21 October 2014 Scintillations in the imaging through turbulence
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Abstract
Fluctuations in the images of scenes viewed over large distances are the most obvious manifestation of the turbulence effects on the imaging of the incoherent objects. While the average or long-exposure imaging is arguably the most well studied topic of the optical propagation in turbulence, and substantial progress was also made in understanding the average short-exposure imaging, the image scintillations for complex extended scenes are not well understood. We discuss some available results of the image scintillation theory and report on some recent progress. We introduce the concept of the scintillation imaging, when unlike the conventional turbulence imaging techniques the variance of the series of images of the scene is calculated and used to gain information either about the object or about the turbulence on the propagation path. The third constraint in the turbulent PSF [1] plays a critical role in the scintillation imaging making scintillation images insensitive to the constant background and emphasizing the areas with higher local contrast. The bilinear structure of the Object-to-Variance (O2V) maps makes it impossible to use the analogues of the PSF or MTF for scintillation images and precludes development of the general theory of scintillation imaging. We discuss the fundamental properties of the O2V kernel and discuss four examples of scintillation images of simple objects. We present the measurement data where colored scintillation images of the edge were obtained. The variance distributions are normalized using the traditional long-exposure images to remove dependence on the object brightness. In this case scintillations are concentrated near the edge and carry information about the turbulence on the imaging path. The amplitude and width of these variance distributions are sensitive to the turbulence level and can be used as passive scintillometer without the need to deploy the laser source and receiver at both ends of the propagation path. Variance images of the object with sinusoidal brightness distribution consists of the uniform background and doublefrequency sinusoidal oscillations. It has the features consistent with turbulent super-resolution originally described in [2]. Namely, for unresolved object oscillating components disappears while the background persevere.
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Mikhail Charnotskii, Mikhail Charnotskii, } "Scintillations in the imaging through turbulence", Proc. SPIE 9242, Remote Sensing of Clouds and the Atmosphere XIX; and Optics in Atmospheric Propagation and Adaptive Systems XVII, 92421Q (21 October 2014); doi: 10.1117/12.2067426; https://doi.org/10.1117/12.2067426
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