<title>A Statistical Method For Post-Detection Compensation For Atmospheric Distortions Of Images Of Faint Scenes</title>

Abstract

A new method for post-detection compensation of atmospheric distortions of images of faint scenes has been outlined and initially tested. A sequence of short exposure (0.01 to 0.1 sec) visible light images is processed in terms of the statistics of the Fourier transform amplitudes. A "master image" is derived that is iteratively compared with each image (in Fourier space) so as to align the set of images on the basis of features in the scene. Aperture synthesis can be used to decrease aperture redundancy since the alignment uses only Fourier amplitudes that are prominent in the joint set of master image and the raw image sequence. The master image has an effective point spread function (PSF) comparable to the best PSF in the sequence but the phases are strongly quieted by the statistics of large numbers if 30 or more images are spread over a time interval of 15 or more sec. Thus spatial frequencies in excess of 1 cycle per arcsec may yield reliable photometry after correction for contrast loss and telescope aberrations. The degree of enhancement may be optimized, based on a separation of signal and noise in the data so that noise may be estimated. At faint levels quantum noise is severe. Since that noise is correlated with signal, the noise spectrum is not white but falls with increasing spatial frequency.