First Observations by the Radio Plasma Imager (RPI) on IMAGE

S. F. Fung (1), R. F. Benson (1), J. L. Green (1), B. W. Reinisch (2), 
D. M. Haines (2), I. A. Galkin (2), G. S. Sales (2), X. Huang (2), 
J.-L. Bougeret (3), R. Manning (3), P. H. Reiff (4), D. L. Carpenter(5), 
D. L.  Gallagher (6), and W. W. L. Taylor (7)

1 NASA Goddard Space Flight Center, Greenbelt, MD
2 University of Massachusetts, Lowell, MA 
3 Observatoire de Paris, France
4 Rice University, Houston, TX
5 Stanford University, Palo Alto, CA
6 NASA Marshall Space Flight Center, Huntsville, AL
7 Raytheon ITSS Corporation, Lanham, MD


The Radio Plasma Imager (RPI) is the first digital radio sounder designed 
to perform long-range radio sounding of the magnetosphere. Launched on 
March 25, 2000 aboard the Imager for Magnetopause-to-Aurora Global 
Exploration satellite (IMAGE, see http://image.gsfc.nasa.gov), the RPI 
began routine operations after the full deployment of its three-axis 
dipole antenna system on May 14, 2000, making both active sounding and 
passive observations in different magnetospheric plasma regions. The RPI 
transmits (20 W maximum) and receives radio pulses from 3 kHz to 3 MHz 
(corresponding to plasma densities of 0.1-10**5 cm-3). Together with the 
two 500-m tip-to-tip spin-plane dipoles, a 20-m tip-to-tip spin-axis 
dipole antenna is used for echo reception. RPI employs digital pulse 
compression and spectral integration techniques in order to detect 
long-range echoes characteristic of magnetospheric sounding. The RPI has 
observed direct echoes from the polar cap, polar cusp, plasmapause, and 
the magnetopause. In addition, strong ducted echoes have been observed 
near the plasmapause boundary, whistler mode echoes are commonly observed 
from deep within the plasmasphere, and plasma resonances are stimulated at 
the local electron gyroharmonic frequencies and others. RPI passive 
observations of natural emissions have produced spectrograms that reveal 
unprecedented details of low-density plasma structures. This paper will 
highlight these exciting early RPI observations. 

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Presented at the Seventh Huntsville Workshop -
A New View of Geospace: Integration, Interpretation and Synthesis
October 30 - November 3, 2000, Callaway Gardens, Georgia