Characterisation of real defects is one of the main challenges in ultrasonic non-destructive testing (NDT), especially for small defects having irregular shapes. Traditional methods such as ultrasonic array imaging are limited by the image resolution, and in this paper, we consider using the scattering matrix which is extractable from the full matrix of transmit–receive array data. We describe a procedure in which the experimental measurements are used to perform characterisation and reveal the associated uncertainties. Moreover, we explore the performance of this characterisation procedure and propose a robust defect characterisation approach. The performance of the proposed approach is studied experimentally, and the sizing errors are small (within 0.09$\lambda$ or 0.23mm for fatigue cracks at 2.5 MHz, and within 0.38$\lambda$ or 0.24mm for volumetric defects in an additive manufactured specimen at 10 MHz). In addition, reliable estimation of defect angle/width is achieved.

真正缺陷的表征是超声无损检测（NDT）的主要挑战之一，尤其是对于形状不规则的小缺陷。诸如超声阵列成像之类的传统方法受到图像分辨率的限制，在本文中，我们考虑使用可从发射-接收阵列数据的完整矩阵中提取的散射矩阵。我们描述了一种程序，在该程序中，将实验测量值用于执行表征并揭示相关的不确定性。此外，我们探索了该表征过程的性能，并提出了一种鲁棒的缺陷表征方法。通过实验研究了该方法的性能，并且尺寸误差很小（在0.09以内）$\lambda$ 或0.23mm（用于2.5 MHz且0.38以内的疲劳裂纹）$\lambda$或0.24mm（对于在10 MHz下添加的人造样品中的体积缺陷）。另外，可以可靠地估计出缺陷角度/宽度。