Case Study: On a Deep-tow Piggy Back system, DAI-PACK - Pertinent information is coordinates, but tool is even more important -

Deep submergence vehicles bring us closer to the target we want to see in better resolution. It is difficult to obtain very detailed scale seafloor or sub-bottom structure profiling by a conventional surface-towed survey system, in which the horizontal spatial resolution in data obtained is poor because of the great distance between the sensors and the targets (seafloor/sub-bottom). To improve this horizontal resolution of the profiling, we have been developing and using deep-tow profiling systems for more than two decades at the Geological Survey of Japan, AIST. In our presentation we show our latest tool for the deep-sea mapping, named DAI-PACK (Deep-sea Acoustic Imaging Package) system, which has been tested and used in fields for more than four years now. It is not easy, however, to bring the tool deep and to maneuver and keep the towing altitude sufficiently close to the seafloor. To overcome this problem, we made the system work stand-alone and also made it portable in size and weight to be accommodated to ROVs (Remotely Operated Vehicle) or manned submersibles. We have chosen two sensors to be installed in the system, i.e. (1) deep-sea side-scan sonar and (2) deep-sea sub-bottom profiler. All components except sensors are packaged in an aluminum pressure sphere, which can be installed as a piggy back payload on many vehicles available today. From our recent experiments using the DAI-PACK on several vehicles, e.g. ROVs (the Hyper Dolphin in '03~'06, the ROPOS in '04, the Kaiko7000II in '06), and HOV (Shinkai6500 in '04, '05), we have learned several pros and cons regarding the use of the DSVs. We can discuss on the topics, such as (1) noise problem of the vehicles; ROVs were more noisy than Shinkai6500, (2) importance and need of good positioning of the vehicles;any DSVs we have used have not been installed a navigation system good enough to be collocated with the imagery data of the DAI-PACK, and (3) usefulness of sub-bottom profiling, based on real good/bad data we have collected. We haven't had a chance to use AUVs yet, but we can discuss about the advantage/disadvantage of using AUVs to some extent as well.