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Ann. Geophys., 16, 1180-1189, 1998
www.ann-geophys.net/16/1180/1998/
© European Geosciences Union 1998
Application of tomographic inversion in studying airglow in the mesopause region
T. Nygrén1, M. J. Taylor2, M. S. Lehtinen3, and M. Markkanen3
1Department of Physical Sciences, University of Oulu, FIN-90570 Oulu, Finland
2Space Dynamics Laboratory and Physics Department, Utah State University, Logan, UT, 84322, USA
3Sodankylä Geophysical Observatory, FIN-99600 Sodankylä , Finland
Abstract. It is pointed out that observations of
periodic nightglow structures give excellent information on atmospheric gravity
waves in the mesosphere and lower thermosphere. The periods, the horizontal
wavelengths and the phase speeds of the waves can be determined from airglow
images and, using several cameras, the approximate altitude of the luminous
layer can also be determined by triangulation. In this paper the possibility of
applying tomographic methods for reconstructing the airglow structures is
investigated using numerical simulations. A ground-based chain of cameras is
assumed, two-dimensional airglow models in the vertical plane above the chain
are constructed, and simulated data are calculated by integrating the models
along a great number of rays with different elevation angles for each camera.
After addition of random noise, these data are then inverted to obtain
reconstructions of the models. A tomographic analysis package originally
designed for satellite radiotomography is used in the inversion. The package is
based on a formulation of stochastic inversion which allows the input of a
priori information to the solver in terms of regularization variances. The
reconstruction is carried out in two stages. In the first inversion, constant
regularization variances are used within a wide altitude range. The results are
used in determining the approximate altitude range of the airglow structures.
Then, in the second inversion, constant non-zero regularization variances are
used inside this region and zero variances outside it. With this method reliable
reconstructions of the models are obtained. The number of cameras as well as
their separations are varied in order to find out the limitations of the method.
Key words. Tomography · Airglow · Mesopause ·
Gravity waves
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