Autocorrelation identifies periodicity in a signal, e.g. air gun bubble, reverberations and multiples. It is useful for detecting repeating periods within signals in the presence of noise.
At each lag value, the signal is correlated with a time-shifted copy of itself. The autocorrelation result is often normalised such that the value at zero lag is 1.
Create Autocorrelation process
- In the Control Panel, open the Process tab.
- Click the blue "+" icon and select New Process.
- Search and double-click Autocorrelation.
- Type a name for the process and click OK.
Define Autocorrelation settings
- Volume: Select the data to autocorrelate.
# of lags: The number of correlations (shifts by sample interval) to compute in the autocorrelogram.
- This includes the zero shift. e.g. "# of lags" = 3 gives an autocorrelogram with lags of 0, 1 and 2 samples).
- The number of lags determines the output trace length in samples.
- The zero lag will be at time 0.
- Normalise: Normalise the result so the zero lag autocorrelation is 1.
Trace windowing: Calculate the result for the full trace or a window
- Start of window: The start time/distance or horizon of the window.
- Window Length: The length of the input volume window.
- Entire Trace
- As a result of this process, a new volume is available in the Volume tab.
Example of autocorrelation
Nice example of a strong zero phase event at 0 ms with little noise in the data below. No coherent events below suggesting residual noise was removed.