Rapid Digital Seismic Surveys
The current high-speed seismic data acquisition system is no longer in use. Ifremer has chosen a system based on SERCEL digital technology to replace it, which is used with the SMT and HR acquisition systems.
This tool is deployed on the institute's various deep-sea vessels.
This system includes seismic streamers, seismic acquisition electronics (SERCEL SN408 laboratory), two immersion sensors and on-board quality control/processing tools.
Main technical features:
- streamers : 12.5 m traces, 16 hydrophones per trace ; 4 traces per 50 m active element; 1 x 150m ballasted head cable; 1 streamer reel with capacity for 300m of active sections,
- SN408 HR acquisition laboratory: 24 bits, sampling from 0.25 to 4 ms, up to 12 auxiliary traces, not high voltage, real-time acquisition and quality control software,
- offset for the implementation and quality control screens in the scientific command room
- pressure gauges: 2 pressure gaugues at the top and bottom of the active section and accurate shot dating,
- all acquisition electronics centralised in a 10 foot container;
- interface with the ship's instruments. DGPS positioning, gyrocompass, probe.
- GI 105/105 and 45/45 type guns with special streamlining (traction speed of 10 knots)
- Immersed in 6 metres of water at a surface speed of 10 knots
- 140 bars' pressure
- 2 x 300 m3/h compressors or 2 x 10 foot containers containers
Examples of deployment in different oceanographic vessels:
- RV Le Suroît, 1 streamer with 24 traces ; 2 GI sources, 1 'acquisition electronics' container ; 2 compressor containers and 1 workshop container
- RV Thalassa, 1 streamer with 24 traces ; 2 GI sources ; 1 'acquisition electronics' container; 1 compressor container and 1 workshop container
- Vessel speed 8-10 knots
- Optimal immersion 6-7 m
- Frequency: 50-55 Hz
- Vertical resolution 5m ; horizontal resolution 25m
- Shooting rate 5 to 10 seconds
- Data volume 4-10 GB per 24 hours
- Ground penetration: several hundred metres depending on the sediment type, source type, water depth, acquisition geometry, image processing quality, …
- Simultaneous acquisitions possible: SMF bathymetry, sediment sounder