Automatic Gain (AGC)

 Description Apply data-dependent scaling to a volume. Module(s) Explorationist, Gather Attributes Requirements Volume Related Gain Volume Maths (Simple) Works with 2D, Stacks, Gathers

The Automatic Gain (AGC) process creates data-dependent gain functions to balance amplitudes throughout the volume.

Amplitude values are computed from the trace data using a metric the user selects, and scalars are calculated based on the inverse of these amplitudes. The process generates two result volumes:

• A volume with a scaling applied to the trace amplitudes (scaled data)
• A volume containing the scales applied (scalars with *_scalars suffix)

When applied to gathers, lateral smoothing can be applied to the scalar calculation to avoid the impact of noise. Scaled data is the product of the scalars with the input data. To reverse the gain, use the Volume Maths (Simple) process to divide the scaled data by the scalars.

Note: For data-independent gain functions, use the Gain process instead.

Create an Automatic Gain (AGC) process

1. In the Control Panel, open the Process tab.
2. At the tab header, click the Add icon, and select New Process.
3. Scroll down, and double-click Automatic Gain (AGC).
4. Type a name for the process, and click OK.

Configuring the AGC Process

1. In the Details Panel, select a Volume.
2. Select a Gain function.

The amplitudes for some options are calculated within windows. The windowed gain functions are:

• Windowed arithmetic mean
• Windowed geometric mean
• Windowed RMS
• Windowed median
• Windowed median mean

The other AGC functions are not windowed. Instead, they use a smoothing radius. These whole trace gain functions are:

• Smoothed absolute values
• Smoothed root-squared values
• Smoothed instantaneous amplitude
1. [Optional] Enter in the Clip scalars.
2. Enter the Window length (ms) and Window overlap (%) for windowed gain functions, and Lateral Smoothing for whole trace functions.

Note: Lateral smoothing smooths the calculated gain over a sliding window before applying. Lateral smoothing only applies to gathers and panelled data. Set this to 0 for stacks and other non-gather volumes. Lateral smoothing is not applicable to non-panelled data.

1. Lateral smoothing radius (traces): Number of traces considered on each side of the trace being smoothed.
2. Lateral smoothing trim (%): Set the highest and lowest lateral smoothing trim percentage of the scalars within each lateral window are discarded before calculating the mean of the remainder.
3. Bulk scale: Set a scale to apply to the whole volume, on top of any data-dependent gain.