Wavelet transform for detection of partial fringe patterns induced by defects in nondestructive testing of holographic interferometry and electronic speckle pattern interferometry

Holographic interferometry (HI) and electronic speckle pattern interferometry (ESPI) are widely used in nondestructive testing (NDT). In the HI and ESPI measurement techniques, the deformations are made visible as fringe patterns while an inspected sample is loaded. Defects will lead to typical local deformations deviating from the global deformation. To achieve automatic detection of the defect characteristics, the wavelet transform (WT) method is used. Wavelets can be used to generate a multiresolution analysis of a signal and they are very sensitive to the changes in a transient signal or an abrupt signal if suitable wavelets are chosen. These changes correspond to the partial fringe patterns caused by the local defects in HI and ESPI nondestructive testing. We demonstrate how the Morlet wavelet is used to detect the defect-induced partial fringe patterns from the global fringe pattern in HI and the ESPI nondestructive testing. (C) 2000 Society of Photo-Optical instrumentation Engineers. [S0091-3286(00)01710-4].