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Forum » Velocities » Import .grd or .xyz velocity file to nmo file

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Import .grd or .xyz velocity file to nmo file Link to this post

I am trying to import a velocity file from a wide-angle inversion into Claritas .nmo format. It is written as a GMT .grd grid. Is there an easy way of doing this?

I have found a convoluted way of doing this. I use "grd2xyz" followed by "sort" and "awk" to convert my .grd file to a single column ascii file, then I use Claritas' ascsegy to convert it to a segy file, see below for example script.

# /bin/bash
grd2xyz $1 \
| sort -n -k1,1 -k2,2 | awk '{print $3}' > temp.dat
ascsegy -ntraces 4001 -nsamps 1251 -dx 62.5 -sr 0.016 temp.dat $2
rm temp.dat

Here $1 is the input .grd file and $2 is the output segy file. Unfortunately this fails somewhere when I do it with a large 40000-cdp file. To make it work I have to subsample the velocity grid before the conversion. I then read the segy file with Claritas to fix some headers and in particular to define CDP number and then read the segy file with ISOVELS and save it to an Claritas .nmo file.


Re: Import .grd or .xyz velocity file to nmo file Link to this post


Sorry for the delay in answering your question, but it looks as though you have developed your own flow for reformatting and reading the GMT data.

You could look at the READGRID module to see if you can simplify your flow, as you should be able to read the GMT data and then go straight to SEGY and then into ISOVELS removing one of your steps that you currently have to undertake.


Andy Juniper

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