Remember Boyle’s Law …..?

For the followers of this blog who are doing or did science at school or beyond – you may have wondered what the point of Boyle’s Law is? The memorable

P1V1 = P2V2

well here is one use.

Yesterday we completed the first phase of seismic surveying and we did a quick back of an envelope calculation as to how much air we had pumped into the water column at 2000 psi.

It was a very large number – 34.3 million cubic inches or 562 cubic metres.

Well today, in a spare moment between recoveries and redeployments, we’ve redone that calculation to see what that volume of air equates to at the atmospheric pressure we experience. This is where Boyle’s Law comes in.

Atmospheric pressure is approximately 14 psi. So substituting that, the compressed air pressure, and the volume of air at that pressure into the above equation gives a volume equivalent at atmospheric pressure of …….

80,385 cubic metres.

That is a box with sides 283 m long and 283 m high.

We have, of course, made some rather basic assumptions as part of this. One is that air is an ideal gas, that the air we have been generating contains no water vapour and so on. So, even if strictly just an approximation – its still an unimaginably huge volume of air.

So what else have we really been doing today?

Last night, by midnight, we had recovered the 4 instruments being retrieved from the seabed. We have downloaded their data and quality controlled it, and then reprogrammed them ready for redeployment with four more in addition today.

Here are some images of the recoveries from last night – it was quite windy!

And home safe and sound.

And this is a hot off the press look at the data – the blank part on the left hand side shows where we stopped firing to do some seismic array maintenance. The curving arrivals are signals travelling in the water from the seismic array to the instrument direct, and then the bounces off the seabed and then the sea surface back to the instrument on the seabed. The bits we are interested in are the signals travelling below the seabed and these are the ones travelling nearly horizontally across this plot at about 2s on the time (Y) axis. The ones on the far right hand side have travelled around 30 km sideways through the deepest parts of the Earth’s crust.

We have just completed the redeployment – 8 OBS deployed in less than 3 hours – OK they were only about 1.5 nm apart, but that’s still not bad going. The egret also took an interest and seemed to be doubly checking what we were doing as today’s banner image shows.

Here are some images of the final deployments for this research experiment.

And away this one goes for one final time.