Mees White Light Telescope

Quicklook Active Region Extract Movies

A set of MWLT images are processed and the sunspot regions extracted to form a mosaic movie. The relative evolution of the largest sunspot regions each day can be compared.

Automatic active region finding

The MWLT_MOVIE procedure automatically finds up to 6 active regions using only continuum images of the solar photosphere. The algorithm is as follows:

• 1) Subtract limb-darkening
• 2) Compute min, max images over window (5 pxl = 12.5 arcsec)
• 3) Compute Std. dev. of (min - max)
• 4) Find pixels < 3 Std. dev. below median of (min - max)
• 5) Sort on (min - max)

• 6) Take first marked pixel
• 7) Find all marked pixels within a limited FOV
• 8) Location is median of those
• 9) Drop marked pixels within FOV from list, loop to (6)

This works to find either sunspot regions or facular regions. Quite small pores are detectable, and most normal regions are well centered in the extracted FOV. In some cases, odd behavior occurs, and the following mprovements to this basic scheme are now options to the procedure:

• 1) Step 8 is used to center on a bipolar region, rather than the darkest spot. For large regions, an iteration between (7) and (8) slightly improves the situation. One problem is that separate but nearby regions can get mixed together; that is why the FOV is limited in (7).
• 2) Once the regions are found, it is often the case that the largest or most complex region is not the first. Keeping the number of marked pixels found at (7) helps decide which is the dominant region.
• 3) A further improvement is to factor in foreshortening, which increases the weight for large regions near the limb.

Last modified: Tue Sep 18 03:42:54 HST 2001