Ultrasonic array imaging for immersion non-destructive testing

One of the applications of advanced array signal processing is immersion ultrasonic non-destructive testing (NDT), where a solid test sample and an array of transducers are immersed in water, for the purpose of imaging the test sample. To do so, the knowledge of the shape of the upper surface of the test sample is needed. We model the interface between water and the solid as an incoherently spatially distributed reflector. We then develop a covariance fitting based approach to estimate the parameters of the shape of the upper surface of the test sample. With the knowledge of the estimated shape of this surface, we use the same approach to estimate the parameters of the shape of a crack inside the test sample. Numerical simulations are conducted to show the accuracy of the proposed approach.