Flat Fielding and Image Alignments for AIA/SDO Data Images

Details Flat Fielding and Image Alignments for AIA/SDO Data Images Flat Fielding and Image Alignments for AIA/SDO Data Images

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsh23c1872s&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SH23C-1872

Astronomy and Astrophysics

Astrophysics

[7594] Solar Physics, Astrophysics, And Astronomy / Instruments And Techniques

Scientific paper

The Atmospheric Imaging Assembly (AIA) on the NASA Solar Dynamics Observatory (SDO) takes 4096 by 4096 CCD images of the sun in 10 wavelengths utilizing 4 telescopes and each wavelength channel requires a flat field that is applied shortly after receipt of the data on the ground. Although some useful information about the CCD's was obtained pre-launch, most of the flat field computation must be done with solar images taken in orbit. Raw flat field images are collected as out of focus images at 14 offsets using PZT adjustments on each telescope and then each wavelength group is processed together using the Kuhn, Lin, and Loranz (1991) flat field algorithm. However, the PZT motions are restricted to about 14 arc sec limiting the measurement of large scale variations. Hence larger offsets are also used by adjusting the space craft pointing. All of these suffer from changes in the solar image between exposures (especially the larger offsets), low counts in some channels, and reflections in the UV channels. These make direct use of the flats unfeasible and instead we process them to compute 6 separable effects: 1) differences in the CCD quad gains and inner row/column effects, 2) a repeating pattern across the CCD from the manufacturing process (dubbed "tire tracks"), 3) a grid pattern in the extreme ultraviolet wavelengths from the back filter, 4) blemishes (some are translucent and some are treated as bad pixels), 5) large scale vignetting, and 6) all other variations. The last category includes all remaining flat field effects after the others are removed. This has not been done well for any of the wavelengths yet. These effects will be described and illustrated, as will the before and after images resulting from applying the processed flat fields. We also describe techniques for fitting the solar limb to accurately determine image centers and radii. This is not a trivial problem for the extreme ultraviolet images but is required to align images, determine relative plate scales, and monitor pointing variations related to thermal changes. All channels except the He II 304A can be now be routinely measured with an rms error of typically less than 0.2 arc sec. This allows us to easily see the radius variations during the 24 hour orbit for example. The computer code requires about 3 seconds (single threaded) for each measurement. This work was supported by NASA under the SDO/AIA contract NNG04EA00C.

Affiliated with

Also associated with

No associations

Rating

Flat Fielding and Image Alignments for AIA/SDO Data Images does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Flat Fielding and Image Alignments for AIA/SDO Data Images, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Flat Fielding and Image Alignments for AIA/SDO Data Images will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1508800