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Solar Physics

, Volume 214, Issue 1, pp 89–105 | Cite as

A full-disk image standardisation of the synoptic solar observations at the Meudon Observatory

  • V.V. Zharkova
  • S.S. Ipson
  • S.I. Zharkov
  • A. Benkhalil
  • J. Aboudarham
  • R.D. Bentley
Article

Abstract

Robust techniques are developed to put the Hα and Ca K line full-disk images taken at the Meudon Observatory into a standardised form of a `virtual solar image'. The techniques include limb fitting, removal of geometrical distortion, centre position and size standardisation and intensity normalisation. The limb fitting starts with an initial estimate of the solar centre using raw 12-bit image data and then applies a Canny edge-detection routine. Candidate edge points for the limb are selected using a histogram based method and the chosen points fitted to a quadratic function by minimising the algebraic distance using SVD. The five parameters of the ellipse fitting the limb are extracted from the quadratic function. These parameters are used to define an affine transformation that transforms the image shape into a circle. Transformed images are generated using the nearest neighbour, bilinear or bicubic interpolation. Intensity renormalisation is also required because of a limb darkening and other non-radial intensity variations. It is achieved by fitting a background function in polar coordinates to a set of sample points having the median intensities and by standardising the average brightness. Representative examples of intermediate and final processed results are presented in addition to the algorithms developed. The research was done for the European Grid of Solar Observations (EGSO) project.

Keywords

Geometrical Distortion Solar Image Solar Observation Choose Point Bicubic Interpolation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Kluwer Academic Publishers 2003

Authors and Affiliations

  • V.V. Zharkova
    • 1
  • S.S. Ipson
    • 1
  • S.I. Zharkov
    • 1
  • A. Benkhalil
    • 1
  • J. Aboudarham
    • 2
  • R.D. Bentley
    • 3
  1. 1.Department of CyberneticsBradford UniversityBradfordU.K
  2. 2.LESIA, The Paris-Meudon ObservatoryMeudon Principal CedexFrance
  3. 3.MSSL, University College LondonHombury St. Mary, Dorking, SurreyU.K

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