Implications for contrast as a result of the wind vector and non-stationary turbulence
conference paper
In an adaptive optics (AO) system, finite time delays contribute a relatively large amount to the overall wavefront error. The temporal error, due to the time delays, adds to the speckle halo which is visible in the science plane of a high contrast imaging (HCI) instrument. The halo limits the inner working angle, preventing HCI from probing regions where we expect Earth-like planets. Our research focuses on understanding the non-stationary behavior of atmospheric turbulence and its effects on the temporal error and the contrast. The wind vector greatly influences the turbulence-induced wavefront phase error. In the framework of the von Karman power spectral density (PSD) of wavefront phase, the wind speed changes the cut-off frequency as well as the gain of the spectrum. We aim to understand the behavior of the wind vector on sub-second timescales using data from the Thirty Meter Telescope site testing campaign at Mauna Kea. The nocturnal measurements we study are from 287 nights throughout the years of 2006-2008, taken at a height of 7 m with a maximum sampling rate of 60 Hz. We first compare the observational PSD to the Kaimal PSD. We then present an expression for the observational PSD, a fit to a more general PSD similar to the Kaimal PSD, to describe the wind speed located at Area E (northern plateau) on Mauna Kea. Using the fitted PSD, we construct a fractionally integrated ARMA model that can be used to create an artificial wind speed time series to be fed into phase screen simulations to generate realistic wind-varying phase screens. We examine how the contrast, achieved by the AO system, varies with the wind fluctuations.
Topics
TNO Identifier
842694
ISSN
0277786X
ISBN
9781510619593
Publisher
SPIE
Article nr.
107032C
Source title
Adaptive Optics Systems VI, Austin, TX, USA, 10-15 June 2018
Editor(s)
Schmidt, D.
Schreiber, L.
Close, L.M.
Schreiber, L.
Close, L.M.
Collation
15 p.
Files
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