Effects of wind-driven telescope vibrations on measurements of turbulent angle-of-arrival fluctuations

Abstract

Turbulence in the atmospheric refractive-index field causes optical angle-of-arrival (AOA) fluctuations that can be used for atmospheric remote sensing of various parameters, including wind velocities and the optical refractive-index turbulence structure parameter, C(n)2. If AOA measurements are contaminated by wind-induced telescope vibrations, the underlying retrieval algorithms may fail. In order to study the effects of wind-driven telescope vibrations on optical-turbulence measurements, we conducted a field experiment in which we exposed two small telescopes deliberately to the wind. We measured AOA fluctuations of visible light propagating along a horizontal, 174 m long path 1.7 m above flat terrain, and we used fast-response ultrasonic anemometers to measure the wind velocity at multiple locations along the path. We found (1) that the AOA turbulence spectra were contaminated by multiple resonance peaks, (2) that the resonance frequencies were independent of the wind speed, and (3) that the AOA variance associated with the dominating vibration mode was proportional to the fourth power of the wind speed.

Measurement Science of the Intermittent Atmospheric Boundary Layer

“…• The observed AOA rms value σ AOA resulting from a wind-driven telescope resonance appears to be consistent with the scaling law (Tichkule and Muschinski, 2013)…”

“…As an alternative to our heavy, 36-cm telescopes ($7,000 a piece), we studied the performance of light-weight, inexpensive, 11-cm telescopes ($200 a piece). In order to understand their vulnerability to wind-driven vibrations, we exposed them deliberately to the wind (Tichkule and Muschinski, 2013).…”

Compensation Techniques Aimed at Mitigating Vibrations in Optical Ground-Based Telescopes: A Systematic Review

“…Tichkule and Muschinski studied the effects of wind-driven telescope vibrations on optical turbulence measurements. In particular, on optical angle-of-arrival (AOA) fluctuations [ 16 ].…”

“…These systems are essential to achieve much higher angular resolutions and thereby improve the quality of the images [ 23 ]. AO systems have proven to be robust in compensating for the effect of wavefront distortion due to atmospheric turbulence by using deformable mirrors [ 24 , 25 , 26 , 27 ] as well as for mitigating vibrations due to the telescope structure [ 16 , 28 , 29 ]. Even so, there is a level of disturbance energy that still remains and needs to be minimized, since disturbances affect the correction of the wavefronts.…”