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Degree

Master of Science (M.S.), University of Dayton, Electro-Optics, 2012.

Abstract

The cross-range resolution of a laser radar (ladar) system can be improved by synthesizing a large aperture from multiple smaller sub-apertures. This aperture synthesis requires a coherent combination of the sub-apertures; that is, the sub-apertures must be properly phased and placed with respect to each other. One method that has been demonstrated in the literature to coherently combine the sub-apertures is to cross-correlate the speckle patterns imaged in overlapping regions. This work investigates the effect of low signal to noise ratio (SNR) on an efficient speckle cross-correlation registration algorithm with sub-pixel accuracy. Specifically, the algorithms ability to estimate relative piston and tilt errors between sub-apertures at low signal levels is modeled and measured. The effects of these errors on image quality are examined using the modulation transfer function (MTF) as a metric. The results demonstrate that in the shot noise limit, with signal levels as low as about 0.02 signal photoelectrons per pixel in a typical CCD, the registration algorithm estimates relative piston and tilt accurately to within 0.1 radians of true piston and 0.1 waves of true tilt. If the sub-apertures are not accurately aligned in the synthetic aperture, then the image quality degrades as the number of sub-apertures increases. The effect on the MTF is similar to the effects due to defocus aberrations.

Subject Headings

Engineering; Optics; Remote Sensing; Scientific Imaging

Keywords

LADAR; Synthetic Aperture Registration; SNR; Speckle Cross-Correlation; MTF; Spatial Heterodyne

Committee / Advisors

Edward Watson, PhD (Advisor)
Matthew Dierking, PhD (Committee Member)
David Rabb, PhD (Committee Member)

Pages

117p.

Document number: dayton1355245759
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=dayton1355245759

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