Operation - Normal Moveout Correction
As a Tullow Geophysicist I want Normal move-out correction. I want this because it is an operation I frequently perform.
Pre-Dev Notes: Normal Moveout correction approximately converts a pre-stack trace with non-zero offset into a zero-offset trace, flatten reflectors in CDP gathers (see figure below):
To perform a normal moveout correction, a table of RMS velocities is requires, although the internal velocity model is usually unknown.
RMS velocities for normal moveout can be estimated by fitting hy- perbolas to the non-moved out CDP gathers. This can be done by picking semblance peaks or by picking on constant velocity stacks.
Second Order Normal Moveout:
- classic correction for simulating a zero-offset trace from a non-zero offset trace
- assumes that seismic rays travel in a straight line from the source to a flat reflector in the subsurface and in another straight line to the receiver
- Equation: where t(o)= time at the original offset, i.e. the to from which samples are moved o = offset in m or ft t_0 = time at zero-offset, i.e. time to which samples are moved v_nmo = RMS velocity in m/s or ft/s
Reveal has 2 higher-order moveout corrections to account for non-hyperbolic moveout. Non-hyperbolic moveout can be caused by factors such as vertical velocity variations and anisotropy. Each type of higher-order move- out may be applied with or without applying normal moveout (NMO). The higher-order moveout corrections are:
- Fourth Order Moveout:
- Eta Moveout:
- Uses the anisotropy parameter η to estimate non-hyperbolic moveout --> the user must define a η table as well as a RMS velocity table
- without NMO
- where η = the unitless anisotropy parameter c = a constant between 1 and 1.2 (fixed to 1 in Reveal implementation ---> investigate)
- without NVO
Implementation Notes:
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System Test Changes:
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Bug Fixes:
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C++ API Changes:
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C API Changes:
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Success Criteria:
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CREATED ON - 31/03/2017