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Incoherent Imaging in the Presence of Atmospheric Turbulence and Refractivity

机译：存在大气湍流和折射的非相干成像

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摘要

Atmospheric turbulence, associated with its refractive-index inhomogeneities (refractivity), may severely affect long range incoherent images formation. Example of this impact includes image blurring, motion, warping and anisotropic geometrical distortions. Currently, the effects of turbulence and refractivity on image formation are considered as being mutually independent and analysed separately using the Fresnel diffraction (wave-optics) and geometrical optics (ray tracing) approaches, respectively. Such independent treatment of turbulence and refractivity effects have certain limitations. Atmospheric refractivity may result in significant deviations of optical wave propagation direction. This effect is commonly referred as the ray bending which, in turn, may lead to a change in turbulence characteristics such as the refractive index structure parameter C2n that is commonly considered as a function of altitude h above the ground. Correspondingly, optical wave refraction, especially in extended-range imaging scenarios, could affect the turbulence-induced optical aberrations.;In this work, we analyze the incoherent image formation in atmosphere in the presence of both atmospheric turbulence and refractivity using numerical simulations based on the brightness function (BF) technique.;Using the BF technique, the incoherent imaging system modulation transfer function (MTF) estimation is performed via direct numerical analysis of visibility of sine-test patterns of different spatial frequencies. The test patterns are assumed to be imaged through a volume medium with turbulence and refractivity-induced refractive index inhomogeneities. The major effects observed in numerical simulations, include the spatial frequency shift between frequency of a sine-test object and its image, and spatial non-uniformity of the sine-pattern image distortion which is referred as the refractivity-induced image anisoplanatism. Both effects depend on the location and strength of the localized refractive index structure with respect to the imaging (wave propagation) geometry. The MTFs corresponding to distributed (volume) turbulence with and without atmospheric refractivity are also compared.;Next, the joint impact of atmospheric turbulence and inverse temperature layer (ITL) on optical mirage formation is analyzed. The dependency of both desert- (superior) and ocean-type (inferior) mirage image formation on ITL characteristics (temperature inversion and location of the ITL) have been studied. The impact of atmospheric turbulence strength on mirage image qualities is also analyzed.;Finally, a numerical analysis is conducted to study the impact of localized refractive index inomogeneites on image quality. It is shown that image quality strongly depends on atmospheric turbulence strength and locations along the optical path. To characterize this impact, two metrics are proposed and developed to measure the image quality as a function of turbulence strength and location. The impact of inverse temperature layer on the developed image quality metrics are also studied.
机译：大气湍流及其折射率不均匀性（折射率）可能会严重影响远距离非相干图像的形成。这种影响的示例包括图像模糊，运动，翘曲和各向异性几何变形。当前，湍流和折射率对图像形成的影响被认为是相互独立的，并分别使用菲涅耳衍射（波动光学）和几何光学（光线追迹）方法进行了分析。这种对湍流和折射率效应的独立处理具有一定的局限性。大气折射率可能会导致光波传播方向发生重大偏差。这种影响通常称为射线弯曲，继而可能导致湍流特性发生变化，例如通常被视为地面高度h的函数的折射率结构参数C2n。相应地，光波折射，尤其是在远距离成像场景中，可能会影响湍流引起的光学像差。在这项工作中，我们使用基于的数值模拟分析了在大气湍流和折射同时存在的情况下大气中非相干图像的形成。使用BF技术，通过对不同空间频率的正弦测试模式的可见性进行直接数值分析，可以进行非相干成像系统调制传递函数（MTF）估计。假设测试图案是通过具有湍流和折射率引起的折射率不均匀性的体积介质成像的。在数值模拟中观察到的主要影响包括：正弦测试对象的频率与其图像之间的空间频移，以及正弦图样图像失真的空间不均匀性，这种不均匀性被称为折射率引起的图像各向异性。两种效果都取决于局部折射率结构相对于成像（波传播）几何形状的位置和强度。还比较了具有和不具有大气折射率的分布（体积）湍流的MTF。接下来，分析了大气湍流和逆温度层（ITL）对海市rage楼形成的联合影响。研究了沙漠（上层）和海洋型（下层）海市image楼图像形成对ITL特性（ITL的温度反转和位置）的依赖性。最后分析了大气湍流强度对海市rage楼图像质量的影响。最后，通过数值分析研究了局部折射率不均匀对图像质量的影响。结果表明，图像质量在很大程度上取决于大气湍流强度和沿光路的位置。为了表征这种影响，提出并开发了两个度量标准，以测量作为湍流强度和位置的函数的图像质量。还研究了逆温度层对已开发图像质量指标的影响。

著录项

  • 作者

    Yang, Zhijun.;

  • 作者单位

    University of Dayton.;

  • 授予单位 University of Dayton.;
  • 学科 Atmospheric sciences.;Engineering.;Optics.
  • 学位 Dr.Ph.
  • 年度 2017
  • 页码 96 p.
  • 总页数 96
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 人类学;
  • 关键词

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