The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Inverse Problems in Stellar Occultation

Viktoria Sofieva

Dissertation for the degree of Doctor of Philosophy to be presented with due permission of the Department of Engineering Physics and Mathematics for public examination and debate in Auditorium E at Helsinki University of Technology (Espoo, Finland) on the 22nd of April, 2005, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-7597-X)   [1315 KB]
Dissertation is also available in print (ISBN 951-697-610-7)

Abstract

Remote sensing plays a key role in monitoring the atmosphere, which becomes increasingly important for the Earth's changing environment. The stellar occultation technique is a novel method to monitor vertical distribution of ozone and other trace gases from the troposphere to the upper mesosphere. GOMOS (Global Ozone Monitoring by Occultation of Stars) flying on board the European Space Agency's ENVISAT satellite is the first operational stellar occultation instrument.

Satellite measurements are indirect, and therefore inversion methods play a key role in the retrieval of atmospheric parameters. This dissertation is dedicated to inversion methods for stellar occultation measurements and to the optimization of retrievals.

Optimization of retrievals by inclusion of a priori information about smoothness of atmospheric profiles is considered. Two methods are developed. One of them –"the target resolution method"– develops the classical Tikhonov regularization. The second method includes smoothness a priori information in the form of Bayesian optimal estimation. The methodology for creating a priori information about smoothness of atmospheric profiles is developed.

This dissertation considers optimal selection of measurements based on information theory, aiming at optimal design of future instruments, as well as at improved efficiency of the current data processing. Two optimization problems, both taking the information content of the measurements as a criterion, are defined and discussed. The selecting procedures were developed, compared with each other and existing methodologies and applied to selection of the most informative channels for GOMOS measurements in the UV-Visible wavelength range.

The dissertation presents a feasibility study for retrieval of temperature and density profiles from pointing measurements by stellar occultation instruments. This study introduces extra geophysical parameters that can be obtained from GOMOS measurements.

The inversion methods developed are applied to GOMOS measurements. However, the methods are formulated in a general form that allows their application beyond the GOMOS mission.

This thesis consists of an overview and of the following 6 publications:

  1. V. F. Sofieva, J. Tamminen, H. Haario, E. Kyrölä and M. Lehtinen. 2004. Ozone profile smoothness as a priori information in the inversion of limb measurements. Annales Geophysicae, Vol. 22, No. 10, pp. 3411-3420.
  2. V. F. Sofieva, E. Kyrö and E. Kyrölä. 2004. Smoothness of ozone profiles: analysis of 11-years of ozone sonde measurements at Sodankylä. Annales Geophysicae, Vol. 22, No. 8, pp. 2723-2727.
  3. V. F. Sofieva and E. Kyrölä. 2003. Information approach to optimal selection of the spectral channels. Journal of Geophysical Research, 108 (D16), 4513, doi: 10.1029/2002JD002980.
  4. V. F. Sofieva and E. Kyrölä. 2004. Abel integral inversion in occultation measurements. In: G. Kirchengast, U. Foelshe and A. Steiner (editors), Occultations for Probing Atmosphere and Climate. Springer-Verlag, pp. 77-86.
  5. V. F. Sofieva, E. Kyrölä, J. Tamminen and M. Ferraguto. 2004. Atmospheric density, pressure and temperature profile reconstruction from refractive angle measurements in stellar occultation. In: G. Kirchengast, U. Foelshe and A. Steiner (editors), Occultations for Probing Atmosphere and Climate. Springer-Verlag, pp. 289-298.
  6. V. F. Sofieva, E. Kyrölä, M. Ferraguto and GOMOS CAL/VAL team. 2003. From pointing measurements in stellar occultation to atmospheric temperature, pressure and density profiling: simulations and first GOMOS results. In: Proceedings of the 2003 IEEE International Geoscience and Remote Sensing Symposium (IGARSS 2003). ISBN 0-7803-7930-6.

Keywords: inverse problems, atmospheric remote sensing, occultation of stars, GOMOS, ozone, information theory

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© 2005 Helsinki University of Technology

Last update 2011-05-26