RESTORATION OF LONG-EXPOSURE FULL-DISK SOLAR INTENSITY IMAGES

We describe an algorithm for restoring full-disk solar intensity image s blurred by a smooth, quasistationary point-spread function (PSF). Fo r Earth-based observations, this type of data can be obtained by using exposure times that are much longer than the redistribution time of t he atmosphere. Using simulated data for a wide range of observing cond itions, we show that the algorithm restores data in such a way that th e RMS difference between an original, unblurred image and the restored image is typically less than 1.0%. Thus, we substantially improve the photometric precision. The simulations also show that under ''reasona ble'' seeing conditions (less than or similar to 4 ''), exposure times of 5-10 s are adequate to produce smooth calibratable PSFs if the obs erving instrument uses a centroid-shifting tip/tilt wavefront correcti on. The algorithm determines the PSF for each observation directly fro m the recorded image and does not require separate measurements of poi nt sources.