Off-line deep-towed seismic profiler

Abstract

A deep-towed seismic profiling system is being developed to obtain detailed subbottom structures in deep seas around island arcs like Japan. Features of the system are as follows: (1) Off-line towing: both a hydrophone streamer and a recording unit with power supply are equipped onto a deep-towed frame, whereas the sound source is towed at the surface. This means that the underwater system can be towed by wire without using any special cable. (2) No depth limitation: all electrical units except the streamer are kept in the pressure vessels (depth limit 10 000 m), and unlimited depth hydrophone elements are used for the streamer. Thus the system can be used in the deepest seas such as the Japan Trench, the Izu-Ogasawara Trench, etc. (3) Digital recording: an A/D converter with a floating point amplifier and magnetic bubble memory are used to obtain high quality and high volume data. This provides 120 db in dynamic range with 12 bit significance and 16 megabytes data space. The prototype of the system hardware is complete, and the control software for the system is under examination. Field tests have proved the operability and functional ability of the system.