THEORETICAL INVESTIGATION OF THE COUPLING AND PROPAGATION OF IONOSPHERIC ELF/VLF RADIATION INTO THE EARTH-IONOSPHERE WAVEGUIDE (MODIFICATION, ARECIBO OBSERVATORY, PUERTO RICO)

This document describes a theoretical investigation of the propagation of extremely low frequency/very low frequency ELF/VLF, 1-5 kHz radiation from a source located in the D and lower E regions (60-85 km) of the ionosphere to a remote receiving site on the surface of the earth. It provides theoretical support for analyzing results of past experiments and planning future experiments to create an ELF/VLF communication system using high frequency, (HF), heating modification of ionospheric currents.; Analysis of the HF antenna array at the Arecibo Observatory determined that there was enough power in the sidelobes to modify the ionosphere, thereby creating an ELF/VLF source array. The ELF/VLF frequency response calculated for the ionospheric source array compared well with experimentally measured data.; The coupling of radiation from ionospheric sources into the earth-ionosphere wave guide and the propagation of the radiation to receiving sites are investigated in detail using a model based on reciprocity. The ionospheric sources are located at the geographic coordinates of the Arecibo Observatory and the High Power Auroral Simulation, (HIPAS) HF heating facilities. General characteristics are determined: signal losses are dominated by propagation loss within the wave guide; the least attenuated signal is shown to be 1 kHz; the end-on orientation of the current element results in the strongest radiation; and signals from the ELF/VLF sources above the HIPAS facility suffer more attenuation than those from sources above the Arecibo Observatory facility. The efficiency at 1 kHz of a 70 km altitude end-on source with respect to a vertical, ground-based source was found to be approximately 15% at the HIPAS location; during a polar cap absorption event, (PCA), the efficiency is reduced to 4%. Contour plots of the ELF/VLF magnetic field strengths are presented for both locations, the Arecibo Observatory and the HIPAS facilities.