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Incoherent Imaging in the Presence of Atmospheric Turbulence and Refractivity

Yang, Zhijun
http://rave.ohiolink.edu/etdc/view?acc_num=dayton1500284170323378

Abstract Details

2017, Doctor of Philosophy (Ph.D.), University of Dayton, Electro-Optics.
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 Cn2 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.
Mikhail Vorontsov (Advisor)
Partha Banerjee (Committee Member)
Edward Watson (Committee Member)
Steven Fiorino (Committee Member)
75 p.
Atmospheric Sciences; Engineering; Optics
incoherent imaging; atmospheric turbulence; refractivity; modulation transfer function; optical mirage

Recommended Citations

Citations

  • Yang, Z. (2017). Incoherent Imaging in the Presence of Atmospheric Turbulence and Refractivity [Doctoral dissertation, University of Dayton]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1500284170323378

    APA Style (7th edition)

  • Yang, Zhijun. Incoherent Imaging in the Presence of Atmospheric Turbulence and Refractivity. 2017. University of Dayton, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=dayton1500284170323378.

    MLA Style (8th edition)

  • Yang, Zhijun. "Incoherent Imaging in the Presence of Atmospheric Turbulence and Refractivity." Doctoral dissertation, University of Dayton, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1500284170323378

    Chicago Manual of Style (17th edition)

dayton1500284170323378
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This open access ETD is published by University of Dayton and OhioLINK.