Remote Detection of Small Scale Plasma Density Irregularities in the
Outer Plasmasphere Using the Radio Plasma Imager on the IMAGE 
Spacecraft

Bell, T F,  Spasojevic, M A,  Inan, U S,  Carpenter, D L,  Reinisch, B W

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 soundings of the plasma
from both outside and inside the plasmasphere, RPI echoes are usually
not the discrete traces on range-vs-frequency records (plasmagrams)
that ray tracing simulations predict. Instead they exhibit various
amounts of range spreading, from approximately 0.5 to 2 Earth radii in
virtual range. In the present paper we examine a particular type of
spread echo with ranges between IMAGE and the nominal reflection points
of the waves. Such echoes are commonly found during soundings along
IMAGE orbital segments extending from the plasmapause region to L 2
within the plasmasphere. We consider the possibility that the range
spread may be caused by coherent backscatter of the RPI signal due to
the presence of small scale plasma density irregularities in the region
between the spacecraft and the nominal reflection point of the waves.
Observation of this type of backscatter process can yield information
both on the scale and amplitude of the irregularities.