Radio sounding in the Earth's magnetosphere

Abstract

The radio sounding technique has been successfully used for probing and determining the characteristics of remote plasma regions for nearly seventy-five years. Ground-based radio sounders have made extensive measurements of the bottomside of the Earth's ionosphere, while satellites such as ISIS have investigated the topside ionosphere, but there have been no similar measurements made in the Earth's magnetosphere up to this time. Significant advancements in radio sounding have occurred that will enable radio sounding to be performed in the Earth's magnetosphere using the sounding technique. The Radio Plasma Imager (RPI) will be a first-of-its-kind instrument, designed to use radio wave sounding techniques to perform repetitive remote sensing measurements of electron number density (N e ) structures and to study the dynamics of the magnetopause and plasmasphere. RPI will fly on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission, to be launched in the year 2000. RPI will operate at frequencies from 3 kHz to 3 MHz and will provide quantitative N e values from 10 -1 to 10 5 cm -3 . Using ray tracing calculations, combined with specific instrument characteristics, simulations of what RPI will measure dramatically show that radio sounding can be used quite successfully to measure a wealth of magnetospheric phenomena. The radio sounding technique will provide a truly exciting opportunity to study global magnetospheric dynamics in a way that was never before possible.