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Common Issues & FAQ

Forum » Common Issues & FAQ » OFFSET and COORD_SCALE (or NMO/LMO/Mutes not working!)

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Author Topic: OFFSET and COORD_SCALE (or NMO/LMO/Mutes not working!) 2619 Views

OFFSET and COORD_SCALE (or NMO/LMO/Mutes not working!) Link to this post

GLOBE Claritas uses a SEGY-like data structure, with IEEE samples and integer trace headers.
Extensions to this are managed as hidden files - history, additional headers (over the 240-bytes) and so on.

While extended headers can be any format, the basic headers are all stored as integer values, as with SEGY.

Unlike standard SEGY, we apply the coordinate scalar to the OFFSET value; this allows you to have decimetre (or decifeet) precision in your offset values.

If NMO, LMO or a mute file is being applied strangely - or seems not to be applied at all - it is worth checking that the coordinate scalar (COORD_SCALE) matches the offset (OFFSET) values in the trace header.

A -10 for COORD_SCALE is the default value for any geometry file created by GLOBE Claritas, and implies decimetres (or decifeet).

Care should be taken when modifying OFFSET or COORD_SCALE manually - the SETSCALES module updates both headers (as well as any X,Y values) but SETHEADER and HDRMATH do not.

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