Objective: To develop a simulator of optical propagation based on a high-resolution numerical atmospheric simulator, to be used forthe long-term characterisation and the forecast of the signal scintillation and other propagation effects in the area around a ground terminal for Earth-Space optical communication system. Targeted Improvements: Breakthrough to achieve regional optical channel performance assessment; achieve high resolution channel prediction from remote sensing data. Description: Atmospheric turbulence in the earth boundary layer induces signal scintillation. This propagation effect is particularly relevant for optical links because it is highly localised, has a fast dynamic and coherence time. Atmospheric turbulence is caused by fast variations in time and space ofair temperature and water vapour, causing turbulent eddies that dissipate their energy in the atmosphere. Optical signal scintillation can be mitigated using adaptive optics coupled with now-casting algorithms (i.e. over few minutes) but it is quite difficult to characterise statistically turbulence with independent atmospheric remote sensing techniques and at the moment it cannot be forecasted for hours or days in advance. A high resolution atmospheric numerical model can resolve these patterns in time and space, in particular at optical frequencies where temperature variations are more relevant. The output of the atmospheric numerical model can be used as input to an EM optical propagation module to estimate the occurrence of signal scintillation and other atmospheric propagation effects. This system can then be used to: a) perform the analysis of the propagation conditions of a ground station over a long period (i.e. 1 year or more (providing site specific statistical distributions of optical propagation parameters for accurate system design and dimensioning. b) produce forecast of scintillation and other optical propagation parameters up from few hours to few days in the future to plan for use of techniques for mitigation of propagation effects (e.g. coding, adaptive optics, site or time diversity). The model can be validated by analysing data collected in previous campaigns both at optical and radio frequency (which is also affected by turbulence).This system is aims to complement ground propagation, remote sensing and meteorological measurements permitting their synergetic use. In addition, the data produced by this system can be used to train the ML algorithms for now-casting of optical propagation conditions and for the pre-processing of long-term experimental campaigns. Software shall be delivered under an ESA Software Community Licence, so that any individuals or entities within ESA Member States can access to it and can provide updateto the community of users.

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