We are nearly there.
Overnight we recovered another six ocean-bottom seismographs in between an Autosub recovery and redeployment today. That leaves us with just four to go for tonight’s shift.
So as the above image shows are shipping racks are almost full. Each OBS recovered so far has had its data downloaded and converted to a standard format, quality control checked and saved to storage. And that storage has been backed up twice to two other storage systems that we bought with us. Each of these storage systems will make it back to our lab by different routes as the data they hold is priceless and if lost, is lost forever as it would be very unlikely indeed that this experiment would be repeated.
So our final profile was called Profile R – we’ve already completed A-Q plus X and we never reuse names during the same experiment, whether profiles are actually acquired or not, everything gets a unique name, never to be repeated for the same experiment – and of the 14 instruments deployed on that profile the following 10 data sections (in order of deployment position N-S along that profile) show what we have achieved. We will now pass these, and the four to come for this profile and all the others for the grid survey to the scientists to analyse.
The smiley-looking part is where the OBS in one the seabed along the profile, and the smiles themselves are the signals travelling through the water direct to the instrument. We have recorded these to distances of something like Durham (our home base) to Edinburgh (for our readers in the UK), which is quite a long way really.
The signals travelling below the seabed plot across these figures almost flat as the plots are created in such a way as to emphasise signals travelling at 6 km/s, which is a velocity typical of rock that make up the crust. Signals travelling slower that that (say in sediment) dip towards the OBS, signals travelling faster (say in the mantle below the crust) dip away from the OBS, but here we have to be very careful as the severe seabed topography also makes the signals undulate up and down running across these reduced time plots as they are known.
And these instruments were sitting on the seabed lumps from the middle to the right hand side of this reflection image!
In addition to us packing up our OBS equipment, the other technical staff on the vessel are also packing up the seismic source and the multichannel streamer ready to be sea freighted home on arrival in Port of Spain.
Here are a few views of what the stern looks like now, and it is not dissimilar to how it looked when we loaded our containers in Southampton in December.
Stern is almost clear.
Airguns on a pallet ready to be racked into a container.
Multichannel streamer covered up to protect it from the sun – this will make its way back to the UK on the RRS James Cook itself.