Effects of atmospheric turbulence on optical propagation

The optical refractive index of the atmosphere depends on temperature, pressure, and humidity. Naturally occurring variations of these quantities, with scales of a few centimeters and associated with atmospheric turbulence, cause optical scintillation, image distortion, and laser beam broadening. The meteorological conditions that influence the occurrence of this optical turbulence are reviewed. The optical significance of turbulence at various heights in the atmosphere is discussed. The differences between these optical effects and the corresponding phenomena at radio wavelengths are pointed out. While beam broadening increases indefinitely with the strength of optical turbulence, scintillation saturates and eventually decreases with increasing turbulence. This important effect is discussed and a phenomenological theory that explains it is given. Estimates are given of the limitations imposed by atmospheric turbulence on various types of optical systems. The techniques that can be used to measure optical turbulence are discussed.