Computation of Porosity of Tetrapods as Coastal Activity Place using Aerial and Drone Images

Abstract

In 2016 and 2019, the death rate from fall accidents at breakwater and tetrapod was 14.2% and 16.3% of whole coastal activity accidents, a higher proportion than other types of accidents. But there is no quantitative basis for assessing the risk of fallen at tetrapod. Thus this study introduces the method of calculating the porosity of tetrapod by image processing. Aerial image of the National Geographic Information Institute (NGII) and drone image was used. The target area was the tetrapod of the breakwater near Korea Maritime and Ocean University, Yeongdo-gu, Busan City, South Korea. We compared porosity results from Otsu threshold and Adaptive threshold methods. The result shows that Adaptive method gives about 2 times difference between aerial and drone image while Otsu method shows 3 times difference. It is revealed that the adaptive method can be applied with porosity measurement for tetrapod.