Characterization of atmospheric optical turbulence for laser propagation

The performance of imaging or transmission systems is limited by atmospheric inhomogeneities and fluctuations. Temperature and pressure variations associated with turbulent eddies cause random fluctuations of the refractive index structure constant (C²_n), which distort optical waves. The distortions may lead to significant blurring, scintillations, broadening and wander of the laser beam. High resolution nested numerical simulations are used to predict and characterize Optical Turbulence (OT) induced by jet streams and gravity waves under various local atmospheric conditions. Non-homogeneous, anisotropic, non-Kolmogorov patchy shear-stratified turbulence in the Upper Troposphere and Lower Stratosphere (UTLS) requires that a fine mesh be used to resolve stiff velocity and temperature gradient profiles. Computational approach is based on nesting and refined vertical gridding in nested mesoscale/microscale codes. This methodology is applied to the analysis of field data from observations. Local distributions of simulated optical turbulence in the UTLS are obtained using very high resolution explicit simulations and parametrization formula. They show strongly laminated structures with thin layers of high values of the refractive index. These optical layers are characterized by steep vertical gradients of potential temperature and are located at the edges of relatively well mixed regions produced by shear instabilities and wave breaking.