Sky coverage results are presented for several natural guide star (NGS) and laser guide star (LGS) adaptive optics (AO) configurations using scenario, telescope, and AO design parameters derived from the Gemini-North 8 m telescope. "Sky coverage" is defined as that fraction of the sky over which the AO system provides a useful level of performance, in this case a high Strehl ratio in the J, H, or K band. Some of the factors considered in this study include optimization of the AO wavefront reconstruction algorithm and control bandwidth, the effect of windshake-induced tip/tilt jitter, and the conjugation of the AO system's deformable mirror (DM) and wavefront sensor (WFS) to the dominant seeing layer at the Gemini-North site. The degree of compensation of the tip/tilt guide star image by the higher order adaptive optics is also considered. LGS AO using a single beacon in the mesospheric sodium layer typically improves sky coverage by about an order of magnitude relative to NGS AO, principally because a very dim natural guide star is sufficient for tip/tilt sensing when its image is sharpened by LGS higher order compensation. The values assumed for windshake, seeing, zenith angle, and the conjugate range of the DM and WFS also have a highly significant effect upon the estimated sky coverage for both the NGS and the LGS AO systems. The first three of these factors will need to be considered by scheduling algorithms for queue-based observing.1. Sky coverage defined in terms of high Strehl ratios in J, H, and K bands. 2. Atmospheric models corresponding to the Gemini-North site.

Superresolution by data inversion is the extrapolation of measured Fourier data to regions outside the measurement bandwidth using post processing techniques. Here we characterize superresolution by data inversion for objects with finite support using the twin concepts of primary and secondary superresolution, where primary superresolution is the essentially unbiased portion of the superresolved spectra and secondary superresolution is the remainder. We show that this partition of superresolution into primary and secondary components can be used to explain why some researchers believe that meaningful superresolution is achievable with realistic signal-to-noise ratios, and other researchers do not.

The end-to-end performance achieved by an adaptive optical (AO) imaging system is determined by a combination of the residual time-varying phase distortions associated with atmospheric turbulence and the quasi-static unsensed and uncorrectable aberrations in the optical system itself. Although the effects of these two errors on the time-averaged Strehl ratio and the time-averaged optical transfer function (OTF) of the AO system are not formally separable, such an approximation is found to be accurate to within a few percent for a range of representative residual wave-front errors. In these calculations, we combined static optical system aberrations and time-varying residual phase distortion characteristics of a deformable mirror fitting error, wave-front sensor noise, and anisoplanatism. The static aberrations consist of focus errors of varying magnitudes as well as a combination of unsensed and uncorrectable mirror figure errors derived from modeling by the Gemini 8-Meter Telescopes Project. The overall Strehl ratios and OTF's that are due to the combined effect of these error sources are well approximated as products of separate factors for the static and time-varying aberrations, as long as the overall Strehl ratio that is due to both errors is greater than approximately 0.1. For lower Strehl ratios, the products provide lower bounds on the actual values of the Strehl ratio and the OTF. The speckle transfer function is also well approximated by a product of two functions, but only where AO compensation is sufficiently good that speckle imaging techniques are usually not required.

Adaptive optics image data acquired on large telescopes nearly always need postdetection processing. We have designed a new algorithm for fast phase estimation from the bispectrum. Our innovative "part-bispectrum" approach to phase estimation addresses the large, instantaneous memory required to form the bispectrum of data measured on large-format detectors. The part-bispectrum approach has been further extended to run on parallel machines, hence the name "parallel part-bispectrum" algorithm. We describe the concept, design, and optimization of the algorithm and provide execution times for a variety of scenarios.

We present preliminary results from a comparison of image estimation and recovery algorithms developed for use with advanced telescope instrumentation and adaptive optics systems. Our study will quantitatively compare the potential of these techniques to boost the resolution of imagery obtained with undersampled or low-bandwidth adaptive optics; example applications are optical observations with JR-optimized AO, AO observations in severe turbulence, and AO observations with dim guidestars. We will compare the algorithms in terms of morphological and relative radiometric accuracy as well as computational efficiency. Here, we present qualitative comments on image results for two levels each of seeing, object brightness, and AO compensation/wavefront sensing.