Linear Move Out (LMO) - constant-velocity linear time shift to flatten linear seismic events such as direct waves and refractions.

Theory

Linear Moveout (LMO) is a correction that removes or applies a linear time shift proportional to offset, using a constant reference velocity. Unlike NMO, LMO assumes a straight-line (linear) relationship between travel time and offset and does not account for hyperbolic moveout.

LMO is primarily a diagnostic and preparatory correction, not a final moveout correction.

When do we use LMO?

• Before velocity analysis, to approximately align linear events
• For refraction analysis and first-break alignment
• To flatten direct waves, head waves, and linear noise
• As a preconditioning step before NMO or FK filtering

Why do we use LMO?

• Simple and computationally efficient
• Enhances coherence of linear events
• Helps separate linear noise from hyperbolic reflections
• Provides a constant-velocity reference for QC and analysis

Calculation of LMO correction is made according to following formula:

T = \frac{x}{v(N)}

Where

T -  Time after LMO correction or static correction in ms

x - offset

v(N) - velocity at any given N

N - value, normally with distance as its unit of measure

Input data

Input DataItem

Input gather

provide the input gather for LMO correction. Connect/reference to Output gather.

LMO function

in case the LMO option from the parameters is LMO function, then the user should provide the LMO function as an input.

Parameters

LMO { V const, LMO function } - selects the LMO type from the drop down menu. Select whether LMO is applied using a single constant velocity or a time-dependent LMO velocity function.

V const -  applies LMO using one constant reference velocity for all times and offsets.

LMO function - uses a time-variant velocity function to apply LMO correction.

LMO direction { Forward, Reverse } - select from the drop down menu, whether LMO correction should be applied or removed. By default, Forward.

Forward - applies linear moveout correction

Reverse - removes a previously applied linear moveout correction.

T0 - reference zero-offset time used as the baseline for LMO shifting. By default, 0 ms.

Reference velocity - constant velocity used to compute linear time shifts with offset. By default, 2000 m/s

Settings

Auto-connection

By default, TRUE(Checked).It will automatically connects to the next module. To avoid auto-connect, the user should uncheck this option.

Bad data values option { Fix, Notify, Continue }

Bad value fix - This is applicable whenever there is a bad value or NaN (Not a Number) in the data. By default, Notify. While testing, it is good to opt as Notify option. Once we understand the root cause of it, the user can either choose the option Fix or Continue. In this way, the job won't stop/fail during the production.

Notify

It will notify the issue if there are any bad values or NaN. This will halt the workflow execution.

Fix

It will fix the bad values and continue executing the workflow.

Continue

This option will continue the execution of the workflow however if there are any bad values or NaN, it won't fix it.

Number of threads

One less than total no of nodes/threads to execute a job in multi-thread mode. Limit number of threads on main machine.

Skip

By default, FALSE(Unchecked). This option helps to bypass the module from the workflow.

Output data

Output DataItem

Output gather

outputs LMO corrected gather (forward/reverse) as an output as well as a vista item.

Information

There is no information available for this module.

Examples

In this example workflow, we are applying forward LMO first, followed by LNA to attenuate some of the linear noise. Later, we use reverse LMO to bring back the input gather to it's original position.

Adjust the parameters as per the input data requirements.

Apply Linear Noise Attenuation (LNA) with an appropriate parameters to attenuate the linear noise.

Finally reverse the LMO correction by changing the mode.

Actions

There are no action items available for this module. so the user can ignore it.

Video lesson

YouTube video lesson, click here to open [VIDEO IN PROCESS...]

Related articles

Yilmaz. O., 1987, Seismic data processing: Society of Exploration Geophysicist

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