Modelling of atmospheric optical turbulence has been of interest in astronomy for several decades, e.g. for site characterization and flexible scheduling. Nowadays, it is also considered for free-space optical communications, namely to conduct site selection and to design future optical communication systems. In this work, a general approach relying on numerical weather prediction simulations in order to perform optical turbulence prediction is presented. The approach makes use of the Weather Research and Forecasting model and raises several challenges. The latter, such as the choice of the C2n models or the required temporal and spatial resolutions, are first discussed with regards to the literature. Then, optical turbulence prediction is conducted for the site of Redu, Belgium, illustrating the different challenges. These predictions are also compared with seeing measurements from a differential image motion monitor. The presented approach offers realistic seeing values that, however, do not follow rapid variations of the measured seeing. Origins of the discrepancies between measurements and predictions are to be found in the modelling of the boundary layer and motivate the use of a C2n model relying on the turbulent kinetic energy. Further simulations and measurement campaigns at other optical communication sites are encouraged in order to refine some model parameters and compare statistically the prediction results. Additional presentation content can be accessed on the supplemental content page.
SALTO is a Belgian project aiming to build a complete 1 m telescope demonstrator including a single-conjugated adaptive optics (AO) system together with a Rayleigh laser guide star system. The underlying objective of SALTO consists in developing the Belgian expertise regarding AO systems for medium size telescopes (i.e. diameter from 1 to 4m), for application in astronomy, optical communication or detection of low-Earth orbit objects. The project approach is to base the design on COTS components, in order to reduce complexity, and to favor both robustness and automation of the system over performance. The SALTO demonstrator will be located at Redu Space Services in the Belgian countryside. Therefore the major challenge of the project will be to deal with poor seeing, far worst than astronomical standards, while preserving robust and reasonable correction in the red-visible and near-infrared wavelength range. Here, we present our system baseline, the expected performance, and the preliminary design of the AO system. We conclude with the current prospects for the project.
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