Surface-consistent amplitude correction (SCAC) stage is one of the main steps in seismic time processing which is used for amplitude distortion correction caused by the near-surface irregularities or buried anomalies. The term surface-consistent implies that the time correction depends only on the surface location of the shot and receiver associated with the trace (Yilmaz, 2001). Surface consistent factors may be divided into source, receiver, offset, and subsurface components and these may be divided further into amplitude and phase (or time shift) factors. Correction of trace amplitudes using multiplication by a scale factor is similar to correction of phase distortions by a static shift, and both corrections enhance seismic data.

Current seismic data does not include such a high inconsistency in near surface interval, so there is no drama amplitude variations of sources and receivers. For example, West Siberia seismic data has a lot amplitude anomalies in accordance to the near surface influence due to the fact that there are a lot of marshes, complex low velocity layer, variations in topography and etc. Anyway let's have a look what we have on our seismic here.

Create a new workflow 0040_Surface_consistent_amplitude_correction:

And add all necessary modules, connect all input and output data (trace headers, SEG-Y handlers, ...):

1. Read seismic traces

2. Sort traces

3. Seismic loop (prepare seismic data for amplitude calculation)

4. Mute

5. SC Amplitude correction - Calculate

6. Seismic loop (apply amplitude corrections)

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  Do not forget to execute modules to display gathers, maps, data on Vista Windows.

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1) Read seismic traces. Load seismic data set 0030_Spherical_divergence.

2) Sort traces. Here we need to sort seismic traces for Seismic loop, not for SCAC (no sort is required for it). Therefore, add Sort traces module and set SOURCE_SP header for sorting as it is shown below:

3) Seismic loop  (prepare seismic data for amplitude calculation) . Connect trace headers vector (Input sorted headers) from the Sort traces module output and seismic (Input SEG-Y data handle) from Read seismic traces.

4) Mute module provides mute function creation and applying. Add all vista groups in your work area (screen). Draw a muting line on a source gather in the same manner like you did on the previous steps (geometry interaction).  Execute the Seismic loop module and look at the gather. Do not use location map, because we are going to create a mute function only for one gather, it would be enough. Look at the source gather, it is obvious that a high amplitude cones area has a great influence on surface consistent amplitude corrections (SCAC), so it has to be muted before SCAC calculations:

Parameters of Mute module: Type: Mute down, Taper window <ms>: 20:

Eventually, we have a mute function that we will use in SCAC. Save mute function by using Actions:

5) SC Amplitude correction - Calculate. This module is used to calculate operators for a surface consistent amplitude correction. Once calculated, the operators are applied using the SC Amplitude Correction – Apply module. Add this module to a workflow and put Mute and Band-pass filter inside Sub-sequence. Sub-sequence allows to use any procedures inside another procedure. In this case we apply mute function (Mute module) and constrain frequencies before SCAC calculation (Band-pass filter). Notice that it is safer to add a new module to the workflow, but do not use copy-paste option. Next, add a new Mute module and import mute picking  file (of course there is an option to get mute picking item from another Mute module, but we are not going to use this way). By Band-pass filter cut low and high frequencies 10-14--40-56 Hz. Execute SCAC and add all vista groups on the work area, change windows location and some other settings like color, trace headers for gathers that you would like to see, etc.

Define SCAC parameters:

Make some tests, change the following parameters and choose the most appropriate:

Desired amplitude level - level at which the data will be normalized to;

Domain for calculation - the domains in which the calculation will be completed: source, receiver, offset, bin;

Advance for Solver:

       Threshold Factor - amplitude constrain;

       Solver iterations - number of iterations run by the solver;

Maximum offset - maximum offset taken into account for the calculation;

Minimum offset - minimum offset taken into account for the calculation;

Offset step - size of offset pieces used in the calculation;

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  Every time you add a new module make all necessary connections for

input data (Data Items): trace headers vector, seismic handler, ...

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Execute the SCAC calculation. Use maps for source or receiver selection, check coefficients, convergence graph and if it necessary you may increase number of iteration or modify mute function and change SCAC parameters. Check results: look at gathers before and after SCAC.

Now you can use it in another workflow or connect corrections with the SC Amplitude correction - Apply as input AmplitudeRecoveryDataItem.

3) Seismic loop (apply amplitude corrections). Add Seismic loop and put SC Amplitude correction - Apply and Save seismic by gather inside. Get SCAC corrections from DB or from SC Amplitude correction - Calculate module, define SCAC apply parameters. Usually, SCAC correction is applied for sources and receivers to save AVO-effects, but in some cases Apply offset may be used. Also we can save SCAC corrections into the g-Platform's data base by using Save item module, but we are not going to do it in this workflow, it will be explained in Residual statics correction chapter.

Get SCAC correction from SC Amplitude correction - Calculate module as you already familiar how to get input data from other modules.

And define SCAC apply parameters:

Define a name for output data set 0040_SCAC1 in Save seismic by gather module. Execute Seismic loop for the entire data (press button from upper menu).

Next step >>> Noise attenuation before deconvolution.

      If you have any questions, please send an e-mail to: support@geomage.com    

Surface Consistent Amplitude Correction - Geomage g-Platform Tutorial - YouTube