Radio Tomography Experiments with IMAGE, WIND, and Cluster

S.A. Cummer, J.L. Green, B.W. Reinisch, M.L. Kaiser, M.J. Reiner, 
R. Manning, K. Goetz, I. Christopher, R. Mutel, J. Pickett, 
D.A. Gurnett, and P. Escoubet


To validate and demonstrate the potential of magnetospheric radio
tomography, we have performed three separate experiments using the
Radio Plasma Imager (RPI) on the IMAGE spacecraft as the signal
source.  The WAVES instrument on WIND and the WBD instruments on the
four Cluster spacecraft were used as the wave receivers.  These
experiments were designed to measure the Faraday rotation of the
transmitted wave electric field polarization due to propagation
through a magnetized plasma.  In the proper frequency range, Faraday
rotation is proportional to the path-integrated product of the
magnetospheric electron density and magnetic field, enabling
large-scale measurements of these quantities on the propagation paths
in each of these experiments.  In August 2000, WAVES received a
single frequency (828 kHz) RPI transmission.  In October through
December 2001, WAVES received two frequency (508 and 828 kHz) RPI
transmissions.  And in April 2002, WBD on Cluster received stepped
frequency (between 100 and 500 kHz) RPI transmissions.  Some of the
RPI signals have been measured on propagation paths longer than 10
Re. By exploiting the time variation and frequency dependence of
Faraday rotation, the integrated electron density/magnetic field
product has been measured, with some limitations, in each of these
experiments. We report on the novel large scale measurements of
magnetospheric plasma and magnetic field generated by each of these
radio propagation experiments.  We also demonstrate, through these
measurements, what quantities can be measured and how best to measure
them on a dedicated radio tomography mission. These experiments have
also shown that magnetospheric radio tomography can be implemented
with existing instrument technology.

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URSI Meeting, Cleveland, Ohio, June, 2003