ACCURATE MEASUREMENT OF THE GEOMETRY FOR A FULL-DISK SOLAR IMAGE AND ESTIMATION OF THE OBSERVATIONAL POINT-SPREAD FUNCTION

We present a new method for accurately determining the geometry for full-disk solar intensity images that is insensitive to changes in the observational point spread function. The method exploits the zero-crossing properties of the Fourier transform of an observed image to recover the image's true dimensions and to reconstruct an azimuthally averaged estimate for the point spread function. Simulations show that the undistorted image dimensions can be reproduced to better than 0.01 of a resolution element, and that the point spread function can be recovered to within 5% at low spatial frequencies and 15% at high spatial frequencies. Preliminary tests with real data confirm the results from the simulations and show the method to be robust.