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Full-disk spectroheliograms have been taken in Coimbra on a daily basis since1926 in the Ca II K-line (K1 and K3). Later, in 1989, with the upgrade of theequipment it was possible to start the observations in the H-alpha line. Thespectroheliograms of Coimbra constitutes a huge dataset of solar images, whichrequires an efficient automatic tool to detect and analyse solar activityfeatures. This work presents a mathematical morphology approach applied to theCaII K3 series. The objective is to create a tool based on the segmentation bywatershed transform combined with other morphological operators to detectautomatically and analyse chromospheric plages during the solar cycle 24. Thetool is validated by comparing its results for cycle 23 with those presented byDorotovic et al. (2007, 2010). The results obtained are in very good agreementwith those, including on images obtained in non-ideal meteorological conditions(eg. some clouds in sky). The results were also qualitatively compared with theresults obtained through the application of ASSA model to SDO HMI magnetograms.

Software tool for automatic detection of solar plages in the Coimbra Observatory spectroheliograms