INVESTIGATION OF LOWER D-REGION BY USING VLF ATMOSPHERICS

Abstract

The earliest experiment on ionospheric propagation of very long radio waves) even before the pulse sounding was discovered, appears to have been carried out by Hollingwarthi( ,926)in England. He measured the field strength laid down by a broad cast transmitter radiating on 20.9 KHz at different distances and thereby studied • the spatial distribution of the interference pattern caused by the sky wave and ground wave. He deduced from the experiment that the wave was being reflected during a summer day from a height of about 75 Km. Since then a• large number of investigations and experiments have been carried out by many workers in different parts of the world- on the propagation through D-region of very long and long waves. Demars2 (1930), Tokoyava and Mamba (19 32) and Tokoyava and Janimara (1932) have carried out fairly exhaustive study of propagation of VLF and LF waves at large distanees.'1'hey concluded from their investigations that for a homogenous medium, the Brewster angle 0, depends on electron density N, collision frequency and the angular wave frequency w. If >> w, the medium behaves like a metallic reflector and 0 is nearly 900 i.e. grazing incidence