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  URSI meeting at Kleinheubach Germany, Wednesday, 8 October 1997
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RADIO PLASMA IMAGER FOR THE EARTH'S MAGNETOSPHERE

Bodo W. Reinisch and RPI Team

Center for Atmospheric Research, University of Massachusetts Lowell, USA

Recently NASA selected the IMAGE satellite mission (Imager for
Magnetopause-to-Aurora Global Exploration) to be launched in January 2000
for the exploration of the Earth's magnetosphere. The Radio Plasma Imager
(RPI) will be one of the instruments flying on IMAGE. For the first time a
digital radio sounder covering the frequency range from 3 kHz to 3 MHz will
be flown in the magnetosphere. The main scientific objective is to observe
the responses of the magnetopause, plasmasphere and the auroral ionosphere
to changes in the solar wind. RPI will complement measurements by optical
(FUV and EUV) and neutral atom imager instruments. The elliptic orbit will
have an apogee of 8 Re and a perigee of 1.2 Re geocentric.
RPI will transmit a maximum of 10 W using two orthogonal 500 m thin wire
dipoles in the spin plane for right and left hand circular polarization.
Antenna tuners enhance the radiation efficiency of the short dipoles. For
reception these antennas will be used together with a 20 m dipole along the
spin axis making it possible to determine the angle of arrival of echo
signals with a resolution of about 2 degree [Calvert et al., Radio Sci.
1997]. Pulse compression and coherent spectral integration (Fourier
analysis) techniques will provide a nominal processing gain of 20 dB so
that the weak echoes can be detected in the presence of AKR noise. This
method of radio imaging is based on the techniques used in the ground-based
Digisonde Portable Sounder [Reinisch et al., Radio Sci., 1997].