Date of Award

9-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Engineering Physics

First Advisor

Steven T. Fiorino, PhD

Abstract

The effect of turbulence on a long range imaging system manifest as an image blur effect usually quantified by the phase distortions present in a system. The blurring effect is conceivably understood on the basis of measured strength of atmospheric turbulence profiled within the propagation volume. One method for obtaining a turbulence strength profile is by use of a dynamically ranged Rayleigh beacon system that exploits strategically varied beacon ranges along the propagation path, effectively deducing estimates of specific path segment contributions of the blurring aberrations affecting an optical imaging system. A system utilizing this technique has been designed, and a prototype has been constructed for testing. This system is named TARDIS, which stands for Turbulence and Aerosol Research Dynamic Interrogation System. The TARDIS is an optical sensing system that is based on dynamically changing the range between the collecting sensor and Rayleigh beacon during a static period of relatively unchanging turbulence-induced wavefront perturbations. A notional collecting scenario consists of beacons where the air molecule and aerosol particle backscatter images captured at different distances from the collecting aperture based on laser pulsing and camera shutter speeds. Obtaining measurement based estimates of the turbulence strength profile from TARDIS is based around collating segmented refractive index structure parameter, , values traced to specific layers of the atmosphere. These values are developed from Fried parameter segments, , which are deduced from neighboring measurements on the Shack-Hartmann wavefront sensor. A single value of the Fried parameter is estimated from the mean of the variance of the phase present on the sensing system’s collecting aperture. The mean of the variance of the estimated phase across the aperture is built from the zonal tilt tiles reconstructed from the Shack-Hartmann wavefront sensor measured gradients. This paper provides the foundational theory for understanding atmospheric turbulence, provides reference to currently available turbulence estimation techniques, and provides details towards TARDIS, the tomographic turbulence estimation methodology, and analysis of initial proof of concept data collected.

AFIT Designator

AFIT-ENP-DS-21-S-036

DTIC Accession Number

AD1149665

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