The absorption of a radio wave propagated through the ionosphere at oblique incidence, depends fundamentally, on the height distributions of electron density and the coUisional frequency of the electrons with the neutrail gas atoms. The vciriation of the electron density with height will also determine the paths along which the radio energy flows. Experimental observations have been made of the absorption losses and of the various modes of propagation over four oblique incidence paths, of lengths between 500 and 1000 km. The seasonal, diurnal and anomalous variations in these data have been discussed. The experimental observations have also been used to test the validity of the theoretical results of prediction and ray tracing analyses. The prediction of path parameters, such as mode structure and absorption, is important in the design of broadcasting circuits and the basic equations and assumptions of these methods are discussed in detail in an attempt to determine the accuracy of these procedures. The predicted conditions for the four test circuits have been compared with experimentally observed values. At oblique incidence, the absorption can be calculated by use of ray tracing; methods. A computer program, based on the Booker equations, was written so that the absorption on the oblique paths could be evaluated for a range of electron density models. This program was compared with other standard ray tracing methods for both experimental and analytical models of the ionosphere and the results were found to be in excellent agreement. The ray tracing results were also compared with the experimental data in order to establish the validity of the ionospheric models. Composite models consisting of published D region distributions and experimentally derived E and F regions were found to give results in good agreement with experiment. Absorption data for several oblique and vertical incidence paths was available 'for 1966 and a correlation analysis of these results has been carried out. Marked similarities were evident; a result which is important when predicting path parameters for one oblique circuit from measurements made on another. Absorption variations during ionospheric disturbeoices have also been studied and compared with steep incidence VLF results. The enhanced electron density during these periods appears, in most cases, to be located at heights above 75-80 km. This study has revealed that ray tracing and prediction methods, when applied to oblique incidence circuits of up to.;000 km. in length, can yield resultswhich are consistent with experimental observations of absorption and angle of arrival for such circuits.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:673954 |
| Date | January 1968 |
| Creators | Keenliside, William |
| Publisher | University of Leicester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/2381/35708 |
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