Ready, steady …..

….. go.

Here we are, back doing what we do best, our first large instrument deployment since before COVID arrived – 30 OBS – which is half of the entire fleet.

We are deploying all 30 once along one profile, and then they will be recovered and 15 will be redeployed along another profile.

Blog readers will know that we are working on a data acquisition in the eastern Pacific, jointly with another group from Germany.

To make the best use of time, given the challenges of working hours limits at sea, the two groups have divided the entire deployment up into batches, so that one can work while the other sleeps.

Our 30 instruments were divided into four groups: 9, 7, 9 and 5, with the other group’s instruments deployed in three groups in-between.

The first task of any deployment is to programme the dataloggers to tell them what needs to be done – what to record, for how long and how fast to sample the sensor output.

The next step is to build each instrument platform on top of its ballast weight, that makes it sink at a steady rate to the seabed.

Then the datalogger tube gets inserted and the cables to the sensors connected – a final in situ test of the acoustic release is also undertaken now that it is also connected to the cables that run to the burn wires that do exactly as their name suggests when a battery is connected to them – once burned the locking mechanism opens and the instrument platform starts its ascent to the sea surface, so these are rather critical systems.

Work on research vessels carries on 24 hours a day, seven days a week as the costs of keeping a vessel at sea is very large. So we see the sunset, and the sunrise.

Here goes the first.

And we carry on through the night.

And we are still going at sunrise.

Finally, the last of our 30 heads towards the seabed.

Once all the instrument platforms from both groups are deployed, then the sound source used for the sub-seabed imaging will be deployed behind the vessel, together with an alternative listening device that is towed at the sea surface – called a streamer – and these will be towed back along the entire survey profile firing a seismic shot at fixed distances.

It is the Earth science equivalent of CAT scanning that hospitals undertake to look inside the human body – both are looking for regions of different density: hard bits (bones), softer bits (muscles), very soft bits (fat) and even voids (lungs, stomach) – rocks are just the same!

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