The early hours of this morning saw the last four ocean-bottom seismographs recovered from the seabed.
And almost as soon as the last one was aboard, the lab stripping and packing process started.
The image above shows one of our team members communicating with the last instrument as the vessel moves alongside to pluck it from the water.
So to complete the array of data sections from Profile R – here are the last four from the instruments we recovered this morning.
We are now just doing the last bits of bathymetry surveying before heading to Port of Spain in Trinidad and Tobago.
So where did we get to, and how many circles, squares, triangles, shimmies. curves, turns and bends did we complete? Here is the track to the last cruise activity – the Autosub recovery.
So the final score – in terms of OBS activities:
OBS deployments – 75 – of which 7 were tests of our new sensor systems and their gimbals
Number of recorded shots lying along profiles to be analysed – 7237
Line kilometres shot and recorded – 1085 km
Average rise rate from the seabed of our OBSs – 47 m/min
Average rise time from the seabed – 68 mins
Average time to catch one once surface and get it on deck – 15 mins
How do we manage to catch these instruments so quickly you ask?
Well, we note the position of each we recover from the start and a pattern starts to emerge very quickly as this map shows, and it allows us to predict in which direction they are likely to drift as they ascend and position the vessel so that each will come up on the bow, and with the vessel sitting downwind which makes it easy to manoeuver for a quick recovery. During this experiment the instruments basically went west by 200-300m from where we deployed them.
The red dots in the map show where we deployed each OBS, and the green dots where we plucked them from the water. The pattern is clear if you record and plot it for each as you go! These are all 75 deployments, and as you can also see the seabed topography is far from flat.
So, we are currently bathymetry surveying to the south of the above map, and this data is cleaned and processed as it is acquired using a computer that is part of the vessel’s equipment. Watchkeepers from the science party have been doing the task as we go along as the data volume will get very large by the end and then it becomes a very daunting job to deal with once back at their lab. The white dots on this picture of a bathymetry swathe, are the bits that need editting – or cleaning – out.
So – now all that’s left is to pack, and here is how we are getting on – compare these photos with those from earlier blogs. It all ends up in a box somewhere, and some of the boxes get very full and very heavy.
When we get to port all of the boxes get stacked into 20′ sea freight shipping containers and sent back to our lab in the UK. That is the very last job before we sign-off until our next adventure.
One of many boxes we have!