Computer Science
Scientific paper
Dec 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993rtpf.conf...89l&link_type=abstract
Real time and post facto solar image correction, proc. 13th NSO/Sac Peak Summer Workshop, NSO/SP summer workshop series No. 13,
Computer Science
1
Scientific paper
We have implemented a least-squares linearization technique for recovering phase information from simultaneously recorded focused and defocused solar images. The inversion is made from small subfields, in order to deal with anisoplanatic image formation, such as occuring through the earth's atmosphere. Simulations show that the method can recover wavefronts of approximately 1/4 wave rms and that noise levels corresponding to 8-bit images allow better reconstruction of the images than of the derived wavefronts. We find that cross-correlation techniques cannot be used to align the focused and defocused images because of cross-talk with coma and similar asymmetric aberrations. Therefore we simultaneously determine alignment and aberration parameters. We have applied the method to 8-bit solar granulation images obtained with the Swedish Vacuum Solar Telescope in La Palma using subfields of 3".1 x 3".1. The least-squares fits indicate wavefronts of approximately 0.12-0.16 waves rms. Derived alignment parameters from different subfields and different images are consistent, indicating that the wavefront is well determined by the data. Wavefronts derived from different sub fields of a single image in general show similar aberrations whereas derived wavefronts from different images only show occasional similarities, indicating a significant wavefront aberration from the lower atmosphere. The reconstructed granulation images show enhanced fine structure and an increase of the rms contrast by ~2% as compared to the observed focused image, but the rms contrasts of consequtive images indicate small errors in the derived rms wavefronts.
Löfdahl Mats G.
Scharmer Goran B.
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