Fung, S. F., and J. L. Green, Radio imaging of plasmaspheric structure
by RPI on IMAGE, presented at the American Geophysical Union Fall
Meeting, San Francisco, December 15-19, 1996.

Radio Imaging of Plasmaspheric Structure by RPI on IMAGE

S. F. Fung and J. L. Green, NASA GSFC Greenbelt, MD 20771}  

   This paper investigates the use of radio sounding to observe the structure
of the plasmasphere. Radio sounding techniques, which had been well developed
for ionospheric studies, can be applied to probe the structure and dynamics of
magnetospheric structures such as the magnetopause, plasmapause and
plasmasphere. Unlike in situ spacecraft observations which provide only local
measurements, omni-directional radio sounding measurements made within the
low-density magnetospheric cavity can be used to image the global plasmaspheric
structure and its surrounding plasma components, such as a "tongue" or a
detached plasma region. The high time resolution of radio sounding
measurements, when correlated with other global imaging observations, will
yield much information on the dynamics of the plasmasphere as a function of
geomagnetic storm and substorm phases. This is indeed one of the science
objectives of the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE)
mission, selected recently by NASA as the first Mid-size Explorer mission to be
launched in January 2000. IMAGE will carry a complement of instrumentations for
radio, neutral-atom, FUV and EUV imaging. The radio sounder on IMAGE is called 
the Radio Plasma Imaging (RPI) instrument.
   Using three-dimensional ray tracing calculations in a model
magnetosphere,
multi-frequency RPI echoes from the plasmapause and plasmasphere are simulated.
Images of the plasmapause are obtained at single frequencies. The
characteristic knee of the plasmapause is easily found in delay time vs.
frequency plasmagrams, obtained by simulating the resulting echoes from a
characteristic frequency sweep of the RPI instrument. These and other unique
plasmaspheric signatures in the simulated data will be discussed.