Title

Demonstrated resolution enhancement capability of a stripmap holographic aperture ladar system

Date of Award

2012

Degree Name

M.S. in Electro-Optics

Department

Department of Electro-Optics and Photonics

Advisor/Chair

Advisor: Bradly D. Duncan

Abstract

Holographic aperture ladar (HAL) is a variant of synthetic aperture ladar (SAL). The two processes are related in that they both seek to increase cross-range (i.e., the direction of the receiver translation) image resolution through the synthesis of a large effective aperture -- which is in turn achieved via the translation of a receiver aperture and the subsequent coherent phasing and correlation of multiple received signals. However, while SAL imaging incorporates a translating point detector, HAL takes advantage of two-dimensional translating sensor arrays. For the research presented in this article, a side looking Stripmap HAL geometry was used to sequentially illuminate a set of Ronchi ruling targets. Prior to this, theoretical calculations were performed to determine the baseline, single sub-aperture resolution of our experimental, laboratory based system. Theoretical calculations were also performed to determine the ideal modulation transfer function (MTF) and expected cross-range HAL image sharpening ratio corresponding to the geometry of our apparatus. To verify our expectations, we first sequentially captured an over-sampled collection of pupil plane field segments for each Ronchi ruling. A HAL processing algorithm was then employed to phase correct and re-position the field segments after which they were properly aligned through a speckle field registration process. Relative piston and tilt phase errors were then removed prior to final synthetic image formation. By then taking the Fourier transform of the synthetic image intensity and examining the fundamental spatial frequency content, we were able to produce experimental modulation transfer function curves which we could then compare to our theoretical expectations. Our results show that we are able to achieve nearly diffraction limited results for image sharpening ratios as high as 6.43.

Keywords

Resolution (Optics), Imaging systems Image quality, Optical radar, Holography Data processing, Image processing Digital techniques

Rights Statement

Copyright 2012, author

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