Opportunities for passive VHF radar studies of plasma irregularities in the equatorial E and F regions

Abstract

Commercial FM broadcasts near 100 MHz provide powerful illumination of the ionosphere at a very useful wavelength. By performing synchronous observation of the transmitted signal and of scatter from the ionosphere, it is possible to produce excellent range and Doppler maps, and with additional antennas, interferometry may also be performed. Passive VHF radar has been successfully deployed at high latitudes to study auroral E region irregularities. At high latitudes the magnetic field geometry and strongly field-aligned nature of the irregularities restrict coherent scatter to the E region only, and only then near the poleward horizon. At the equator, however, these geometric issues permit observation of the E and F regions. Here we review the basic technique of passive radar, show some high latitude observations, and then lay out the scientific and experimental case for performing similar observations near the Earth's equator.