Kavli Affiliate: Bruce Macintosh
| First 5 Authors: Zhenxi Du, Saavidra Perera, Daniel Levinstein, Quinn Konopacky, Alex Madurowicz
| Summary:
The Earth’s atmosphere is comprised of turbulent layers that result in
speckled and blurry images from ground-based visible and infrared observations.
Adaptive Optics (AO) systems are employed to measure the perturbed wavefront
with a wavefront sensor (WFS) and correct for these distortions with a
deformable mirror. Therefore, understanding and characterising the atmosphere
is crucial for the design and functionality of AO systems. One parameter for
characterizing the atmosphere is the atmospheric coherence time, which is a
function of the effective wind velocity of the atmosphere. This parameter
dictates how fast the AO system needs to correct for the atmosphere. If not
fast enough, phenomena such as the wind butterfly effect can occur, hindering
high-contrast coronographic imaging. This effect is a result of fast, strong,
high-altitude turbulent layers. This paper presents two methods for estimating
the effective wind velocity, using pseudo-open loop WFS slopes. The first
method uses a spatial-temporal covariance map and the second uses the power
spectral density of the defocus term. We show both simulated results and
preliminary results from the Gemini Planet Imager AO telemetry.
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