RPI Sounding of the Plasmasphere: Comparison of Measurement and Simulation

Spasojevic, M. A., U. S. Inan, D. L. Carpenter, T. F. Bell, J. Goldstein,
B. W. Reinisch

The Radio Plasma Imager (RPI) on the IMAGE spacecraft uses radio sounding
techniques to probe the plasma environment in the Earth's magnetosphere.
During soundings of the steep density gradients in the vicinity of the
plasmapause and throughout most of the main body of the plasmasphere, RPI
echoes are usually not in the form of discrete traces on 
range-vs.-frequency records (plasmagrams) that were predicted by pre-launch
ray tracing simulations. Instead they exhibit various amounts of range
spreading, from approximately 0.5 to 2 Earth radii in virtual range. Much
of the spread in range of returning echoes is attributed to scattering from
density irregularities. In order to investigate possible scattering
mechanisms, it is first necessary to determine where the nominal reflection
point (distance at which the wave frequency is equal to the cut-off
frequency) lies with respect to the range of the returning scattered
signal. We will present results of 2-D ray tracing simulations of both the
ordinary and extraordinary wave modes corresponding to specific RPI
measurements. For each case studied, the electron density model used for
the ray tracing is scaled to match the in-situ density profile extracted
from the dynamic spectra at points along the orbit.

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To be presented at the Magnetospheric Imaging Workshop, 
Yosemite National Park, California, U.S.A., Feb. 5-8, 2002.