Comparison of various numerical techniques for determining plasma
densities from field aligned echoes observed by RPI/IMAGE 
 
V. Jayanti(1), S. F. Fung (2), X. Huang (3), J. L. Green (2), 
V. Henize (4), W. W. Taylor (1), B. W. Reinisch (3)
 
(1) RITSS/Goddard Space Flight Center, Greenbelt, MD 20771
(2) Goddard Space Flight Center, Greenbelt, MD 20771 
(3) University of Massachusetts Lowell, Lowell, MA 01854 
(4) Rice University MS -108, 6100 S. Main Street, Houston, TX 77005


Plasmagrams from the Radio Plasma Imager (RPI) on the IMAGE satellite often 
show multiple echoes over a common range of frequencies but different 
virtual range regimes. These echo signatures have been interpreted as 
field-aligned echoes. By inverting these echoes a determination of the 
electron density along a field line can be achieved. One can use different 
numerical techniques to compute electron densities along the magnetic field 
line from the observed field-aligned echo traces. The three techniques 
available are 1) field-aligned ray tracing; 2) profile inversion along the 
ray trajectory (Reinisch et al., Geophys. Res. Lett., 28, 4521, 2001); and 
3) power law electron density scaling model. The field-aligned ray tracing 
method uses a background magnetic field model with a variable model 
electron density which are used to compute the group velocity - for a given 
wave mode, wave normal angle  and frequency. We simulate echo trace by 
iteratively modifying the electron density until we get a good match with 
the observed echo trace. The three techniques should in principle give the 
same density profiles within a certain degree of accuracy. In this 
presentation we will compare the results obtained from these three 
techniques and discuss possible sources of error.

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To be presented at the 2002 Spring A.G.U. Meeting, 
Washington, D.C., U.S.A., 28-31 May 2002