Verification of a Kirchhoff scattering model for imaging pits on a water/steel interface with a focused transducer

Ultrasonic simulators based on the Kirchhoff approximation, a single-scattering approximation, allow imaging geometries with three-dimensional irregular surfaces. Cracked or pitted surfaces can be simulated orders of magnitude faster than alternative general surface simulators such as those based on the finite difference method. Numerical and laboratory tests of the accuracy of the Kirchhoff approximation for simulating ultrasonic scattering from small pits in a steel plate show that the approximation is accurate for geometries where specular or diffracted waves are dominant. For small pits, where strong multiple scattering is present, the simulator still accurately describes the early time behavior of the received voltage waveforms