Velocity Analysis: NMO button doesn't work

[kerimh...@gmail.com]

Hi,

I'm working on VA and in general everything is pretty clear.

But when clicking on NMO button it doesn't do anything (while Remove NMO is always disabled).

Also Hide Overlays doesn't waork either (even though I don't understand what exactly it should do).

How to apply NMO based on current velocity picking?

RedOS 7.3 (based on CentOS 7)

[Michael]

I just tried on the 2 builds sitting under the desk, and Apply NMO works for me.

They are: Sparky Linux, gcc 8, revision 262 and Open Mandriva, gcc 11, revision 270

I have one with Centos 7, but didn't try that, as it is very old revison, approximately 200.

[kerimh...@gmail.com]

Thank you for reply.

I just noticed that strange things start at Semblance calculation step using SVA module.

When I start Velocity Analisys using calculated semblances I can see that two headers are used: 7 and 8 (corresponds to xcoord and ycoord in vel ASCII file). 

Header 7 is my CMP number.

Header 8 shows some numbers that is hard to explain. The original SEGY file that was used to compute semblances has zeroed header 8. But semblance's header 8 has some non-zero values (I check this using CBYT and VA interactive tools). 

If I successfully pick velocities and save them to ASCII file then I can't use it in NMO module (not button in VA tool), I get error: gridcheck: X coordinate not unifor (it can't use bilinear interpolation on non rectangular grid).

Only if I manually edit velocity ASCII file and set header 8 (ycoord) to 0 everywhere then NMO module works fine.

Probably that is the reason why NMO button in VA doesn't work.

My data is 2D marine open source Viking Grabel line 12 data.

I attach workflows for NMO and Semblance computation

пятница, 21 октября 2022 г. в 15:36:13 UTC+3, Michael:

[kerimh...@gmail.com]

My theory was confirmed: if I set header 8 to 0 (using SETWORD module) then NMO button in VA tool works correctly.

Thus the question is why header 8 of semblance files (_svas.trc8 and _svat.trc8) is non zero even if original SEGY file's header 8 is zeroed?

пятница, 21 октября 2022 г. в 16:09:12 UTC+3, kerimh...@gmail.com:

[Michael]

I looked back when I processed that AVO12 line, and I had header 8 zero thoughout. Can you check all your jobs to see where you get the non-zero header?

The SVA process should not set header 8.

Unfortunately erratic header 8 will upset NMO, as the velocity file has to form a rectangular grid of parallel lines (or one 2D line). The line spacing can be unequal, but still rescticted to a rectangle.

The answer to your other questions about Hide Overlays button: if you go to Control Panel in va, you can display the previous and next velocity functions in different colours, They are the overlays.

If they are too close to the current picks, you can hide them.