Atmospheric turbulence characterization with the Keck adaptive optics systems. I. Open-loop data

Area of Science:

• Astronomy and Astrophysics
• Optical Engineering

Background:

• Adaptive optics (AO) systems are crucial for mitigating atmospheric turbulence effects in astronomical observations.
• Accurate characterization of atmospheric turbulence is essential for optimizing AO system performance.

Purpose of the Study:

• To investigate and compare methods for characterizing atmospheric turbulence using AO systems at the W. M. Keck Observatory.
• To address challenges in separating instrumental and atmospheric effects and in device calibration.

Main Methods:

• Analysis of differential image motion structure functions.
• Zernike decomposition of the wave-front phase.
• Comparison with long-exposure image results.

Main Results:

• Both differential image motion and Zernike decomposition methods yield atmospheric coherence length (r0) values in excellent agreement with long-exposure data.
• Wave-front sensor calibration is identified as a primary source of error.
• Determined outer scale (L0) values are consistent across methods and with typical values at other observatories (tens of meters).

Conclusions:

• The investigated methods are reliable for characterizing atmospheric turbulence with AO systems.
• Accurate calibration of wave-front sensors is critical for precise turbulence measurements.
• The findings contribute to a better understanding of atmospheric parameters affecting astronomical observations.