Filtering techniques to enhance optical turbulence forecast performances at short time-scales

Abstract

The efficiency of the management of top-class ground-based astronomical facilities supported by adaptive optics (AO) relies on our ability to forecast the optical turbulence (OT) and a set of relevant atmospheric parameters. Indeed, in spite of the fact that the AO is able to achieve, at present, excellent levels of wavefront corrections (a Strehl ratio up to 90 per cent in H band), its performances strongly depend on the atmospheric conditions. Knowing in advance the atmospheric turbulence conditions allows an optimization of the AO use. It has already been proven that it is possible to provide reliable forecasts of the OT (C2 N profiles and integrated astroclimatic parameters such as seeing, isoplanatic angle, wavefront coherence time, etc.) for the next night. In this paper, we prove that it is possible to improve the forecast performances on shorter time-scales (order of 1 or 2 h) with consistent gains (order of 2–8) employing filtering techniques that make use of real-time measurements. This has permitted us to achieve forecasts accuracies never obtained before and reach a fundamental milestone for the astronomical applications. The time-scale of 1 or 2 h is the most critical one for an efficient management of the ground-based telescopes supported by AO. We implemented this method in the operational forecast system of the Large Binocular Telescope (LBT), named Advanced LBT Turbulence and Atmosphere (ALTA) Center that is, at our knowledge, the first operational system providing forecasts of turbulence and atmospheric parameters at short time-scales to support science operations.