Spatial Correlation Coefficient Images for Ultrasonic Detection (Preprint)
MISSOURI UNIV-COLUMBIA DEPARTMENT OF MECHANICAL AND AEROSPACE ENGINEERING
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In ultrasonics, image formation and detection are generally based on signal amplitude. In this paper, we describe an amplitude independent approach for image formation and detection based on the similarity of adjacent signals. Signal similarity is quantified in terms of the correlation coefficient calculated between A-scans digitized at adjacent measurement positions. Correlation coefficient images are introduced for visualizing the similarity in measured A-scans. In backscatter, the approach reveals defect signals buried in noise by showing regions of increased correlation. In pitch-catch or thru-transmission, the approach reveals defects by showing regions of decreased correlation due to signal distortion caused by interaction of the beam field with the defect. Correlation coefficient and C-scan images are shown to demonstrate flat-bottom-hole detection in a stainless steel annular ring and crack detection in an aluminum aircraft structure. Simulated data are used to show the detection of planar defects at very low signal-to-noise ratio.
- Acoustic Detection and Detectors