Classification of IMAGE/RPI-stimulated plasma resonances and the
determination of magnetospheric electron-density and magnetic-field
values

R. F. Benson, V. A. Osherovich, J. Fainberg, and B. W. Reinisch


The Radio Plasma Imager (RPI) on the Imager for Magnetopause-to-Aurora
Global Exploration (IMAGE) satellite stimulates local plasma resonances.
 A proper classification of these resonances can be used to accurately
deduce both the in situ electron density and the magnetic field strength
even in very tenuous plasmas where the former is difficult to measure. 
Based on many decades of research with ionospheric topside sounders by
many investigators, the resonances observed at the harmonics of the
electron cyclotron frequency fce, the electron plasma frequency fpe, and
the upper-hybrid frequency fuh (where fuh2 = fpe2 + fce2) have been
attributed to the reception of electrostatic echoes of the various
frequency components of the transmitted sounder pulse.  Resonances
observed between the fce harmonics, both above and below fpe, have
different interpretations that involve (in some cases)
sounder-stimulated plasma emissions.  We will show that all of the above
resonances are also observed by RPI in the magnetosphere and we will
demonstrate the importance of using all three of the RPI mutually
orthogonal dipole receiving antennas for investigating them.   In
particular, it will be shown that the classification of the ionospheric
resonances observed between the fce harmonics and below fpe, designated
as the Dn resonances,  also applies to the magnetosphere and provides a
valuable diagnostic tool for the interpretation of high-resolution RPI
plasmagrams  revealing rich plasma-resonance spectra.