Measurements of Laser-Beam Scintillation in the Atmosphere

Abstract

Measurements have been made of the scintillation of a laser beam after propagating over an 8-km path near the ground. The measurements were made with collection apertures ranging from 1 mm to 1 m in diameter. The probability distribution of the scintillation was found to be log-normal for all collector diameters. The log-normal variance decreased smoothly for diameters from 1 mm to about 10 cm, but showed no decrease between 10 cm and 1 m. A hypothesis is offered which explains those results which are anomalous in terms of present theories. Measurements of the log-normal variance were made over extensive periods on three days, during winter, spring, and summer. From these the atmosphere’s refractive-index structure constant, CN2, was computed. Values of CN2 were found to be fairly constant over the full range of measurements, falling between 3 and 6×10−15m−23, except near sunrise and sunset, when values of about 1×10−15m−23 were more typical.