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Yang, ZhijunIncoherent Imaging in the Presence of Atmospheric Turbulence and Refractivity
Doctor of Philosophy (Ph.D.), University of Dayton, 2017, 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.

Committee:

Mikhail Vorontsov (Advisor); Partha Banerjee (Committee Member); Edward Watson (Committee Member); Steven Fiorino (Committee Member)

Subjects:

Atmospheric Sciences; Engineering; Optics

Keywords:

incoherent imaging; atmospheric turbulence; refractivity; modulation transfer function; optical mirage

Liu, Yu-JihCentroid angle of arrival temporal power spectrum for spherical wave progation through the turbulent atmosphere between two moving vehicles /
Doctor of Philosophy, The Ohio State University, 1983, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Atmospheric turbulence;Wave-motion

Reinhardt, George WilliamThe spherical wave phase difference temporal power spectra for light beams degraded by a turbulent atmosphere /
Doctor of Philosophy, The Ohio State University, 1979, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Atmospheric turbulence;Wave-motion

Morris, Nathaniel R.Adaptive Optics System Baseline Modeling for a USAF Quad Axis Telescope
Master of Science (MS), Wright State University, 2017, Physics
Atmospheric turbulence has afflicted accurate observations of celestial bodies since man first gazed upon the stars. In this past century, the technology of adaptive optics was invented to help compensate for the optical distortions that atmospheric turbulence causes. As part of that technology, artificial guide stars, wave front sensors, deformable mirrors, and other optical components were developed to correct these wave aberrations. The purpose of this study focuses on the modeling and configuration of an adaptive optics system that is appropriate for the John Bryan Observatory Quad Axis Telescope System (JBO-Q), which is funded by the United States Air Force. Scaling law modeling of site-specific atmospheric parameters using numerical weather data and laser propagation theory was used determination and optimization of some critical system specifications and threshold parameters for this baseline model.

Committee:

Jerry Clark, Ph.D. (Advisor); Jason Schmidt, Ph.D. (Committee Member); Elizabeth Beecher, Ph.D. (Committee Member)

Subjects:

Astronomy; Atmosphere; Atmospheric Sciences; Engineering; Optics; Physics

Keywords:

Adaptive Optics; John Bryan Observatory; Atmospheric Turbulence Compensation; LIDAR; Air Force Research Lab; Fried Parameter; Greenwood Frequency; Rytov Number; Baseline specifications for AO system

Shaari, Wanis A.Measurement of clear-air temperature and velocity spectra and cross spectra and of C²T with two hot-wire anemometers /
Doctor of Philosophy, The Ohio State University, 1984, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Anemometer;Atmospheric turbulence

Mohamed, Fathi Husain AlhadiMitigation of Amplitude and Phase Distortion of Signals Under Modified Von Karman Turbulence Using Encrypted Chaos Waves
Doctor of Philosophy (Ph.D.), University of Dayton, 2016, Engineering
Atmospheric turbulence as an agency affecting the propagation of electromagnetic (EM) waves in different regions of the earth relative to the ground plane has been studied extensively over the past several decades. Mathematical models describing turbulence itself relative to EM waves have been developed by a variety of investigators in the last 50 or more years. It turns out that the majority of these models are essentially in the spatial domain, involving transverse spatial coordinates and their spatial frequency counterparts in the spectral domain. Most turbulence models start out by assuming a random dependence of the medium permittivity on the turbulence. This leads to a random model describing what is commonly referred to as the refractive index power density spectrum. It is well known that propagation through standard atmospheric turbulence creates ripples, random distortions, phase variations and also for monochromatic cases scintillations in the recovered signals. One idea that was proposed to the investigators of this research was that perhaps pre-packaging the EM signal inside a trackable chaos waveform might offer some measure of shielding for the signal even as the overall EM wave passes through turbulence. With this objective in mind, this work began by first establishing standard numerical simulations of EM propagation through homogeneous regions upon passage through a variety of apertures. This standard application involved the use of the Fresnel-Kirchhoff diffraction integral implemented in two ways: (a) as a direct propagation from an object to an image plane, and (b) segmented propagation over uniform incremental layers of the medium in the longitudinal direction. The latter approach was put into place in anticipation of the later introduction of a turbulent layer in the system. Following successful implementation of this technique, turbulence was inserted once again in two different ways: (a) assuming a relatively narrow region of turbulence, modeled as a planar random phase screen derived from the use of the well-known modified von Karman spectrum (MVKS) for refractive index; and (b) the case of an extended random region which is modeled by inserting multiple planar random screens along the propagation path. These initial approaches led to the determination of the resulting scalar output fields numerically derived as complex entities. In the first half of this work, time statistics of the scalar fields were obtained by repeating the simulation multiple times on the basis of an assumed (relatively low) frequency of variation of the turbulence phenomenon (of the order of, say, 20-100 Hz). These time statistics were then incorporated into a transfer function model involving two random processes: (a) the MVKS phase turbulence for which the time statistics were derived as mentioned; and (b) a purely time-dependent chaos wave generated via an acousto-optic (A-O) Bragg cell under feedback, whose first-order optical output is thereby encrypted by an input signal waveform. Use the transfer function approach, cross spectral densities and corresponding cross-correlation functions between the two random phenomena were numerically derived with the final cross correlation product containing the vital message information. Retrieving the message signal from the turbulence-chaos cross correlation product became a prohibitive task, and therefore, even though further investigations are needed, a new approach was developed to complete the intended work. In this approach, a modulated carrier wave which is both time and space-dependent, is propagated through a region of homogeneous space, and upon diffraction through the region, is picked up at the receiver and the embedded message is recovered using appropriate electronics. Thereafter, the same process is repeated in the presence of spatial turbulence, and the recovered signal waveforms are averaged over multiple runs of the simulation representing the time statistics of the turbulence. It is demonstrated that signals recovered under varying degrees of turbulence indeed suffer moderate to severe phase and amplitude distortion, as expected. It must be noted that all numerical simulations reported here are based on strictly near-isoplanatic and paraxial or low propagation angle basis, such that the essential turbulence parameter, C_n^(2 ) is h-independent for all practical purposes. In the final application of this strategy, an encrypted chaos wave riding on an optical carrier is propagated through narrow turbulence of varying strengths, and recovered using a chaos-based heterodyne detection technique. It is shown that indeed encapsulation of the message inside the chaos reduces the distortions in the recovered signal which occur when chaos is not used.

Committee:

Monish Chatterjee, Ph.D. (Advisor); Partha Banerjee, Ph.D. (Committee Member); Eric Balster, Ph.D. (Committee Member); Muhammad Islam, Ph.D. (Committee Member)

Subjects:

Electrical Engineering; Engineering; Optics

Keywords:

Atmospheric turbulence; Gaussian beam; Fresnel-Kirchhoff diffraction integral; modified von Karman model; random phase screen; split-step beam propagation method; acousto-optic chaos; transfer function; cross-correlation, cross-power spectral density

Schumm, Bryce EricEffect of Atmospheric Turbulence on Synthetic Aperture Ladar Imaging Performance
Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Electro-Optics
Synthetic aperture LADAR (SAL) has been widely investigated over the last 15 years with many studies and experiments examining its performance. Comparatively little work has been done to investigate the effect of atmospheric turbulence on SAL performance. The turbulence work that has been accomplished is in related fields or under weak turbulence assumptions. This research investigates some of the fundamental limits of turbulence on SAL performance. Seven individual impact mechanisms of atmospheric turbulence are examined including: beam wander, beam growth, beam breakup, piston, coherence diameter/length, isoplanatic angle (anisoplanatism) and coherence time. Each component is investigated separately from the others through modeling to determine their respective effect on standard SAL image metrics. Analytic solutions were investigated for the SAL metrics of interest for each atmospheric impact mechanism. The isolation of each impact mechanism allows identification of mitigation techniques targeted at specific, and most dominant, sources of degradation. Results from this work will be critical in focusing future research on those effects which prove to be the most deleterious. Previous research proposed that the resolution of a SAL system was limited by the SAL coherence diameter/length r ~_0 which was derived from the average autocorrelation of the SAL phase history data. The present research confirms this through extensive wave optics simulations. A detailed study is conducted that shows, for long synthetic apertures, measuring the peak widths of individual phase histories may not accurately represent the true resolving power of the synthetic aperture. The SAL wave structure function and degree of coherence are investigated for individual turbulence mechanisms. Phase is shown to be an order of magnitude stronger than amplitude in its impact on imaging metrics. In all the analyses, piston variation and coherence diameter make up the majority of errors in SAL image formation.

Committee:

Matthew Dierking (Committee Chair); Joseph Haus (Committee Member); Eric Magee (Committee Member); Bradley Duncan (Committee Member)

Subjects:

Optics; Physics

Keywords:

ladar; lidar; synthetic aperture imaging; synthetic aperture ladar, turbulence; atmospheric turbulence; SAL;

Devasirvatham, Daniel Manoharan JothirajEffects of atomospheric turbulence on microwave and milimeter wave satellite communications systems /
Doctor of Philosophy, The Ohio State University, 1981, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Artificial satellites in telecommunication;Atmospheric turbulence

Power, Jonathan DavidModeling Anisoplanatic Effects from Atmospheric Turbulence across Slanted Optical Paths in Imagery
Master of Science (M.S.), University of Dayton, 2016, Electrical Engineering
When viewing objects over long distances, atmospheric turbulence introduces significant aberrations in imagery from optics with large apertures. We present a model for simulating turbulent effects in imagery using a technique similar to Bos and Roggemann's model [1]. This simulation will support efforts in developing innovative turbulence mitigation techniques and replacing expensive flight tests. The technique implements the commonly used split-step beam propagation method with phase screens optimally placed along the optical path. This method is used to supply a turbulence distorted point spread function (PSF) along the unique, optical path from the object to the camera aperture for each pixel of an image. The image is then distorted by scaling and summing each PSF with the appropriate surrounding area of the corresponding pixel for new pixel values. Very large phase screens have been integrated into the simulation to account for low spatial frequencies and wind speed in video. Additionally, a modified version of Schmidt's method [2] is implemented for estimating statistics for the individual phase screens in the model and for angle spectrum propagation through free space. The proposed model has the capability of simulating over horizontal or slanted paths using the Huffnagel Valley turbulence profile. For verification purposes, analysis of average simulated PSFs for short and long exposures and angle of arrival were compared to theoretical results. Further analysis of simulated error statistics were carried out against varying elevation in the atmosphere.

Committee:

Russell Hardie, Ph.D. (Advisor); Monish Chatterjee, Ph.D. (Committee Member); Barry Karch, Ph.D. (Committee Member)

Subjects:

Atmospheric Sciences; Computer Science; Electrical Engineering; Engineering; Optics

Keywords:

Atmospheric Turbulence; Numerical Simulation; Anisoplanatism; Turbulence in Imagery

Bricker, David A.Analysis of Joint Effects of Refraction and Turbulence on Laser Beam Propagation in the Atmosphere
Master of Science (M.S.), University of Dayton, 2013, Electro-Optics
Experimental data obtained from recently conducted long-range laser beam propagation experiments has revealed inconsistencies with analytic and numeric simulations results based on classical Kolmogorov turbulence theory. This inconsistency may be related with not accounting for refraction effects caused by refractive index variation with elevation and presence of large-scale atmospheric structures which introduce refractive index gradients and can alter the trajectory of optical wave energy flux. In this thesis, atmospheric refraction effects are studied using a ray tracing technique. Due to refraction a ray propagating in the atmosphere doesn't follow a straight line and may not arrive to a desired location. In this thesis the ray tracing technique was applied for analysis of optical propagation over a 150 km propagation path. It was shown that due to refraction the ray trajectory may deviate from the geometric straight line by 60m in the middle of the path. We also considered the impact of refraction on atmospheric propagation of laser beams with different wavelengths (λ=0.532µm, λ=1.064µm, and λ=1.550µm) which were launched at the same angle. Due to the difference in refractive index of air for different wavelengths, the ray's paths follow different trajectories. It was shown that at the end of the propagation path, the distance between ray trajectories can be as long as ~4.1m for the 0.532µm and the 1.064µm rays, and ~4.3m for 0.532µm and 1.550µm rays. Besides traditional ray tracing technique we also introduced a new computational method that allows analysis of combined refraction and turbulence effects on laser beam propagation. In this method, traditional beam propagation using the well-known split step operator method is combined with ray tracing. In this technique the atmospheric volume is represented as a set of thin phase screens that obey Kolmogorov turbulence statistics. The ray tracing technique is applied to describe optical wave propagation between phase screens. At each screen, the turbulence-induced random tip and tilt wave-front phase component is added to the ray angle. In this way, the ray trajectory is no longer deterministic, but it has a turbulence induced uncertainty. It was shown that at the end of a 150km propagation path, the turbulence induced deviation on ray trajectory can be on the order of 5m. These results show that for correct analysis of laser beam propagation over long distances in the atmosphere, refraction and turbulence effects should be considered jointly. The proposed numerical simulation technique allows this joint analysis.

Committee:

Mikhail Vorontsov, Ph.D (Advisor); Partha Banerjee, Ph.D (Committee Member); Paul McManamon, Ph.D (Committee Member)

Subjects:

Optics

Keywords:

Atmospheric Turbulence, Ray Tracing, Numerical Simulation, Laser Beam Propagation