Optical Turbulence Forecasting for Directed Energy and Laser Communication Systems

We have designed a state-of-the-art optical turbulence forecasting system for free-space optical (FSO) laser communication and directed energy laser weapons systems applications. Our initial emphasis has been on an improved atmospheric decision aid (ADA) for the Airborne Laser (ABL), but the methods can be equally applied to other laser-weapon systems, high-bandwidth laser-communication applications, and flight-level and high-altitude turbulence forecasts for military and commercial-aviation applications. Components of the system include: a)~more sophisticated gravity-wave and turbulence prediction methods and b)~improving the Air Force Weather Agency (AFWA) numerical weather prediction (NWP) model on which the ABL ADA is based. Our scientific approach for (a) inspired the development of hybrid deterministic/probabilistic methods that incorporate Bayesian Hierarchical Modeling (BHM) for forecasting turbulence and optical turbulence, including forecast uncertainty. Such methods integrate results from high- resolution direct numerical simulations and large-eddy simulations with observational data (e.g., rawinsonde, aircraft, radar, satellite, etc.) to deduce probability distributions for Cn2, path-integrated Rytov variance, etc. Our approach to (b) involves a much-improved upper boundary condition, adaptive-mesh refinement, and a novel subgrid-scale (SGS) modeling method that switches between a more conventional SGS scheme where the local spatial resolution is high and a BHM-based probabilistic method where the local resolution is coarse.