## 5 Summary and Implication  
This study proposes a real-time source localization using acoustic emission (AE) via scaled laboratory experiments. The algorithm, composed of the automatic single and two-stage AIC picker and Simplex method, was developed and its damage-source localization accuracy was examined with  
Figure 11: The normalized waveforms generated at pile foundation of node #2 and estimated onset time determined by 1 st and 2 nd AIC function at six different accelerometers. The onset times determined by the 1 st and 2 nd AIC function were marked with a black and red hollow dot. The amplitude of each signal was normalized with its peak amplitude for comparison. Figure 12: The accuracy improvement in source location by changing the number of sensors used for source localization: (**a**) average Euclidean distance error, (**b**) zoning accuracy. the signals generated at three different locations in the three-dimensional model scaled PRF: (1) raft top surface, (2) raft bottom surface, and (3) middle of a pile. As a result, the automatic single-stage AIC picker showed poor prediction accuracy for the sources in RT corner zones and PM central zones, with less than 90% accuracy, although it fairly reliably predicted the source locations for those in RT and RB central zones and RB and PM corner zones, with the accuracy higher than 90%. By contrast, the two-stage AIC picker clearly showed better prediction capability, with an increase in the overall accuracy from 88.3% to 95.3% compared to the single-stage AIC picker. This result proves that the two-stage AIC picker can be a useful tool for the automatic determination of arrival time to locate AE events. In addition, some signals showed low SNR because of the long propagation path. In such cases, the exclusion of some signals with low SNR out of all collected signals can improve the accuracy of source localization, such as the ones detected from the farthest sensors. For field implementation, the wave velocity of a structure of interest needs to be determined for accurate AE source location. The medium wave velocity used in the Simplex method has a significant influence on the accuracy in the source location. In our study, we found two cases: the RT and RB cases where the source is generated close to a raft versus the PM case where the source is generated in the middle of a pile. The use of P-wave velocity of the medium showed the best accuracy for the RT and RB cases, and using rod wave velocity resulted in good prediction accuracy for the PM case. Meanwhile, in PRF, the connection between the pile and the raft is the most prone to damage. Therefore, a source is most likely to occur close to the raft, though it is still uncertain and unknown at which location the crack or damage will be generated in foundations. In the field, it is suggested to measure the wave velocity, particularly the P-wave and rod wave velocities, on an exposed surface of the structure (e.g., concrete surface in a reinforced concrete structure). For example, the P-wave and S-wave velocities of reinforced concrete structures range \(\sim\)3600-4200 m/s and \(\sim\)2000-2500 m/s. We expect that the proposed approach exploiting the two-stage AIC picker to AE source localization can provide useful information on the damaged location in subsurface buried foundations that we cannot visually inspect. In addition, the onset time determination by using an automatic AIC picker can be challenging in the field due to the ambient noises, such as rain, hail, and wind with debris [36]. The signal filtering has to be preceded to minimize the noise effect. Additionally, due to the rapid attenuation of signals, coverage area and detectable signal distance can be limited, and these depend on the type and array of sensors and source localization method. Conceptualization, H.K., T.-M.O., J.-S.K., and T.-H.K. ; Methodology, Y.-M.K., H.K., T.-M.O., J.-S.K. and T.-H.K. ; formal analysis, Y.-M.K. ; investigation, Y.-M.K. and G.H. ; data curation, Y.-M.K. and G.H. ; writing--original draft preparation, Y.-M.K.