## 4 Result and Discussion
### Measurement with Traveling  
The data obtained by measurements with traveling were equivalent to acquiring data obliquely on the RMS map. At higher traveling speeds, this oblique angle becomes larger, which is supposed to reduce the probability of passing through the attenuation zone, indicating a defect. The traveling measurement was calculated by selecting data from the results shown in Figure 12. Thirteen points were picked up every 0.5 mm in the \(x\)-axis direction according to the experimental conditions for traveling measurements described in Figure 6. When the repetition rate of the laser was 100 Hz and the traveling speed was 0.5 m/min, the distance traveled in the \(y\)-axis direction per irradiation resulted in 0.08 mm. Therefore, the B-scope of the 0.5 m/min traveling measurement can be reproduced by picking up the point every 0.5 mm on the \(x\)-axis and every 0.08 mm on the \(y\)-axis. The cases with 0.25 and 1.0 m/min traveling speeds can be reproduced by picking up the point every 0.04 and 0.16 mm in the \(y\)-axis, respectively. An example of a path on the normalized RMS map at each speed is shown in Figure 14.  
Figure 12: Normalized RMS map with the simulated defect. Figure 13: Schematic diagram showing factors of the RMS value increase/decrease due to defects. The pickup path changes when the start point changes, even at the same traveling speed. A normalized RMS distribution is obtained for each path, and its slope is the detection indicator value for that path. The detection indicator values obtained for each path with a slight shift of the starting point within the analysis range are summarized for 0.25, 0.5, and 1.0 m/min, respectively, as shown in the graph on the right side of Figure 14. The value of the \(y\)-axis is set to the starting position of each cross-section during the traveling measurement. In the case of actual measurement, since one pass irradiation includes 13 points, the following path starts at a point 13 points ahead in the \(y\)-axis direction from the start point of the previous path. Figure 15a,b shows the paths when the measurement starts at \(y=-1.84\) mm and \(y=-1.20\) mm for a traveling speed of 0.5 m/min, and Figure 15c shows the distribution of the detection indicator values calculated for each path. A larger absolute value of the detection indicator means that the defect is more likely to be determined as a defect. In this case, the detection indicator starting the measurement at \(y=-1.84\) mm is about twice that at \(y=-1.20\) mm. Therefore, even when we measure the same defects at the same traveling speed, the ease of defect identification depends on the starting position of the measurement. Similarly, Figure 16 shows a result for a 0.25 m/min traveling speed. Figure 16 also shows that the ease of defect discrimination varies depending on the measurement start position. Once the starting position is determined, the cross-section through the measurement path is also determined. The detection indicator at the cross-section is calculated by picking up the data with equal intervals from the right graph of Figure 14. The interval was 0.54 mm at the traveling speed of 0.25 m/min, 1.08 mm at 0.50 m/min, and 2.16 mm at 1.0 m/min, respectively. The value that had the most significant influence on the judgment of the presence or absence of defects was the value of the largest detection indicator (circled in red in Figure 15c), which also changed depending on the starting position of  
Figure 14: Difference of paths by traveling speed and distribution of largest slope. Figure 15: Change in the RMS distribution with a change in measurement position at 0.5 m/min. (**a**) Starting at \(y=-1.84\) mm. (**b**) Starting at \(y=-1.20\) mm. (**c**) Detection indicator distribution starting at \(y=-1.84\) mm, \(y=-1.20\) mm. the measurement. Therefore, it was found that one of the reasons for the variation in the indicators in our previous proposed defect detection method is the change in the indicators with the difference in the scanning position relative to the defect.