DAS/DMAS
Delay-and-Sum / Delay-Multiply-and-Sum
DAS – Delay-and-Sum is the basic image construction algorithm used in total focusing method (TFM) processing. The contribution of each A-scan to the particular location in the image or pixel is obtained by calculating the time delay of signals from each element of the array. The signals are then delayed and added together to obtain a focus at that pixel. However, the image resolution and contrast achievable with DAS are limited.
DMAS – Delay-Multiply-and-Sum is a TFM algorithm that enhances the spatial coherence and suppresses the clutter artefacts that can occur with DAS. Following the delay step, all combinations of in-phase signals are paired and multiplied, before being summed to obtain the amplitude of the pixel. DMAS suppresses the effect of random noise in the A-scans.
For information on DAS / DMAS, see:
www.nrc.gov/docs/ML2321/ML23216A009.pdf
WHAT THE HEC?! articles are not intended to be the definitive account on the topic or acronym in question. Readers’ comments and contributions are welcomed. Email: ndtnews@bindt.org
