Kiyokazu Nishimura

Sea Floor Mapping using the Data of Forward Looking Sonar and Side-Scan Sonar around the Hydrothermal Sites, South Mariana Trough

Processed data of the mesotech 971 forward looking sonar was successfully plotted on a map and compared with side-scan-sonar (SSS) data and color image of original forward sea floor record. The accuracy of positions by LBL acoustic system is insufficient to process the sea-floor mapping. The accuracy and density of positions controls, in other saying, decides the quality of mapped seafloor images.

Development of off‐line, deep‐towed seismic profiler

A deep‐towed seismic reflection profiler has been developed by the Geological Survey of Japan. The aim of the system is to obtain detailed profiles of subbottom structures in the deep seas. The system consists of deep‐towed seismic recording packages with a deep‐sea hydrophone streamer, a shipboard data logging and processing system, and an acoustic navigation system for the deep‐towed packages. The packages are towed near the seafloor, and a sound source (an air gun) is towed near the sea surface. After the recovery of the packages on board, the seismic data in the package are transferred to the data logging and processing system through a high‐speed serial link. The system has the following features. (1) Off‐line towing: the hydrophone streamer and the recording packages are towed by an ordinary wire without a conducting cable. (2) No depth limitation: all electrical packages are kept in pressure‐proof housings (depth limit 10 000 m), and unlimited‐depth hydrophone elements are used for the streamer. (3...