First Results from the Radio Plasma Imager on the IMAGE Mission 

B. Reinisch (1), and the RPI Team

1 - University of Massachusetts, Lowell, MA, USA

The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission was
successfully launched on March 25, 2000. IMAGE was placed into a polar orbit
with apogee of about 7 Earth radii (RE) and inclination of about 45 degrees.
The Radio Plasma Imager (RPI) on IMAGE is a radio sounder designed to sweep
from 3 kHz to 3 MHz. Radio plasma imaging uses total reflection of
electromagnetic waves from plasmas whose plasma frequencies equal the radio
sounding frequency and whose electron density gradients are parallel to the
wave normals. The RPI has two orthogonal 500-m long dipole antennas in the
spin plane for transmission and reception. The spin axis antenna is a 20-m
dipole for reception only. Echoes from magnetospheric boundaries and plasma
regions have been received on all three orthogonal antennas, allowing the
determination of the angle-of-arrival of the echoes. RPI has been operating
in three active sounding modes: (1) remote sounding to probe magnetospheric
boundaries, (2) local (relaxation) sounding to probe the local plasma, and
(3) whistler stimulation sounding. In addition, there is a passive mode to
record natural emissions, and to determine the local electron density and
temperature by using a thermal noise spectroscopy technique. On the IMAGE
mission, RPI is well situated to observe the structure and dynamics of a number
of magnetospheric boundaries over periods of several hours during geomagnetic
storms. This paper will provide an overview of the early measurements from the
RPI instrument during many of its operating modes.

The application of remote sensing techniques has a high potential of obtaining
unprecedented space weather related data on the dynamics of storm and substorm
processes and in particular determining the relationship between a variety of
phenomena.

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Submitted to Geophysical Research Letters, IMAGE special issue, September 2000