Characterization of High Altitude Turbulence for Air Force Platforms

Upper tropospheric and stratospheric turbulence (altitudes ∼ 12-25 km) is an atmospheric phenomenon that has a significant impact on many DoD operations. In particular, optical turbulence (i.e., high frequency fluctuations in the temperature fields) can be a limiting factor in laser propagation for both weapon (e.g., Airborne Laser) and optical communication systems. Optical turbulence along a laser’s path acts to defocus the beam and thus reduces the energy per unit area on a target. When used for visible spectrum high-band width communications, strong optical turbulence can cause significant data dropouts. At the altitudes between 12 and 25 km the atmosphere is generally stably stratified with embedded optically turbulent layers on the orders of 1 to 100 m thick in the vertical and tens to hundreds of km long in the horizontal. While there is a need for real-time forecasts of high altitude turbulence, the vertical scale of the phenomena precludes its explicit depiction by operational numerical weather prediction models. The current approach is to use statistical parameterizations relating vertical temperature gradients and wind shear to optical turbulence (i.e., Dewan et al. 1993; Walters and Miller 1999; Jackson 2004). However none of these techniques come close to fully representing the needs of DoD (e.g., Ruggiero and Debenedictis 2002). While Direct Numerical Simulations (DNS) and for some cases Large-Eddy Simulations (LES) have the ability to explicitly resolve atmospheric turbulence, they are not currently practical for real-time applications due to their computational intensive nature.