IMAGE QUALITY, TIP-TILT CORRECTION, AND SHIFT-AND-ADD INFRARED IMAGING

The image quality obtainable with shift-and-add (SAA) imaging for the recovery of diffraction-limited information is quantitatively investigated using data simulating an 8-m aperture at a site with near-infrared seeing conditions as found on Mauna Kea. This is compared to the image quality obtainable from image centroiding and wavefront tip-tilt correction. For good seeing conditions, image centroiding and SAA, which tracks the image peak, show similar performance containing approximately 30% of the image power in a diffraction-limited component. However, as the seeing degrades, SAA consistently yields improved resolution maintaining significantly greater diffraction-limited information. This enhances the detection threshold by approximately 2 magnitudes over the seeing-limited case for the seeing range studied. By comparison the gain due to image centroiding decreases to < 1 magnitude at the same poor seeing limit.