Green, J. L., S. F. Fung, R. F. Benson, W. W. L. Taylor, Y. Omura, P.
H. Reiff, W. Calvert, D. L. Gallagher, and B. W. Reinisch, Application
of magnetospheric radio imaging techniques to global substorm
dynamics, presented at the Third (3rd) International Conference on
Substorms, Versailles, France, May 13-17, 1996.

Application of Magnetospheric Radio Imaging Techniques to Global 
Substorm Dynamics

J. Green, S. Fung, R. Benson, (Goddard Space Flight Center, Greenbelt,
MD 
 20904), W. Taylor (NRC), Y. Omura (U. of Kyoto),  P. Reiff (Rice) W.
Calvert 
(U of Iowa),  D. Gallagher (MSFC), and B. Reinisch (U of Mass. Lowell)


NASA is considering the use of magnetospheric radio imaging instruments 
on future missions.  The application of the radio imaging technique to
substorm studies is straightforward and has a high potential of obtaining 
unprecedented data on the dynamics of the substorm process. This technique 
is based on more than a half-century heritage of ionospheric sounding 
combined with modern digital processing techniques. Like ionospheric 
sounding, free-space electromagnetic waves from 3 kHz to 3 MHz in 
frequency, launched within the magnetospheric low density cavity will reflect 
specularly at plasma cutoffs. The location and characteristics of the plasma 
at a remote reflection point can be derived from the measurement of the delay 
time and frequency of a returned echo. It has been discovered that when 
ground-based ionospheric sounders operate at specific frequencies, 
characteristic of large scale ionospheric disturbances, sky maps or images 
can be easily produced from the hundreds of echoes measured. In an analogous 
way, images of the magnetosphere at radio frequencies could be obtained.

A magnetospheric radio imager would provide quantitative electron density 
profiles simultaneously in several different directions on a time scale of 
minutes or less.  From an imager situated in the polar cap or lobe, it would
be possible to observe the structure and dynamics of many magnetospheric 
boundaries such as the plasmapause and the magnetopause.  It may also be 
possible, at specific radio frequencies, to image a near-Earth plasmoid and 
thus measure its position, growth, motion and size. Simulations of these 
types of observations will be presented based on specific radio imager
instrument characteristics and extensive ray tracing calculations.