Very Low Frequency (VLF) radio waves propagate within the Earth-ionosphere waveguide with very little attenuation. Modifications of the waveguide geometry affect the propagation conditions, and hence, the amplitude and phase of VLF signals. Changes in the ionosphere, such as the presence of the D-region during the day, or the precipitation of energetic particles, are the main causes of this modification. Using narrowband receivers monitoring remote VLF transmitters, the amplitude and phase of these signals are recorded. A multivariate data analysis technique, Principal Component Analysis (PCA), is applied to the data in order to determine parameters such as seasonal and diurnal changes which affect the variation of these signals. Data was then analysed for effects from extragalactic gamma ray bursts, terrestrial gamma ray flashes and solar flares. Only X-rays from solar flares were shown to have an appreciable affect on ionospheric propagation. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2009.

published_or_final_version / Physics / Master / Master of Science

Thesis (M. Sc.)--University of Hong Kong, 1968. / Mimeographed.

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Thesis (M.Sc.)--University of Hong Kong, 1968. / Also available in print.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, Dec. 2004. / Thesis Advisor(s): David C. Jenn. Includes bibliographical references (p. 75-76). Also available online.

This thesis describes the design, construction and results of an accurate, 73 GHz, dual-polarized atmospheric propagation experiment conducted over a 1.8 km total length radar path. The millimetre-wave equipment consisted of a switched-polarization transmitter and a two-channel receiving system which included a phase-compensated crosspolar cancellation network and a novel, high-performance microstrip IF/LO diplexer. Meteorological instrumentation consisted of an improved electrostatic disdrometer, a raingauge network with high temporal and spatial resolution and a three-vector anemometer. A comprehensive experimental model was developed to predict the system crosspolar discrimination (XPD) response during a wide variety of conditions. This model was used to analyze, for what is believed to be the first time, the effects of: orthomode transducer port mismatches, the frequency response and error sensitivity of crosspolar cancellation systems and the range of possible cancelled system XPD responses during rain. This model also led to the development of a phase compensation technique used to improve the stability of the crosspolar cancellation network. The application of the experimental model resulted in far more accurate determinations of path XPD than would have been otherwise possible. The cancelled XPD results showed a reasonable correlation to horizontal wind velocities and agreed with model predictions for effective mean canting angles ranging between 0 and 6°. The frequent observation of negative differential attenuations and erratic uncancelled XPDs led to the conclusion that drops along the path often did not have consistent shapes and canting angles. This is believed to be due to extremely variable wind conditions. Copolar attenuations considerably lower and higher than expected from the standard predictions were observed. The higher attenuations are satisfactorily explained as resulting from vertical wind conditions and are correlated to the predictions from a proposed model which includes the effects of constant vertical wind velocities. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

No description available.

published_or_final_version / Physics / Master / Master of Science