Wavelet Analysis of EUV Plasmasphere Maps

J. Cabrera (CSR, FYNU, UCL, Louvain-La-Neuve, France), F. Darrouzet, 
B.R. Sandel, D.L. Gallagher , L. Jacques, J.P. Antoine, J.F. Lemaire

EUV maps of plasmasphere have been analysed using various wavelet numerical
algorithms (Mexican hat Continous Wavelet Transform & Gabor CWT) which have
been developed in IDL language at CSR. The initial goal of this exercise has
been to determine the convection velocities inside the plasmasphere using a
method adapted from Wiskott (1999, Pattern Recognition, 32(10):1751-1766).
The line of sight integrated intensity corresponding to large scale density
irregularities corotating inside the plasmasphere is not sufficient however
to determine by the wavelet method the angular motion and radial velocity of
density irregularities inside the plasmasphere. The EUV images are the
results of averaging five successive scans; this averaging is removing
contrast in the archived EUV images. It might be interesting to investigate
if enough contrast would be there in single scans, so that without onboard
smoothing of EUV maps the wavelet method (or some other numerical algorithm)
would enable the evaluation of the convection velocity inside the
plasmasphere with sufficient resolution. 

Nevertheless, our EUV image analysis has enabled us to develop a software
tool to determine automatically the contours of the plas-mapause defined as
the location where the photometric intensity drops below some adjustable
threshold.  An IDL program has also been built and tested to determine and
archive the radial distance of the plasmapause in any LT direction.

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Presentation at the Yosemite Conference of Inner Magnetospheric Interactions,
3 - 6 February 2004, Yosemite, California, USA