Effects of surface-mapping corrections and synthetic-aperture focusing techniques on ultrasonic imaging
Improvements in ultrasonic imaging that can be obtained using algorithms that map the surface of targets are evaluated. This information is incorporated in the application of synthetic-aperture focusing techniques which also have the potential to improve image resolution. Images obtained using directed-beam (flat) transducers and the focused transducers normally used for synthetic-aperture processing are quantitatively compared by using no processing, synthetic-aperture processing with no corrections for surface variations, and synthetic-aperture processing with surface mapping. The unprocessed images have relatively poor lateral resolutions because echoes from two adjacent reflectors show interference effects which prevent their identification even if the spacing is larger than the single-hole resolution. The synthetic-aperture-processed images show at least a twofold improvement in lateral resolution and greatly reduced interference effects in multiple-hole images compared to directed-beam images. Perhaps more importantly, in images of test blocks with substantial surface variations portions of the image are displaced from their actual positions by several wavelengths. To correct for this effect an algorithm has been developed for calculating the surface variations. The corrected images produced using this algorithm are accurate within the experimental error. In addition, the same algorithm, when applied to the directed-beam data, produced images that are not only accurately positioned, but that also have a resolution comparable to conventional synthetic-aperture-processed images obtained from focused-transducer data. This suggests that using synthetic-aperture processing on the type of data normally collected during directed-beam ultrasonic inspections would eliminate the need to rescan for synthetic-aperture enhancement.
- Research Organization:
- EG and G Idaho, Inc., Idaho Falls, ID (United States)
- DOE Contract Number:
- AC07-76ID01570
- OSTI ID:
- 6604704
- Report Number(s):
- EGG-FM-5314; TRN: 81-006264
- Country of Publication:
- United States
- Language:
- English
Similar Records
Effects of surface mapping corrections with synthetic-aperture focusing techniques on ultrasonic imaging
Ultrasonic-image reconstruction with surface mapping and synthetic-aperture techniques