Anisotropic optical turbulence in the stably stratified atmosphere

For various applications involving the propagation of light through the atmosphere, anisotropy of optical turbulence must be accounted for. At this point, however, there is no consensus about how to realistically model anisotropic turbulence. It is well established that at length scales small compared to a certain outer length scale, <i>L</i>₀, fully developed, optical turbulence is locally homogeneous and isotropic and is well described by the Obukhov- Corrsin similarity theory. At scales large compared to L₀, however, the turbulence is usually anisotropic, and the Obukhov-Corrsin similarity theory is no longer valid. <br/> <br/> In this paper, we discuss two questions: first, how to define and predict <i>L</i>₀; and second, how to model the 3D refractive-index spectrum, Φ_n(<i>κ_x, κ_y, κ_z</i>), for wavenumbers comparable to and smaller than 1/<i>L</i>₀. We will address both questions on the basis of classical theoretical concepts and by means of field observations. The classical concepts include Tatarskii’s original definition of <i>L</i>₀, the Richardson criterion, and the Monin- Obukhov similarity theory. Field observations include in-situ measurements by means of ultrasonic anemometer-thermometers and fine-wire turbulence sensors.