Introduction

One of the major differences between underwater and land observations is that the spatial information of depth must be considered in underwater observations. For example, in investigating the distribution of species in the ocean, organisms that inhabit the ocean are entirely different depending on depth, even if they are located horizontally in the same location. In other words, underwater observation is the observation of a huge three-dimensional space in the ocean. Furthermore, the direct observation of a location in the ocean is complicated due to problems such as the limited distance light can reach in the ocean and water pressure. Therefore, efficient underwater observation requires a tool that remotely enables a wide range of observations.

Sound waves are transmitted through liquids and solids better than radio and light waves. Therefore, sound waves are used as a superior tool for wide-range observations. In our laboratory, we are working on sound waves in underwater observation, particularly with the main theme of estimating marine living resources. Our research aims to accurately estimate the number of resources of various organisms, ranging from fish to zooplankton, that sound waves can observe.