Calvert, W., R. F. Benson, D. L. Carpenter, S. F. Fung, D. L.
Gallagher, J. L. Green, P. H. Reiff, B. W. Reinisch, M. F. Smith, and
W. W. L. Taylor, Radio sounding of the earthıs magnetosphere, URSI
meeting, Boulder, CO, Jan. 3-7, 1995.

RADIO SOUNDING OF THE EARTH'S MAGNETOSPHERE

W. Calvert, R. F. Benson, D. L. Carpenter, S. F. Fung, D. L.
Gallagher, J. L. Green, P. H. Reiff, B. W. Reinisch, M. F. Smith, and
W. W. L. Taylor c/o W. Calvert Department of Physics and Astronomy
University of Iowa, Iowa City. IA 52242


Radio sounding in the Earth's magnetosphere would provide remote
density measurements of unprecedented precision and coverage, yielding
important new information about the structure, relationship, and
variations of its different plasma regions.  Using ray tracing and
wave theory, we have investigated the echo properties of the
magnetosphere for a satellite radio sounder located in the
magnetospheric cavity outside the plasmasphere.  We have constructed
density models for the plasmasphere, magnetopause, and cusp based on
previous satellite measurements of local density, and calculated the
direction, echo power flux, and delay of the echoes which they produce
at frequencies of 30 to 300 kHz.  We have also analyzed focusing and
defocusing by curved surfaces, investigated the echoes produced by
large-scale density irregularities at the magnetopause, and examined
the nature of spread echoes at the plasmapause and magnetopause.

For a sounder using three orthogonal antennas to measure echo
directions, the angular precision, in radians, equals twice the
reciprocal signal-to-noise ratio, and as a consequence, the volume
resolution remains constant as the pulse length and bandwidth are
varied to change the range resolution.  Using pulse compression and
spectral integration, a 10-watt sounder with 500-meter transmitting
antennas would produce a signal-to-noise ratio of a hundred or more
for echoes from the magnetopause, plasmapause, and plasmasphere at 30
to 300 kHz in about 3 minutes, using 5% frequency steps, a 300 Hz
receiver bandwidth, and 3.3 msec sounding pulses.  This then implies
1š angular precision, and hence 500 km spatial resolution in all three
directions at a distance of 4 Earth radii.