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 fu ll-disk solar intensity images that is insensitive to changes in the o bservational point spread function. The method exploits the zero-cross ing properties of the Fourier transform of an observed image to recove r the image's true dimensions and to reconstruct an azimuthally averag ed estimate for the point spread function. Simulations show that the u ndistorted image dimensions can be reproduced to better than 0.01 of a resolution element, and that the point spread function can be recover ed to within 5% at low spatial frequencies and 15% at high spatial fre quencies. Preliminary tests with real data confirm the results from th e simulations and show the method to be robust.