Combining Bathymetric Mapping with Side Scan Sonar
Yoshiaki Igarashi
Metal Mining Agency of Japan, Japan.
Toshiaki Ueki
Sanyo Techno Marine, INC. Japan
Introduction
It is critically important to map the detailed seafloor topography in order to evaluate the potential of manganese nodule resources because of presence of obstacles on the seafloor such as cliffs and hills considerably reduces minable areas. Two systems have been widely used for detailed topographic surveys: Multi Beam Echo Sounder (MBES) can provide a bathymetric map twice as wide as the water depth; on the other hand, side Scan Sonar (SSS) can provide a high-resolution acoustic image of the seafloor. We present 3-D views generated by combining the Multi beam Echo Sounder map with the Side Scan Sonar imagery.
Survey of Manganese Module
Since 1963, the Metal Mining Agency of Japan (MMAJ) has always strived towards the promotion of metal mining industries in Japan and throughout the world in the field of mineral exploration, mine developments, technological R&D, prevention of mining related polluted and much more.
In 1975, MMAJ commenced exploration activities for manganese modules in the Clarion Clipperton Fracture Zone in the Pacific Ocean at the request of the ministry of international trade and Industry (MIT). The activities were reinforced with the launch of the research vessel. Hakurei-muru No. 2 in 1980, which is exclusively designed for exploration of deep-sea mineral resources.
MMAJ has been involved in not only exploration of manganese nodules but also development of undersea technologies, ore processing, post-processing of data and environmental impact research. In addition, MMAJ has explored polymetallic sulfide deposits in the high seas of the East Pacific Rise and cobalt – rich manganese crusts in the north western part of the Pacific Ocean.
Here, we present our R/V Hakurei – muru No. 2 and MMAJ’s various activities relating to deep – sea mineral resources.
From 1989 to 1991, detailed surveys were concentrated in the western region of the Japanese Application areas in the Pacific Ocean using R/V Hakurei-maru No. 2. Also, locations of the survey lines and points are summarized in fig. 1.
Side scan sonar was towed totally 280 nautical miles long at the speed of 1 or 2 knots, while the towfish was 80 meters off the bottom. The side scan sonar image shows cliffs on the seafloor as gray stain in fig. 2.
The topography of the seafloor was mapped by Multi Narrow Beam Echo Sounder, while the interval of each ship’s track is 2 -3 miles so that ten-meter contoured map can be made (fig. 3).
Fig 1. SSS towfish, CDC vehicle and MFES track lines
Fig 2. SSSmosaics. SSS image shows obstcles as "gray stains".
