AAS 200th meeting, Albuquerque, NM, June 2002
Session 55. Solar Data Analysis and Calibration
Display, Wednesday, June 5, 2002, 10:00am-7:00pm, SW Exhibit Hall

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[55.01] A Method for Measuring the Image Distortion in the GONG Solar Telescopes

J.J. Sudol, J.W. Harvey, C.G. Toner (Global Oscillation Network Group, National Solar Observatory)

The accuracy of the results of local helioseismology studies is limited in part by image distortion. The Global Oscillation Network Group (GONG) operates six identical solar telescopes worldwide which continuously obtain full disk intensity images, velocity images, and magnetograms at one minute intervals at a resolution of 2.5 arcseconds per pixel. The theoretical distortion in the images obtained with these telescopes is 0.004 pixel at the solar limb. The true distortion, though, is unknown and might be higher than the theoretical distortion depending on the quality of the alignment of the optics and the extent to which the optical components deviate from their design specifications. Observations of sources other than the Sun are not possible with the GONG solar telescopes, so traditional methods for measuring distortion cannot be used.

We propose a method for measuring the distortion in the images obtained with the GONG solar telescopes to 0.01 pixel, and we present the results of several simulations of this method. We intend to construct an optical system to project sunlight onto a pinhole plate that lies at the focus of a lens in front of the entrance window of the solar telescope. An optical wedge between the lens and the entrance window will allow us to translate the image of the pinhole plate to sample the distortion across the image plane. Given a sequence of images of the pinhole plate, we will solve simultaneously for the relative positions of the pinholes on the plate and the distortion.

The author(s) of this abstract have provided an email address for comments about the abstract: jsudol@noao.edu

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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.