Editing SU source code (nmo.c)

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nestorkid
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Editing SU source code (nmo.c)

Post by nestorkid »

Hi, I am working on editing the sunmo.c file source code in SU for elliptical moveout but have not made any progress with this.
Reason being that I could not get hold of all the routines for the sunmo.c source code. Does anyone know how best to go about editing the SU source code? Regards

showman
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Re: Editing SU source code (nmo.c)

Post by showman »

Follow these instructions to get all the source code and install:

https://github.com/JohnWStockwellJr/Sei ... l-on-Linux

It's a Makefile based build. All you have to do is edit the source code how you please then re-make and install.

nestorkid
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Re: Editing SU source code (nmo.c)

Post by nestorkid »

Thanks for the reply.
I already have the SU installed and the sunmo.c source code copied out. The challenge I am having is not being able to locate some important subroutines I think I need to access for what I need to do. I may be wrong, I am not so sure being new to programming.
I have been to github.com severally but could not get good direction there.

showman
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Re: Editing SU source code (nmo.c)

Post by showman »

What are the missing subroutines?

nestorkid
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Re: Editing SU source code (nmo.c)

Post by nestorkid »

intvv (not sure what the full meaning is) routine has the NMO equation I wish to edit and replace with tau-p NMO application but I can't seem to find it.

This information was given to me by John Stockwell, who mentions that the NMO equation is implicit in the intvv routine which the sunmo.c calls but this routine I have not found.

Finding the routine would help me understand how the nmo equation is applied to the data set.

showman
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Re: Editing SU source code (nmo.c)

Post by showman »

Which version of the source are you using. I'm looking at version 44 and there is no reference to intvv. The NMO equation is in the main body of sunmo.c. It's the line that says: ttn[it] = sqrt (tn*tn + tsq).

nestorkid
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Re: Editing SU source code (nmo.c)

Post by nestorkid »

I also use version 44R14. I have seen the line you referred to.
I was actually looking at the line that says /*do nmo via 8point sinc interpolation*/
ints8r(nt,1.0,......; which was where I expected to see it.

Thanks for pointing that out. Guess the ints8r routine makes use of the output of that line.

showman
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Re: Editing SU source code (nmo.c)

Post by showman »

Yes the NMO equation is the "forward" equation. It tells you what time you need to get for a given t0. This t0 comes from your output trace and is regularly sampled at dt. ints8r interpolates an amplitude between samples which is where your forward mapped NMO times will inevitably be.

bman
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Re: Editing SU source code (nmo.c)

Post by bman »

Hi, I am very new to seisunix so would appreciate some help. I am trying to combine four seg-y files into one continuous seg-y file. Although there are no gaps between the seismic lines (i.e. all 4 lines should join up to make a continous line) each has different parameters (headers, sample numbers etc.). My overall aim is to create a continuous seismic line in seg-y format that can be loaded into Petrel for interpretation.

So far, I have managed to convert each of the four lines from seg-y into the su format using segyread. I then used the following to make one file out of the 4 lines:

cat seismic_line-1.su seismic_line-2.su seismic_line-3.su seismic_line-4.su > composite.su

From what I understand, the next stage should be to create a header for the composite.su file however I receive the following error when I do the following:

segyhdrs < composite.su > composite_header.su
segyhdrs: fgettr.c: on trace #396, number of samples in header (1076) differs from number on first trace (1001)

If anyone can help I will be very greatful. Alternatively if anyone has a better suggestion of how to do this please can you also share.

Thanks,

Bman

nestorkid
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Re: Editing SU source code (nmo.c)

Post by nestorkid »

bman wrote:
Mon Dec 09, 2019 4:27 pm
Hi, I am very new to seisunix so would appreciate some help. I am trying to combine four seg-y files into one continuous seg-y file. Although there are no gaps between the seismic lines (i.e. all 4 lines should join up to make a continous line) each has different parameters (headers, sample numbers etc.). My overall aim is to create a continuous seismic line in seg-y format that can be loaded into Petrel for interpretation.

So far, I have managed to convert each of the four lines from seg-y into the su format using segyread. I then used the following to make one file out of the 4 lines:

cat seismic_line-1.su seismic_line-2.su seismic_line-3.su seismic_line-4.su > composite.su

Hi bman,

I have not done concatenation of segy files in su. However, I am convinced you cannot use cat to achieve what you want, which is putting the segy files together, except if this is how su achieves it.
I will suggest looking at the man page of segyread using "man segyread" to see if you can read more than one segy file into a single su file. If this is possible then you can read the headers of all the files to know if the headers are same which I suppose it might be. If it is not it implies you will need to understand how they differ, this will help you understand how to go about putting the segys together.

I hope this helps

Regards,

Nestorkid

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