Analysis of multiwavelength observations of optical scintillation

Abstract

Results are presented from an experimental study of the effects of wavelength, range, and thermal turbulence intensity on the laser scintillation magnitude, represented by the log-intensity standard deviation, sigma. During the first phase of the study, intensity fluctuations at 0.6328 microm were measured over a nearground horizontal path for six ranges out to 7.6 km. Similar measurements were made during the second phase at four ranges out to 2.5 km for three wavelengths: 0.4880 microm, 0.6328 microm, and 1.064 microm. A 5-mm diam receiver aperture was used in all cases. During both phases, concurrent measurements of the refractive-index-structure function C(n) were obtained. It was observed that the measured scintillation (sigma(m)) at 0.6328 microm reached a mean maximum of 1.05 when the theoretical Tatarski value (sigma(t)) was 2.5 and then decreased at larger sigma(t) to a value about 0.5, where the scintillation showed evidence of leveling off. The mean maximum scintillation at 0.4880 microm is 1.09, and at 1.064 microm it is 0.82; the ratios of the maxima are well approximated by the minus seven-twelfths power of the wavelength. At large sigma(t) values, the scintillation depends only slightly on wavelength.