Basic study on the estimation method of burrows on the seafloor using ultrasound

There is concern about the noise effect of offshore energy facilities. For example, noise generated during construction and operation of them may affect some aquatic species. Aquatic environmental measurements have been conducted to assess this effect. However, the effect under the seafloor remains unknown due to the lack of an efficient method for surveying a wide area. The marine environment is affected by the burrows formed by organisms living on the seafloor. Therefore, it is important to know the shape of the burrows of benthic organisms from the viewpoint of marine environmental conservation. In this study, we investigated a method for estimating the length and diameter of the burrow by transmitting broadband ultrasonic waves into the burrow and measuring, analyzing the echoes. The model experiment and the acoustic simulation using the finite-difference time-domain method were comparatively performed to verify the possibility of estimating the tube length and diameter. It was confirmed that the tube length was estimated with a relative error of about 3% for straight and U-shaped plastic tube models.