IMAGE-QUALITY METRICS FOR CHARACTERIZING ADAPTIVE OPTICS SYSTEM PERFORMANCE

Adaptive optics system (AOS) performance is a function of the system d esign, seeing conditions, and light level of the wave-front beacon. It is desirable to optimize the controllable parameters in an AOS to max imize some measure of performance. For this optimization to be useful, it is necessary that a set of image-quality metrics be developed that vary monotonically with the AOS performance under a wide variety of i maging environments. Accordingly, as conditions change, one can be con fident that the computed metrics dictate appropriate system settings t hat will optimize performance. Three such candidate metrics are presen ted. The first is the Strehl ratio; the second is a novel metric that modifies the Strehl ratio by integration of the modulus of the average system optical transfer function to a noise-effective cutoff frequenc y at which some specified image spectrum signal-to-noise ratio level i s attained; and the third is simply the cutoff frequency just mentione d. It is shown that all three metrics are correlated with the rms erro r (RMSE) between the measured image and the associated diffraction-lim ited image. Of these, the Strehl ratio and the modified Strehl ratio e xhibit consistently high correlations with the RMSE across a broad ran ge of conditions and system settings. Furthermore, under conditions th at yield a constant average system optical transfer function, the modi fied Strehl ratio can still be used to delineate image quality, wherea s the Strehl ratio cannot.