Due to the recent increasing demand for construction of both large harbours and ocean developments, there is a great necessity to construct large ocean structures at 20 to 50m below the water surface. In order to do this both safely and economiacally, more accurate in formation on engineering properties of subsoils will be required.
　At present, however, soil investigation methods suitable for such depths are not available. Using standard methods designed for shallow water can lead to inaccourate and unreliable results.