The Radio Plasma Imager on IMAGE: Measuring Techniques and First Results

B.W. Reinisch, D.M. Haines, I.A. Galkin, X. Huang, Gary Sales, University of 
Massachusetts, Lowell, MA 01854; J.L. Green, R.F. Benson, S.F. Fung, NASA GSFC;  
W.W.L. Taylor, Raytheon ITSS; R. Manning, Observatoire de Paris-Meudon; 
P. Reiff, Rice University; D.L. Carpenter, Stanford University; 
D.L. Gallagher, NASA MSFC.

The radio plasma imager (RPI) on the IMAGE satellite is the first radio sounder ever 
flown in the magnetosphere, and it is the first space-borne sounder that uses modern 
digital processing techniques.. The instrument covers the frequency range from 3 kHz 
to 3 MHz with a receiver bandwidth of 300 Hz. The radiated RF power is limited to 10 
W. RPI uses three orthogonal thin wire antennas, two 500-m tip-to-tip dipoles in the 
spin plane, and a 20-m tip-to-tip dipole along the spin axis. All three antennas are 
used for reception allowing the measurement of the angle of arrival of the signals. 
The long dipoles, which are also used for transmission, are electronically tuned to 
optimize the transmission efficiency. A number of different waveforms can be selected 
to adapt to diverse environments: a simple 3.2 ms pulse modulation with constant 
repetition rate, a complimentary phase-coded pulse consisting of 4 or 8 of the 3.2 ms 
chips, a chirp pulse, and a randomly spaced sequence of 3.2 ms pulses. Selective 
application of pulse compression and Fourier integration processing enhances the 
signal-to-noise ratio by nominally 15 dB. 

The early observations show direct echoes from the plasmasphere, magnetopause, and the 
cusp, and ducted echoes that have propagated over hemispheric distances. The long 
antennas and the very sensitive receivers provide excellent observations in the passive 
receive-only mode when the instrument measures the thermal plasma noise as well as 
natural emissions like the continuum and discrete AKR and the type III solar bursts.

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Presented at the Fall American Geophysical Union Meeting, 
San Francisco, CA., December 15-19, 2000