Physics – Optics
Scientific paper
Nov 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010phdt........97j&link_type=abstract
ProQuest Dissertations And Theses; Thesis (Ph.D.)--University of California, Santa Cruz, 2010.; Publication Number: AAT 3442805;
Physics
Optics
Scientific paper
I present and analyze a method for predictive wavefront control of astronomical adaptive optics that has the potential to significantly improve adaptive optics system performance. This method adapts the Kalman filter framework, assuming a partially deterministic atmospheric model containing frozen-flow turbulence. Atmospheric parameters are determined online, during closed-loop operation, with methods that can be run in real-time on existing systems. Parameter estimation is done in the spatial domain so that it makes use of all wavefront spatial frequency modes simultaneously, leading to a quickly converging algorithm capable of tracking wind changes on millisecond timescales. I derive the fundamental limits of wind velocity estimation for one and two layers of frozen-flow wind. This detailed analysis, combined with an expression for wavefront error due to wind estimate variance, provides a measure of controller robustness not just for the specific control methods presented but also for any wind-predictive controller. It also allows for prediction of actual performance improvement from using a wind-predictive controller, a valuable tool for adaptive optics system design. I present two controllers. The first for a single-wind atmosphere consisting of windblown turbulence and quasi-static turbulence and the second for an atmosphere with two windblown layers. The second controller works well even on atmospheres with more than two windblown layers. I also show simulations using both artificial and on-sky wavefront data that indicate the parameter space in which predictive control is useful and demonstrate its potential to improve adaptive optics wavefront correction. I conclude that the presented methods for wind-predictive control of adaptive optics are feasible for real-time systems and have the potential to effect significant performance improvements. However, some care must be taken to properly account for atmospheric conditions and system error budgeting in order to gain the most benefit from predictive wavefront control.
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