Frequency-wavenumber migration of ultrasonic data

In ultrasonic nondestructive evaluation (NDE), the depth of the image is us ually calculated by multiplying the traveling time of the echoes with the v elocity of the medium. If the flaw is not a horizontal plane, the flaw imag es may be distorted and mislocated. Although the lateral resolution and siz ing accuracy of the flaw image can be improved using the digital signal pro cessing methods, e.g., the utilization of the blocking filter or deconvolut ion filter, these methods do a little favor about the distortion and misloc ation problems. The migration, an image-processing method used widely in re flection seismology, is introduced to process the ultrasonic data in this s tudy. Since the signals are coherent and the noises are random, the flaw im age can be transformed from its apparent position to the true position usin g the migration method and the resolution of the image may be improved. Not only the real positions of the oblique cracks can be found upon applying t he frequency-wavenumber (F-K) migration to process ultrasonic data, but, in addition, the dimensions of the flaws can be estimated more accurately. Re sults presented in this study show that the migration method can be applied successfully to the ultrasonic data processing and can improve the quality of ultrasonic image in both size and location of the flaws.