Abstract
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.
Highlights
Sunspot identification and characterisation including location, lifetime, contrast, and so forth, are required for a quantitative study of the solar cycle
Sunspot studies play an essential part in the modelling of the total solar irradiance during the solar cycle
The algorithm performs well when trained appropriately, the training process itself can be rather difficult to arrange on images with different background variations corresponding to varying observing conditions. Another approach to sunspot area measurements utilising edge-detection and boundary gradient intensity was suggested for high-resolution observations of individual sunspot groups, and/or non-full-disk segments by Gyori [14]
Summary
Sunspot identification and characterisation including location, lifetime, contrast, and so forth, are required for a quantitative study of the solar cycle. The algorithm performs well when trained appropriately, the training process itself can be rather difficult to arrange on images with different background variations corresponding to varying observing conditions Another approach to sunspot area measurements utilising edge-detection and boundary gradient intensity was suggested for high-resolution observations of individual sunspot groups, and/or non-full-disk segments by Gyori [14]. The techniques presented are used for the detection of sunspots on white-light and Ca II K1 line full-disk images, extracting sunspot sizes, locations, umbra and penumbra areas and intensities with high accuracy restricted only by pixel resolution.
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