Pop goes the …..

….. seismic source.

Yesterday we completed the deployment of all seabed instruments along profile and, today, it was time to deploy the seismic source that creates the signals that travel through the rocks in the sub-seabed and that the instruments will ultimately record when they arrive back at the surface.

First the seismic streamer which contains numerous pressure sensors called hydrophones.

This streamer is 6 km long and has a hydrophone every 12.5m – that’s 480 individual sensing channels.

The streamer is split over two winch drums – one in front of the other.

Back drum is still full, front drum is empty – so 3000m deployed.

The first go at any new activity during a research cruise always draws a crowd, who watch, in this case, the streamer disappear over the stern and into the water.

Once all 6000m of streamer are deployed, next uts the seismic source – the airguns – of which thee are 13.

And finally, when all the equipment is deployed, the airguns are fired, starting one at a time, and adding a new one in every 20 mins of so until they all all firing.

If you look carefully you can see the bubbles of air rising until they breach the surface.

But not everything has gone swimmingly – and perhaps that isn’t the right phrase – one of our team returned to their cabin to find it flooded by a burst fresh water pipe.

Fortunately, nothing was damaged or waterlogged and our team mate moved to another cabin. The ship’s engineers will have had to paddle to fix this.

So, we will be shooting air bubbles every minute for 6 days now – that’s almost 9000 shots, listened to by 45 instruments on the seabed, each with four sensors, so that is 1,620,000 separate measurements by technology on the seabed.

What about the towed streamer?

That makes 480 measurements for each shot, so 4,320,000 separate measurements – just over 2.5 times as many.

Either way, that is a lot of seismic arrivals to analyse to get a model of the subsurface.

And we have received an update from the team at home – it is a balmy -9.5C!

And isn’t a Haw frost amazing – perhaps not in the Pacific!

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