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Proceedings Paper

Measurement of the refractive-index structure constant,C2n, and its profile in the ground level atmosphere by moiré technique
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Paper Abstract

Atmospheric turbulence may have strong impact on astronomical imaging, aerial surveying, terrestrial geodesy, optical ranging, and wireless optical communication. Major effects are beam broadening, irradiance fluctuations (scintillation), and angle-of-arrival (AA) fluctuations. The interesting effects of atmospheric turbulence for optical propagation studies are the variation (gradient and fluctuations) of refractive index. The corresponding refractive- index structure constant, Cn2, is the parameter most commonly used to describe the strength of atmospheric turbulence. Besides, the Modulation Transfer Function of the atmosphere is measurable by Cn2. Good image quality requires Cn2 being as small as possible. In this work we present an easily applicable and accurate method, based on moire technique, for the measurement of Cn2 and its profile in the ground level atmosphere. In this method from a low frequency sinusoidal amplitude grating, installed at certain distance from a telescope, successive images are recorded and stored in a computer. By rotating one of the image by +θ, say 4°, and multiplying its transmission function by the transmission functions of the other images which have been rotated by -θ, a large number of moire patterns are produced. By finding the traces of the moire fringes in the patterns, the fluctuations of the image grating lines are obtained. Which correspond to AA fluctuations distribution. From the AA fluctuations distribution in successive patterns, Cn2 and its profile in vertical direction are deduced. This technique renders to measure some other atmospheric parameters which are discussed in the report.

Paper Details

Date Published: 28 September 2006
PDF: 11 pages
Proc. SPIE 6364, Optics in Atmospheric Propagation and Adaptive Systems IX, 63640G (28 September 2006); doi: 10.1117/12.683873
Show Author Affiliations
Saifollah Rasouli, Institute for Advanced Studies in Basic Sciences (Iran)
Mohammad Taghi Tavassoly, Univ. of Tehran (Iran)

Published in SPIE Proceedings Vol. 6364:
Optics in Atmospheric Propagation and Adaptive Systems IX
Anton Kohnle; Karin Stein, Editor(s)

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