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 Gain process can be applied to any volume. It generates two result volumes:

  1. a volume with a scaling applied to the trace amplitudes
  2. a volume containing the scales applied (with suffix _scalars)

Use the *_scalars volume with a Volume Maths (Simple) process to:

  1. Apply the same gain to a different volume (multiply by scalars)
  2. Remove the gain from the scaled volume (divide by scalars)

When applied to gathers, lateral smoothing can be applied to the scalar calculation to avoid the impact of noise.

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

Create an Automatic Gain (AGC) process

Create a volume smoothing 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

Smooth a 2D/3D volume
  1. In the Details Panel, select a Volume.
  2. Select a Gain function:        
    • Smoothed absolute values
    • Smoothed root-squared values
    • Smoothed instantaneous amplitude
    • Windowed arithmetic mean
    • Windowed geometric mean
    • Windowed RMS
    • Windowed median
    • Windowed median mean
  3. [Optional] Enter in the Clip scalars.
  4. Enter the Window length (ms) and Window overlap (%).
  5. Lateral Smoothing: Smooth the calculated gain over a sliding window before applying. Applies to gathers and panelled data only.
    • Set this to 0 for stacks and other non-gather volumes. Lateral smoothing is not applicable to non-panelled data.
    • Radius (traces): The size of the smoothing window.
    • Trim (%): The percentage of outlying samples to discard from the smoothing window.
  6. Bulk scale: Set a scale to apply to the whole volume, on top of any data-dependent gain.

Note: To reverse the gain, use Volume Maths (Simple) process to divide the gained functions by the scalars.