Modeling microphysical influences on optical turbulence in complex areas

Summary

An earlier paper showed that there is a growing need for increasingly accurate and reliable numerical models to predict optical turbulence conditions, especially in complex (nonuniform) signal propagation environments. Thus, we present a finite-difference computer model to demonstrate a viable approach for predicting the microphysical (microclimate) influences on optical turbulence intensity (C _n ²) around the ARL A_LOT Facility and its surroundings (which consist of multiple building arrays and forests). Our multi-dimensional prototype model begins to address optical turbulence conditions along more complex lines-of-sight and begins to account for inhomogeneities in C _n ² brought about by horizontal changes in landscape, wind flow, temperature, and humidity. For now, the model physics represent advection, pressure gradient, eddy diffusion, and vegetation drag force processes. Simple mechanisms to predict the heat and moisture source terms have also been incorporated. Initial model results have been quite encouraging. The model code is computationally efficient and extremely flexible with regard to modifications and debugging. We anticipate that this kind of computational research will be an important vehicle for investigating C _n ² and related laser-optic propagation effects in complex areas.