Radio Plasma Imager Simulations and Measurements

J. L. Green, R. F. Benson, S. F. Fung
NASA Goddard Space Flight Center

W. W. L. Taylor, S. A. Boardson
Raytheon Corporation, NASA Goddard Space Flight Center, Greenbelt, MD

B. W. Reinisch, D. M. Haines, K. Bibl, G. Cheney, I. A. Galkin, X. Huang, 
S.H. Myers, AND G.S. Sales
University of Massachusetts, Center for Atmospheric Research, Lowell, MA

J.-L. Bougeret, R. Manning, N. Meyer-Vernet, AND M. Moncuquet
Observatoire de Paris, Meudon, France

D. L. Carpenter
Stanford University, Stanford, CA

D. L. Gallagher
NASA Marshall Space Flight Center, Huntsville, AL

P. H. Reiff
Rice University, Houston, TX


Abstract.  The Radio Plasma Imager (RPI) will be the 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 the dynamics of the magnetosphere and plasmasphere.  RPI will
fly on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE)
mission to be launched early in the year 2000.  The design of the RPI is
based on recent advances in radio transmitter and receiver design and modern
digital processing techniques perfected for ground-based ionospheric sounding
over the last two decades.  Free-space electromagnetic waves transmitted by
the RPI located in the low-density magnetospheric cavity will be reflected at
distant plasma cutoffs.  The location and characteristics of the plasma at
those remote reflection points can then be derived from measurements of the
echo amplitude, phase, delay time, frequency, polarization, Doppler shift,
and echo direction.  The 500 m tip-to-tip X and Y (spin plane) antennas and
20 m Z axis antenna on RPI will be used to measures echoes coming from
distances of several RE. RPI will operate at frequencies between 3 kHz to 3
MHz and will provide quantitative Ne values from 10**-1 to 10**5 cm**-3.

Ray tracing calculations, combined with specific radio imager instrument
characteristics, enables simulations of RPI measurements.  These simulations
have been performed throughout an IMAGE orbit and under different model
magnetospheric conditions. They dramatically show that radio sounding can be
used quite successfully to measure a wealth of magnetospheric phenomena such
as magnetopause boundary motions and plasmapause dynamics. The radio imaging
technique will provide a truly exciting opportunity to study global
magnetospheric dynamics in a way that was never before possible.

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Space Science Reviews, IMAGE Special Issue, Vol. 91, pp. 361-389, February, 2000