meaning of redundancy

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Tingpingbing
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meaning of redundancy

Post by Tingpingbing »

What is the definition of data redundancy in seismic processing?

GuyM
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Re: meaning of redundancy

Post by GuyM »

When you have lot of seismic data containing the same information.

For example, modern marine seismic is often collected at a 2ms sample interval, and with a receiver group interval of 12.5m
This would allow for frequencies up to 250Hz (Nyquist) and a CMP bin spacing of 6.25m

Given the filtering effect of the Earth and the size of the Fresnel zone at the seabed, this is un-needed unless the work is in shallow water and targeting the near surface (first few hundred metres); we have many more samples and a much closer CMP interval than we need.

This is an example of data redundancy.

This is done for a reason. We can take the shot records and remove any high frequency dipping data that would be spatially aliased at a smaller sample interval and wider group interval via filtering (often in the Tau-P domain); we can then reduce the sample interval to 4ms and the group interval to 5m knowing that the spatially aliased data is removed, and so any steeply-dipping high frequency energy is genuine.

Similarly, stacking effectively stops having a signal:noise improvement about about 60 traces or so; more data in a CMP than this is effectively redundant when it comes to the stack. The advantage there is to have longer offsets and so much higher angles of incidence. These can be used to help extract information about the rock physics (via methods like AVO) and define better velocity fields and contain more complex arrivals for advanced imaging (Pre-stack depth migration)

GuyM
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Re: meaning of redundancy

Post by GuyM »

Oh - thank you for asking these questions!

I've stepped back from geophysics after >25 years in seismic and while I'm very happy with my new career direction, it is also nice that all of the stuff that I have learned over the last quarter of a century is not sitting in my head not helping anyone :-)

That said - do use the sources I have provided to look stuff up as well; I might not always be able to answer your questions!

Tingpingbing
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Re: meaning of redundancy

Post by Tingpingbing »

Thank you so much for all your help :D
You are really good at explaining and you make these different seismic definitions and
situations easier to understand.

I am on my 2nd year of studying geophysics. It is quite interesting.
Thank you for your help again. I will use your blog. :thumbup:

GuyM
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Re: meaning of redundancy

Post by GuyM »

Well - I have run a written and run a few seismic processing courses in my time ;-)

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