Accession Number:
ADA608962
Title:
Signal-to-Noise Ratio Effects on Aperture Synthesis for Digital Holographic Ladar
Descriptive Note:
Interim rept. 1 Jan 2011-31 Oct 2012
Corporate Author:
AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH SENSORS DIR
Personal Author(s):
Report Date:
2014-08-01
Pagination or Media Count:
80.0
Abstract:
The cross-range resolution of a 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 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 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.
Descriptors:
Subject Categories:
- Lasers and Masers
- Holography
- Optical Detection and Detectors
- Radiofrequency Wave Propagation