Recent developments of optical turbulence measurement techniques

摘要

With the advent of new developments in tracking, pointing, and compensation of laser beams over the past several years, a requirement has been established for increasing knowledge of optical turbulence along the propagation path. This has stimulated the development of new methodologies to sense the refractive index structure parameter (C_n~2 ) and derived parameters such as the transverse coherence length (r_0), the isoplanatic angle (θ_0), and the Rytov variance (σ_x~2 ). A historical perspective of these methodologies and instrumentation is presented and both in situ and remote sensing techniques are discussed. Recent designs of r_0 meters are shown. Of particular interest is the development of techniques to derive turbulence parameters such as C_n~2 , the eddy dissipation rate (ε), the inner scale (l_0), and the outer scale (L_0). Observational results are discussed using sodar and radar of phenomena generating turbulence including gravity wave activity, jet streams, Kelvin-Helmholtz instabilities, convection, and frontal activity. Both frequency modulated-continuous wave (FMCW) and mesosphere-stratosphere-troposphere (MST) radar are discussed. New techniques and results are shown examining if the turbulent atmosphere is truly Kolmogorov (how often is the structure function represented by the r~(2/3) law), stationary, isotropic, and homogeneous. Emerging techniques for sensing turbulence such as optical path profilers and lidar are discussed.