Improvement of robustness in ultrasonic attenuation spectroscopy for detecting internal insect damage in wood member of cultural heritage

Insect damage is one of the most serious problems in conservation of wooden cultural heritage buildings. Because this damage is quite small in a cross section, it is difficult to detect by conventional ultrasonic techniques. In the previous study, ultrasonic attenuation spectroscopy showed a feasibility to detect this small defect. But to apply this method to real inspection, the robustness needs to be improved. For improving the robustness, this study focused on inconsistency of ultrasonic spectrum measurement. To minimize the inconsistency, Spectra-averaging pretreatment was attempted. Even though this pretreatment would provide the better robustness, it can also make a negative effect on the accuracy in the detection of small damage. Therefore, the influence of the pretreatment on the prediction was investigated in this study. By ultrasonic attenuation spectroscopy, the number of drill hole was predicted. When comparing the accuracy in prediction using the pretreated spectra from the prediction without the pretreatment, the accuracy was not lower than that without the pretreatment or the previous study. Therefore, it was concluded that the Spectra-averaging pretreatment does not make a negative effect on the prediction.