Development of off‐line, deep‐towed seismic profiler

Abstract

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) Digital recording and nonvolatile, solid‐state memories: an A/D converter with a floating‐point amplifier is used. Digitized seismic data are recorded in 16‐megabyte magnetic bubble memories. Field tests of the system were successfully carried out. Some preliminary profiles of deep‐towed digital seismic data were obtained.