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Repairs, Seismics (lesson 2) and Naughty Nigel.

This is the magnetometer. It had to be taken out of the water so that the airguns could be repaired. The magnetometer measures the magnetism of the sea floor.

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The airguns being lifted in for repair.

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Ian and Jason repairing the airgus.20160202_144529-480x853

 

 

Collecting Seismic Data:

reflection points

PROBLEM: For each shot gather (one shot, lots of receivers) the point on the geological boundary where the reflection occurs varies with distance between the shot and the receivers. If there is any lateral variation (e.g. folding, dip etc.) then image would smear out badly.

SOLUTION: Using data from many different shot gathers (each with lots of receiver traces) re-sort the traces so they don’t have a common shot, but so they have a common mid point = CMP gathers – approximates common reflection point

  • each trace is  a shot-receiver pair with a common mid point (e.g. shots all on one side, receivers all on the other). See below:

 

CWP

  • a – Single ray path of energy.
  • b – Each shot samples several locations
  • c- Some rays are not needed by scientists and are discarded
  • d- The acoustic records arranged not by a common shot but by a common mid point. CMP. This will give a trace line of zero at the CMP. Scientists can work out data from there.
  • A trace is vertical black line as seen in the diagram below.

What happens next?

trace

If you have any questions please do ask them via the comments in the blog. Somehow Nigel has found his way on to my diagram??? – I blame Matt!

Naughty Nigel:

Nigel took my new RRS James Cook coffee cup and asked for fish as ransom.

 

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Contrary to government policy I paid my ransom (thanks to Darren and Chris in the galley) and my cup was returned. As you can see I have put down warning to Nigel to prevent such occurrences from re occurring.

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Cheers

Angela

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