Radio Sounding in the Earth's Magnetosphere

J. L. Green (1), R. F. Benson (1), S. F. Fung (1), W. W. L. Taylor (2), 
S. A. Boardsen (2), and B. W. Reinisch (3)

(1) NASA Goddard Space Flight Center, Greenbelt, Maryland
(2) Raytheon, NASA Goddard Space Flight Center, Greenbelt, Maryland
(3) Center for Atmospheric Research, University of Massachusetts, Lowell, Massachusetts

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 (Ne) 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 Ne 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.

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in Radio Astronomy at Long Wavelengths, Geophysical Monograph, vol. 119, 
edited by R. G. Stone, K. W. Weiler, M. L. Goldstein, & J.-L. Bougeret, 
pp. 359-372, American Geophysical Union, Washington, 2000.