27 July 2010 Online wind estimation and prediction for a two-layer frozen flow atmosphere
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Abstract
We present a method for online estimation and prediction of wavefront distortions caused by two independent layers of frozen flow turbulence. The key to this algorithm is a fast, gradient-based estimator that uses optical flow techniques to extract the bulk velocity vectors of the two wind layers from three consecutive measurements of their combined wavefront. Once these velocity vectors are known, the phase aberrations resulting from the two-layer atmosphere can be predicted at any future time using a linear combination of shifted wavefronts. This allows calculation of a deformable mirror correction that compensates for the time delay errors in the control loop. Predictive control will be especially beneficial for visible light and high-contrast astronomical adaptive optics as well as for any adaptive optics system whose performance suffers due to time delay errors. A multilayer approach to predictive control is necessary since most observing sites have multi-layer atmospheres. The spatial domain method that we present is attractive because it uses all spatial frequency components of the wavefront simultaneously to find a global wind model. Its ability to update the wind velocity estimate at each control cycle makes it sensitive to changes in the wind on the order of tens of milliseconds. Our simulations show a potential Strehl increase from 0.45 to 0.65 for visible-light adaptive optics in low-noise, moderate-wind conditions with two frozen-flow wind layers and a strong static layer.
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Luke C. Johnson, Luke C. Johnson, Donald T. Gavel, Donald T. Gavel, Donald M. Wiberg, Donald M. Wiberg, } "Online wind estimation and prediction for a two-layer frozen flow atmosphere", Proc. SPIE 7736, Adaptive Optics Systems II, 77362R (27 July 2010); doi: 10.1117/12.857704; https://doi.org/10.1117/12.857704
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