Recent developments of optical turbulence measurement techniques

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 (theta(0)), and the Rytov variance (sigma(2)(chi)). A historical perspective of these methodologies and instrumentation is presented and both in situ and remote sensing techniques are discussed. Recent designs of 5 meters are shown. Of particular interest is the development of techniques to derive turbulence parameters such as C-n(2), the eddy dissipation rate (epsilon), 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.