Establishing the Limits of Validity of the Superposition of Experimental and Analytical Ultrasonic Responses for Simulating Imaging Data.

The superposition of experimental and analytical data is useful for simulating ultrasonic images of defects in samples containing high levels of coherent structural noise. This technique assumes that the superposition of the response of a defect in a homogeneous medium with that of a heterogeneous, defect-free medium is identical to the response of the same defect embedded in the heterogeneous medium. This implies a single-scattering process. Previous experimental work demonstrated successful use of the technique but only over a limited range of defect signal-to-noise ratios (SNRs). However, there was a concern that it might not remain valid at low SNR due to, for example, multiple-scattering effects. This paper shows that this technique provides accurate results over the full range of SNRs of defects where the defect is discernible from image noise. The technique is, therefore, suitable for simulating any inspection where ultrasonic imaging is an appropriate method of nondestructive evaluation.