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17 June 2009 Evaluation of aliasing influence on the performance of hybrid optical-digital speckle correlator
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The optical speckle-displacement correlator based on hybrid optical-digital joint transform correlator architecture with digital first and optical second stage is used to determine correlation peak position with subpixel accuracy without usage of intricate interpolation algorithms. Experimental setup for realization of the optical speckle-displacement correlation technique was constructed on basis of a digital Fourier processor allowing joint power spectrum median and ring median binarization and an optical Fourier processor. Speckle patterns of steel beam specimen (steel 45) with different maximum spatial frequencies were recorded. As one of the joint transform correlator main parameters is distance between fringes at correlator frequency plane, comparison of optical speckle-displacement correlator performance for different values of speckle pattern maximum spatial frequency for the given joint power spectrum modulation was performed. Experimental results have shown that the signal-to-noise ratio (SNR) increases steadily while the maximum frequency of speckle pattern multiplied Fourier spectrum is reaching the Nyquist frequency fN. The analysis of the speckle pattern with frequencies higher than Nyquist frequency has shown that the SNR growth is continued to the some boundary frequency fB>fN after which the SNR is fallen sharply. Thus, the influence of aliasing on the correlator performance was studied and the best correspondence between value of speckle pattern maximum spatial frequency and distance between fringes at the correlator frequency plane was found.
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Leonid I. Muravsky, Olexander M. Sakharuk, and Pavel V. Yezhov "Evaluation of aliasing influence on the performance of hybrid optical-digital speckle correlator", Proc. SPIE 7389, Optical Measurement Systems for Industrial Inspection VI, 73892I (17 June 2009);


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