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Ann. Geophys., 16, 1332-1342, 1998
www.ann-geophys.net/16/1332/1998/
© European Geosciences Union 1998
Optical tomography of the aurora and EISCAT
H. U. Frey1,*, S. Frey2,**, B. S. Lanchester3, and M. Kosch4
1Space Sciences Laboratory, University of California, Berkeley CA 94720-7450, USA
2Max-Planck-Institut für Extraterrestrische Physik, D-85740 Garching, Germany
3University of Southampton, Department of Physics, Southampton, SO17 1BJ, UK
4Max-Planck-Institut für Aeronomie, D-37189 Katlenburg-Lindau, Germany
*Former address: MPE Garching
**Present address: Space Sciences Laboratory, UC Berkeley
Abstract. Tomographic reconstruction of the
three-dimensional auroral arc emission is used to obtain vertical and horizontal
distributions of the optical auroral emission. Under the given experimental
conditions with a very limited angular range and a small number of observers,
algebraic reconstruction methods generally yield better results than transform
techniques. Different algebraic reconstruction methods are tested with an
auroral arc model and the best results are obtained with an iterative
least-square method adapted from emission-computed tomography. The observation
geometry used during a campaign in Norway in 1995 is tested with the arc model
and root-mean-square errors, to be expected under the given geometrical
conditions, are calculated. Although optimum geometry was not used,
root-mean-square errors of less than 2% for the images and of the order of 30%
for the distribution could be obtained. The method is applied to images from
real observations. The correspondence of original pictures and projections of
the reconstructed volume is discussed, and emission profiles along magnetic
field lines through the three-dimensionally reconstructed arc are calibrated
into electron density profiles with additional EISCAT measurements. Including a
background profile and the temporal changes of the electron density due to
recombination, good agreement can be obtained between measured profiles and the
time-sequence of calculated profiles. These profiles are used to estimate the
conductivity distribution in the vicinity of the EISCAT site. While the radar
can only probe the ionosphere along the radar beam, the three-dimensional
tomography enables conductivity estimates in a large area around the radar site.
Key words. Tomography · Aurora · EISCAT · Ionosphere
· Conductivity
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