Temporal wavelet analysis for deformation and velocity measurement in speckle interferometry

Abstract

When a continuously deforming object is measured by electronic

speckle pattern interferometry (ESPI), the speckle pattern recorded

on a camera sensor changes constantly. These time-dependent

speckle patterns would provide the deformation history of the object.

Various objects are applied with both linearly and nonlinearly varying

loads and speckle patterns are captured using a high-speed CCD camera.

The temporal intensity variation of each pixel on the recorded images

is analyzed by a robust mathematical tool—Morlet wavelet transform

instead of conventional Fourier transform. The transient velocity

and displacement of each point can be retrieved without the necessity of

the temporal or spatial phase unwrapping process. The displacements

obtained are compared with those from a temporal Fourier transform,

and the results show that the wavelet transform minimizes the influence

of noise and provides better results for a linearly varying load. System

error in the wavelet analysis for nonlinear load is also discussed.