Application of wavelet image processing for ultrasonic gauging

A wavelet transform image decomposition technique was utilized for compression and analysis of the ultrasonic images obtained by a computerized ultrasonic gauging system (CUGS). CUGS can generate very precise topographical maps of the outer and inner surfaces of tubes during various stages of manufacture and life-cycle of the parts. Measurements of the tube dimensions are obtained with a resolution of 2.5 micrometers and accuracies of the order to 10 micrometers or better. A typical output of CUGS is an ultrasonic image, in which the horizontal and vertical axes represent the axial and angular position of the part, respectively. Wavelet-based image analysis has been utilized to obtain representations of the same image with different resolutions and to enhance image features such as erosion pattern without the loss of localization. In the application discussed CUGS is utilized to map the wear of the internal surface of steel tubes, before and after exposure to extreme environments involving temperature, pressure, corrosive gases and mechanical forces.