Wave front control techniques for imaging space objects at large zenith angles

The problem of mitigating atmospheric turbulence-induced distortions from imagery measured by astronomical and space surveillance telescopes operating at high zenith angles is addressed here. Most previous research in this problem has emphasized operation at relatively small zenith angles, where turbulence effects are less severe, and effects arising from relatively weak phase distortions dominate the measurements. As the zenith angle increases the propagation path through the atmosphere gets progressively longer, with the result that the wave front arriving at the telescope is corrupted by both phase and amplitude fluctuations. This poses a problem for conventional adaptive optics systems because the assumptions implicit to their design and construction are violated. Our goal is to examine and compare the performance of two approaches to deformable mirror control a conventional recursive technique, and the slope discrepancy technique. We created a closed loop adaptive optics imaging simulation of an AEOS-like adaptive optics system imaging a star at zenith angles in the range 0 70 degrees using both deformable mirror control paradigms, and compare performance. Our results show that the slope discrepancy wave front reconstructor provides significantly better performance at all zenith angles, but this performance advantage is particularly strong at high zenith angles.