R/V Falkor slows down to 2 knots. At this speed, the gentle swell that has accompanied the expedition from the start cradles the ship. At the aft of the vessel, everyone involved in the deployment of the seismic reflection gear is wearing safety gear, while at the bridge the officers monitor the procedure and keep a steady course.
First things first
A 1200 meter streamer, filled with 96 hydrophone clusters – called channels – rests on a winch. The streamer loads in first, and the whole deployment will take about an hour. “It’s a pretty straightforward process” says Anthony Deebank, from the SALT –Sea and Land Technology – team.
The tail buoy is attached to the streamer – its primary function is to drag the heavy equipment as it is released into the water. Once the streamer is up and running, the GPS system installed on the buoy will provide information on the streamer’s position, which will be later used when the data collected is being processed.
Every 300 meters orange wings slide away, hooked to the streamer. “Those are the birds,” explains Deebank, while attaching weights onto the equipment at designated positions. “They help to stabilize the streamer.” The combination of the birds and the weights will help keep the streamer at roughly 4.5 meters of depth.
Think of everything
The scientists request that the streamer floats at a specific depth. The depth will determine in which segments of the frequencies recorded they will be likely to find “ghosts,” or holes in the data.
Water salinity and temperature play a role. If the water is cold, the equipment will tend to float more. Likewise, the greater the salinity, the greater the buoyancy. By using a series of charts, the SALT team determines just how much weight must be attached to the gear.
Nothing is left to chance, and now that the whole length of the streamer is being trawled by R/V Falkor, it is time to deploy the main attraction.
Seismic source
An air-gun will create sound waves that travel to the bottom of the ocean and return to the surface after bouncing on different layers of the subfloor.
Deploying the seismic source takes an extra half-an-hour. NowR/V Falkor increases its speed to 4 knots, and keeps it constant. The air-gun creates waves every 25 meters, and once those waves are picked up by the hydrophones on the streamer, images begin to appear on the screens of the Visual Matrix.
The seismic reflection equipment will remain afloat, working day and night with only a few brief respites, whenever the constant vibration demands some swiftly served maintenance.
