# Towards Explainable Augmented Intelligence (AI) for Crack Characterization
## 4 Training AutoNDE
### Training AutoNDE on DPS Data  
It has been established by trial and error that the best images of the specimen used in DPS experiment (see Figure 1) could be obtained by specifying its thickness as 29.5 mm and distance from the probe to the specimen, as 12.5 mm. In other words, it has been established that the 0.5 mm difference in these parameters has a significant effect on the image quality. The number of array elements and length of A-scan have been already specified above as K = 128 and N = 800. The optimal length of the \"partial probe\" has been established by trial and error to be 25 elements, covering the aperture of 20 mm. This aperture is large with respect to the typical length of the longitudinal wave: Given the longitudinal speed within the steel specimen of 5.89 km/s and the central pulse frequency of 5 MHz, this typical length is 1 mm. Similarly, it has been found that enough information could be collected with 25 images, \(D_{m}\) varying between 0 to 24 array elements. No interpretable images were produced for larger values of \(D_{m}\). Finally, whatever the dataset, quality results have been obtained for the same region of interest. This has been chosen as the central region, roughly 20% of the area underneath the probe, symmetrical with respect to the probe center. The resulting estimates of notch characteristics are compared to their known experimental values in Table 1. The experimental values were established using standard approaches used in experiments of this nature, see, e.g., [1]. Table 1 shows that depths of the notches in DPS data could be estimated with the error of up to 2 mm (in one instance, 3 mm), and orientations--with the error of 5-10\({}^{\circ}\). We note here that assuming the inspection surface plane would produce similar estimates for most of the notches but the second entry would be 7 mm in extent, located at 1 mm depth, oriented at 75\({}^{\circ}\) and the fourth entry would be 7 mm in extent, located at 0 mm depth, oriented at 125\({}^{\circ}\). It follows that results are more reliable when small surface undulations are taken into account. Typical MTFM images are presented in Figure 7: both Figure 7a,b contain three bright spots, with the two brightest ones joined by a thin yellow line. However, while the top spot is bright in both images, in Figure 7a the brightest lower spot is found at a distance of 4 mm \begin{table}
\begin{tabular}{c c c c c} \hline \hline \begin{tabular}{c} **Inspection Surface/** \\ **Approximate Notch Depth/** \\ **Notch Distance from Edge** \\ \end{tabular} & \begin{tabular}{c} **Report** \\ **Quality/Comments** \\ **Quality/Comments** \\ \end{tabular} & \begin{tabular}{c} **Exent,** \\ **in mm Est/Exp** \\ \end{tabular} & \
\begin{tabular}{c} **Orientation,** \\ **in deg Est/Exp** \\ \end{tabular} &
\begin{tabular}{c} **Depth, in** \\ **mm Est/Exp** \\ \end{tabular} \\ \hline \hline Flatside/Buried/24 mm & 60\% & 9/10 & 105/110 & 8/5 \\ \hline Flatside/Buried/62 mm & 40\% & 6/5 & 105/110 & 5/5 \\ \hline Flatside/Buried/113 mm & 40\% & 12/10 & 90/90 & 5/5 \\ \hline Flatside/Buried/149 mm & 20\%hc & 5/5 & 85/90 & 6/5 \\ \hline Flatside/Breaking/25 mm & 60\% & 6/5 & 80/90 & 0/0 \\ \hline Flatside/Breaking/64 mm & 90\% & 11/10 & 90/90 & 0/0 \\ \hline Flatside/Breaking/113 mm & 60\% & 7/5 & 100/110 & 0/0 \\ \hline Flatside/Breaking/150 mm & 90\% & 12/10 & 110/110 & 1/0 \\ \hline Notchside/Buried/24 mm & 60\% & 11/10 & 110/110 & 5/5 \\ \hline Notchside/Buried/62 mm & 70\% & 6/5 & 110/110 & 5/5 \\ \hline Notchside/Buried/113 mm & 30\% & 12/10 & 90/90 & 4/5 \\ \hline Notchside/Buried/149 mm & 30\% & 5/5 & 80/90 & 3/5 \\ \hline Notchside/Breaking/25 mm & 40\% & 5/5 & 100/90 & 1/0 \\ \hline Notchside/Breaking/70 mm & 30\%hc & 8/10 & 90/90 & 2/0 \\ \hline Notchside/Breaking/113 mm & 30\% & 5/5 & 115/110 & 1/0 \\ \hline Notchside/Breaking/155 mm & 50\% & 8/10 & 115/110 & 2/0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The DPS data set: Estimated (est) and experimental (exp) crack characteristics.