First results from the Radio Plasma Imager on IMAGE
B. W. Reinisch (1), X. Huang (1), D. M. Haines (1), I. A. Galkin (1), J. L. Green (2), 
R. F. Benson (2), S. F. Fung (2), W. W. L. Taylor (3), P. H. Reiff (4), D. L. Gallagher (5), 
J.-L. Bougeret (6), R. Manning (6), D. L. Carpenter (7) and S. A. Boardsen (8)

1 Center for Atmospheric Research, University of Massachusetts, Lowell, MA
2 NASA Goddard Space Flight Center, Greenbelt, MD
3 Raytheon ITSS Corporation at NASA Goddard Space Flight Center, Greenbelt, MD
4 Rice University, Houston, TX 
5 NASA Marshall Space Flight Center, Huntsville, AL
6 Observatoire de Paris, Meudon, France
7 STAR Laboratory, Stanford University, Stanford, CA
8 Emergent Information Technologies, Inc. at NASA Goddard Space Flight Center, Greenbelt, MD

The Radio Plasma Imager (RPI) is a 3 kHz to 3 MHz radio sounder, incorporating modern digital 
processing techniques and long electronically-tuned antennas, that is flown to large radial 
distances into the high-latitude magnetosphere on the Imager for Magnetopause-to-Aurora Global 
Exploration (IMAGE) satellite.  Clear echoes, similar to those observed by ionospheric topside 
sounders, are routinely observed from the polar-cap ionosphere by RPI even when IMAGE is 
located at geocentric distances up to approximately 5 Earth radii.  Using an inversion 
technique, these echoes have been used to determine electron-density distributions from the 
polar-cap ionosphere to the location of the IMAGE satellite.  Typical echoes from the 
plasmapause boundary, observed from outside the plasmasphere, are of a diffuse nature 
indicating persistently irregular structure.  Echoes attributed to the cusp and the 
magnetopause have also been identified, those from the cusp have been identified more often 
and with greater confidence.

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Geophysical Research Letters, Vol. 28, No. 6, pp. 1167-1170, March 15, 2001