Optical turbulence vertical distribution with standard and high resolution at Mt Graham

Abstract

A characterization of the optical turbulence vertical distribution (C2N profiles) and all the main integrated astroclimatic parameters derived from the C2N and the wind speed profiles above the site of the Large Binocular Telescope (LBT) (Mt Graham, Arizona, USA) is presented. The statistics include measurements related to 43 nights done with a Generalized SCIDAR (GS) used in standard configuration with a vertical resolution ΔH∼ 1 km on the whole 20 km and with the new technique (High Vertical Resolution GS) in the first kilometre. The latter achieves a resolution ΔH∼ 20–30 m in this region of the atmosphere. Measurements done in different periods of the year permit us to provide a seasonal variation analysis of the C2N. A discretized distribution of C2N, useful for the Ground Layer Adaptive Optics (GLAO) simulations, is provided and a specific analysis for the LBT Laser Guide Star system ARGOS (running in GLAO configuration) case is done including the calculation of the ‘grey zones’ for J, H and K bands. Mt Graham is confirmed to be an excellent site with median values of the seeing without dome contribution ɛ= 0.72 arcsec, the isoplanatic angle θ0= 2.5 arcsec and the wavefront coherence time τ0= 4.8 ms. We find that the OT vertical distribution decreases in a much sharper way than what has been believed so far in the proximity of the ground above astronomical sites. We find that 50 per cent of the whole turbulence develops in the first 80 ± 15 m from the ground. We finally prove that the error in the normalization of the scintillation that has been recently demonstrated in the principle of the GS technique affects these measurements by an absolutely negligible quantity (0.04 arcsec).

Lunar scintillometer to validate GLAO turbulence distribution measurements

“…This result is consistent with turbulence distributions obtained by Masciadri et al [6] on nearby Mount Graham, Arizona. Preliminary results using the same high vertical resolution generalized-SCIDAR approach, proposed by Egner et al [7], showed a similar concentration of turbulence near the ground.…”

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

“… We consider it extremely important to take into consideration the atmospheric data of the different sites in order to improve the adaptive optics systems by using the different atmospheric turbulence profiles. In this way, the systems would be calibrated according to the sky in which they operate [ 70 , 71 , 72 , 73 , 74 , 75 , 76 ]. Control applications also should be developed taking into account the particularities of each telescope and environment where it is currently operating.…”

SHARK (System for coronagraphy with High order Adaptive optics from R to K band): a proposal for the LBT 2nd generation instrumentation

“…Also on the seeing point of view, Mount Graham has shown a behavior remarkably good (see [26] e [20]), with an average estimated seeing of about 1" achieved during the commissioning of FLAO and, furthermore, with several nights in which the seeing has been lower than 0.8" and sometimes as good as 0.3" in V Band.…”