Location

Brunswick, ME

Start Date

1-1-1992 12:00 AM

Description

Broadband Holography has become a powerful tool in computerized non-destructive testing. Interpretation of images, however, is difficult due to the fact that perfect imaging of flaw sizes is impossible until now. The situation is even more complex, since multiple scattering, wave mode conversions, and inhomogeneities in the material give rise to artifacts in the holographic image. Thus, signal and data processing techniques at different levels of the signal flow path may help improve the situation. Within this paper the following methods are discussed: (1) Inverse filtering. Inverse filters improve echo shape and duration. This in turn influences lateral and axial resolutions of the image. Since inverse filtering is known to be an ill posed problem we apply a standard Tychonoff regularization. It turns out to be equivalent to Wiener filtering in its simplest form.; (2) The ALOK i, k-filter. This is a non linear filter mainly used for data reduction purposes during the inspection of large scale components. An attempt is made to at least partly recover the original signal from ALOK data.; (3) Image processing. Using the holographic image of a natural crack we show different image processing techniques. This may be a tool to gain more insight into the flaw size and geometry under test.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

11A

Chapter

Chapter 3: Interpretive Signal Processing and Image Reconstruction

Section

Signal Processing

Pages

903-910

DOI

10.1007/978-1-4615-3344-3_116

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Influence of Filtering Techniques on Holographic Images

Brunswick, ME

Broadband Holography has become a powerful tool in computerized non-destructive testing. Interpretation of images, however, is difficult due to the fact that perfect imaging of flaw sizes is impossible until now. The situation is even more complex, since multiple scattering, wave mode conversions, and inhomogeneities in the material give rise to artifacts in the holographic image. Thus, signal and data processing techniques at different levels of the signal flow path may help improve the situation. Within this paper the following methods are discussed: (1) Inverse filtering. Inverse filters improve echo shape and duration. This in turn influences lateral and axial resolutions of the image. Since inverse filtering is known to be an ill posed problem we apply a standard Tychonoff regularization. It turns out to be equivalent to Wiener filtering in its simplest form.; (2) The ALOK i, k-filter. This is a non linear filter mainly used for data reduction purposes during the inspection of large scale components. An attempt is made to at least partly recover the original signal from ALOK data.; (3) Image processing. Using the holographic image of a natural crack we show different image processing techniques. This may be a tool to gain more insight into the flaw size and geometry under test.