Image Processing and Analysis of Digital Speckle Pattern Interferometric Images for Monitoring / Surface Vibration / Tilt

Monitoring of vibrations of surfaces is of great interest for many potential applications [1-61. The importance of optical techniques for determination of vibration analysis of mechanical structures stem froin the fact that they enable ineasureinent of vibrational motion without mechanical contact. Optical techniques caii be employed to measure the vibrations of objects s idi as aeroplanes, automobiles and other mechanical components etc. [5-14]. During tlie last twenty years literally hundreds of studies have been carried out in this field. These studies caii be divided into three categories based on optical technique employed: Holography, Moire, Speckles and other optical techniques. Each of these methods can be applied in time averaged, pulsed and strobosqopic modes of operation. In all these methods the results obtainedderived from an intensity map show that the area at rest during the exposure time appears brightest. From such maps the amplitude of tlie displacement of a vibrating object may be determined. None of these methods, however can be wed to ineasnre real-time non-periodic motion. Such nonperiodic motions are of great importance in deterinination of transient effects and also characterisation of vibrational motions which have complex(i.e. inulti-frequency) and time varying power spectrum (for example speakers responding to music). The sensitivity and accuracy provided by interferometric tec1iniqu:s have always been attractive [15]. In this paper we present digital speckle pattern interferometric system to monitor surface vibrations and out-of-plane tilt.