Altitude Profiles of Plasma Density in the Trough Region derived from Radio 
Plasma Imager Observations on the IMAGE spacecraft 

T. F. Bell, D. L. Carpenter, U. S. Inan, and B. Reinisch


One of the main objectives of the Radio Plasma Imager (RPI) on the IMAGE 
spacecraft is the observation of the Earth's magnetized plasma from the 
satellite's polar orbit, with apogee of approximately 8 Earth radii and 
perigee near 1200 km altitude. During perigee passes in the trough region 
just poleward of the plasmapause, RPI echoes indicate 200 - 300 kHz HF 
sounding pulses are often ducted to higher altitudes by irregularites near 
the plasmapause surface. The echoes appear in an HF frequency range just 
above the Z mode cutoff at the spacecraft location. Multiple reflections 
occur within these ducts from reflection points  below and above the 
spacecraft, resulting in multiple echoes received on IMAGE. Because the 
multiple echoes allow enhanced time resolution, the apparent range of the 
duct upper reflection point can be determined to a high degree of accuracy. 
Using the range information in conjunction with ray tracing calculations, 
we derive altitude profiles of the cold plasma density in the trough 
region, a region where the characteristics of the cold plasma density are 
poorly known.  

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Fall 2002 Meeting of the American Geophysical Union
San Francisco, CA, USA, 6-10 December 2002