Whistler and Z-mode echoes from radio sounding of the IMAGE satellite

D. L. Carpenter 1, V.S. Sonwalkar 2, T. F. Bell 1, M. A. Spasojevic 1, U.S. Inan 1, 
R. F. Benson 3, B. W. Reinisch 4

1 Space, Telecommunications and Radioscience Laboratory, Stanford University, Stanford, CA
2 Department of Electrical Engineering, University of Alaska Fairbanks, Fairbanks, AK
3 NASA Goddard Space Flight Center, Greenbelt, MD
4 Center for Atmospheric Research, University of Massachusetts Lowell, Lowell, MA

When the Radio Plasma Imager (RPI) on the IMAGE  satellite operates in the inner 
plasmasphere and at moderate to low altitudes over the polar regions, pulses 
emitted at the low end of its 3 kHz to 3 MHz sounding frequency range can propagate 
in the whistler mode or in the L-X/Z mode. During soundings with both 51.2 ms 
pulses and 3.2 ms pulses, whistler mode echoes have been observed both in discrete, 
lightning-whistler-like forms, and in diffuse forms indicative of mode coupling at 
the boundaries of density irregularities. Both of these types of echoes have 
potential for diagnostics of plasma distributions and structures. The L-X/Z mode is 
strongly excited during medium to low altitude portions of most IMAGE orbits. It is 
helpful in identifying local plasma parameters such as the upper hybrid resonance 
and the plasma frequency under conditions when those frequencies are not well 
defined in passive recordings, and may also be usable as a probe of the density 
distribution near the satellite as well as the occurrence and size of density 
irregularities.  Future challenges include efforts to transmit whistler-mode signals 
to ground points and spacecraft of opportunity and investigations of interactions 
between whistler-mode waves and energetic electrons. 

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To be presented at the Magnetospheric Imaging Workshop, 
Yosemite National Park, CA, Feb. 5-8, 2002.