Automatic Sunspots Detection on Full-Disk Solar Images using Mathematical Morphology
Sunspots are solar features located in active regions of the Sun, whose number is an indicator of the Sun’s magnetic activity. Therefore accurate detection and classification of sunspots are fundamental for the elaboration of solar activity indices such as the Wolf number. However, irregularities in the shape of the sunspots and their variable intensity and contrast with the surroundings, make their automated detection from digital images difficult. Here, we present a morphological tool that has allowed us to construct a simple and automatic procedure to treat digital photographs obtained from a solar telescope, and to extract the main features of sunspots. Comparing the solar indices computed with our algorithm against those obtained with the previous method exhibit an obvious improvement. A favorable comparison of the Wolf sunspot number time series obtained with our methodology and from other reference observatories is also presented. Finally, we compare our sunspot and group detection to that of other observatories.
KeywordsSunspots Automatic detection Mathematical morphology
Unable to display preview. Download preview PDF.
- Cordeiro, M.: 2001, Algorithmic Patterns for Morphological Image Processing, Prentice-Hall, Englewood Cliffs. Google Scholar
- Dougherty, E.R.: 1992, An Introduction to Morphological Image Processing, SPIE Optical Engineering Press. Google Scholar
- González, R.C., Woods, R.E.: 2002, Digital Image Processing, Prentice-Hall, Englewood Cliffs. Google Scholar
- Green, R.M.: 1985, Spherical Astronomy, Cambridge University Press, Cambridge. Google Scholar
- Hargreaves, J.K.: 1992, The Solar-Terrestrial Environment, University Press. Google Scholar
- Lanzerotti, L.J.: 2001, Space weather effects on communications. In: Daglis, I.A. (ed.) Space Storms and Space Weather Hazards, Kluwer, Dordrecht, 313 – 334. Google Scholar
- Neckel, H.: 1994, Solar limb darkening 1986 – 1990, Hamburger Sternwarte, Germany. Google Scholar
- Waldmeier, M.: 1961, The Sunspot-Activity in the Years 1610 – 1960, Schultheiss Publisher, Zürich. Google Scholar