Reiff, P. H., B. W. Reinisch, J. L. Green, S. F. Fung, R. F. Benson, M. F. Smith, W. W. L. Taylor, D. L. Gallagher, W. Calvert, and D. L. Carpenter, Radio plasma imaging: opportunities and challenges, presented at the American Geophysical Union Fall Meeting, San Francisco, December 15-19, 1996. Radio Plasma Imaging: Opportunities and Challenges Patricia H. Reiff, B. W. Reinisch, J. L. Green, S. F. Fung, R. F. Benson, M. F. Smith, W. W. L. Taylor, D. L. Gallagher, W. Calvert, and D. L. Carpenter The Radio Plasma Imager (RPI) on IMAGE brings a new type of measurement to the high latitude magnetosphere: active radio sounding of the magnetopause, cusp, and plasmasphere. In this experiment, selected to fly as part of the IMAGE mission, a sequence of coded radio bursts are transmitted isotropically and the received echoes analyzed in terms of amplitude, polarization, angle of return, Doppler shift, and round-trip time. The signals are reflected back to the receiver from remote plasma structures where the local plasma frequency equals the transmitted frequency, and where the local density gradient is essentially parallel to the line of sight from the spacecraft. For a smooth near-parabolic magnetopause, the signal is returned from one principal reflection point; for a wavy surface, several returns from various directions are possible. Using digital integration and tuned reception at frequencies from a few kilohertz to a few megahertz with 400m to 500m tip-to-tip dipole antennas and 10W transmitter power, such a sounder would be capable of 10% density resolution and 500 to 1300 km spatial resolution in only a few minutes at distances of up to 4 Re. By providing such detailed observations of its principal density structures, such a sounder heralds the first remote sensing of the plasmasphere and the magnetopause at distances larger than an ion gyroradius. The technique is not without challenges, however, and several difficulties will be introduced here but will be discussed in more detail in companion presentations.