Magnetospheric electron-density determinations from emissions in the
upper-hybrid band observed by RPI on IMAGE

P. A. Webb (Nomad Res. Inc.), R. F. Benson, J. L. Green and L. Garcia (QSS)
NASA/Goddard Space Flight Center

R. Denton Dartmouth College

J. Goldstein SWRI

B. W. Reinisch University of Massachusetts Lowell

The electron density Ne is often derived from an intense narrowband
emission, identified as the upper-hybrid band, on passive radio-wave dynamic
spectra. The derivation is usually based on the assumption that the
frequency of the maximum amplitude fmx of this emission either corresponds
to the electron plasma frequency fpe or the upper-hybrid frequency fuh =
(fpe^2 + fce^2)^1/2 where fce is the electron cyclotron frequency.  The 
Radio Plasma Imager (RPI) on the Imager for Magnetopause-to-Aurora Global
Exploration (IMAGE) satellite was used to investigate the relationship of
fpe and fuh (determined from active soundings) to fmx and to the lower and
upper frequency edges of the emission enhancement, flo and fup,
respectively. It was found that flo corresponds to the larger of fce and
fpe, that fmx typically occurred between fpe and fuh, and that fup = fuh.
These active/passive comparisons provided the backdrop for establishing an
automated technique for extracting Ne values from passive dynamic spectra
with a degree of confidence.  While this technique will be demonstrated with
RPI data, it promises to have valuable applications to other data sets from
planetary magnetospheres where the luxury of active/passive comparisons may
not be available.

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Presentation at the 35th COSPAR Scientific Assembly, Paris, France, 
18 - 25 July 2004