causes are discussed. During my graduate studies, we have been part of the development of a software package for enabling and accelerating space science research known as DaViTpy. This software package is completely free and open source. It allows access to several different space science datasets through a single simple interface, without having to write any code for reading data files. It also incorporates several space science models in a single install. The software package represents a paradigm shift in the space science community, and is presented in Appendix A. / Ph. D.