Simulations of Radio Imaging in the Earth's Magnetosphere J L Green, S Boardsen, W W L Taylor, S F Fung, R F Benson (All at NASA/Goddard Space Flight Center, Greenbelt, MD); B W Reinisch (University of Massachusetts, Lowell, Lowell, MA); Dennis Gallagher (NASA/Marshall Space Flight Center, AL) The New Millennium Magnetosphere: Integrating Imaging, Discrete Observations, and Global Simulations, Sixth Huntsville Modeling Workshop, Guntersville, Alabama, 26-30 October 1998. The Radio Plasma Imager (RPI) will be a first-of-its-kind instrument designed to use radio wave sounding techniques to perform high-resolution measurements of the structure and dynamics of the electron density (Ne) in the Earth's magnetosphere. RPI will fly on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission to be launched in the year 2000. The design of the RPI is based on the recent advances in radio transmitter and receiver design, and modern digital processing techniques perfected for ionospheric sounding over the last two decades. Electromagnetic waves transmitted by the RPI from 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 delay time, frequency, Doppler shift, and direction of an echo. The 500 m tip-to-tip X and Y (spin plane) antennas and 20 m tip-to-tip Z axis antenna on RPI will be used to measures echoes coming from perhaps as great as 10 RE. RPI will operate at frequencies between 3 kHz to 3 MHz and will provide quantitative Ne values from 0.1 to 105 cm-3. Using ray tracing calculations, combined with specific radio imager instrument characteristics, enables simulations of what RPI will measure. These simulations have been performed from various vantage points along a typical IMAGE orbit and under different model magnetospheric conditions. The simulation results dramatically show that radio sounding observations can reveal a wealth of information on the global-scale magnetospheric structure. The radio imaging technique will provide a truly exciting opportunity to study global magnetospheric dynamics in a way which was never before possible.