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Open Access

Technique for Automated Recognition of Sunspots on Full-Disk Solar Images

EURASIP Journal on Advances in Signal Processing20052005:318462

Received: 31 May 2004

Published: 14 September 2005


A new robust technique is presented for automated identification of sunspots on full-disk white-light (WL) solar images obtained from SOHO/MDI instrument and Ca II K1 line images from the Meudon Observatory. Edge-detection methods are applied to find sunspot candidates followed by local thresholding using statistical properties of the region around sunspots. Possible initial oversegmentation of images is remedied with a median filter. The features are smoothed by using morphological closing operations and filled by applying watershed, followed by dilation operator to define regions of interest containing sunspots. A number of physical and geometrical parameters of detected sunspot features are extracted and stored in a relational database along with umbra-penumbra information in the form of pixel run-length data within a bounding rectangle. The detection results reveal very good agreement with the manual synoptic maps and a very high correlation with those produced manually by NOAA Observatory, USA.

Keywords and phrases

digital solar imagesunspotslocal thresholdedge-detectionmorphological operatorssunspot area time series

Authors’ Affiliations

Department of Cybernetics, University of Bradford, West Yorkshire, UK


© S. Zharkov et al. 2005

This article is published under license to BioMed Central Ltd. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.