*5.3. Detection of Delamination*

The detectability of delaminations during both daytime and nighttime on the sunny day are pointed out in Figure 18. The black filled-in squares and red unfilled-in circles represent detected and undetected delaminations respectively. It should be noted that delaminations with depths equal to or higher than 5.0 cm and the given sizes in this study were not detected. Thus, the red dashed line is used to divide the graph into two regions: detectable and undetectable regions, considering delaminations with depths equal to or smaller than 4.0 cm.

In Figure 18, the horizontal axis shows the delamination depth while the vertical axis is for the delamination size; hence the detectability of delaminations can be indicated in terms of WTDR. Certain conclusions can be given based on Figure 18 and information presented under Section 5.2 as follows.

For delaminations with depths higher than 4.0 cm (F-D1 to F-D12) on both sunny and cloudy days (day 3 and day 4): All delaminations could not be detected at any given time of the experiment period. This implies that it is impossible to identify delaminations with depths deeper than 4.0 cm and WTDRs equal to or smaller than 2.25 under the conditions of this study.

For delaminations with depths equal to or smaller than 4.0 cm (B-D1 to B-D12) on the sunny day (day 1): In the daytime, the dashed line has a slope of 1.9 that implies a delamination whose size is not smaller than 1.9 times its depth (WTDR ≥ 1.9) may be detected (Figure 18a). However, a delamination with a WTDR of 1.9 could not be identified during the nighttime (Figure 18b). The WTDR during the nighttime should be at least 2.5 for a delamination to become detectable (the dashed line with a slope of 2.5).

For delaminations with depths equal to or smaller than 4.0 cm (B-D1 to B-D12) on the rainy day (day 2), delamination could hardly be identified.

**Figure 18.** Detected and undetected delaminations on the sunny day (day 1 and day 3): (**a**) daytime; (**b**) nighttime.
