Q Estimation

Description Estimates the effective Q from seismic traces.
Module(s) Image Gather Processing
Requirements Volume
Related Q Filter Q Conversion
Works with Stacks, Gathers, 2D, Velocity

The Q Estimation process estimates the effective Q from seismic traces. A trace of effective Q values is output for each input trace with the same time sampling as the input trace.

Create a Q Filter Process

  1. In the Control Panel, open the Process tab.
  2. At the tab header, click the blue "+" icon and select New Process.
  3. Double-click or search for Q Estimation.
  4. Type a name for the process and click OK.

Configuring the Q Estimation

Create Q Filter process
  1. Volume: The input seismic trace volume.
  2. Length of analysis window (ms): At each sample, the algorithm uses a window of data to determine the Q value. This is the size of that window (default: 300).
  3. Use high frequency cutoff: Select this to specify a high frequency cutoff in the Q estimation
    • High frequency cutoff at start of trace (%): This is the high frequency cutoff to use at the start of the trace. The Q estimation uses frequencies higher than the frequency at which the maximum amplitude occurs in the estimation analysis window. The cutoff percentage allows you to ignore frequencies more than the specified percentage from the maximum amplitude to Nyquist (e.g. if the maximum amplitude occurs at 50Hz and Nyquist is 250Hz, a cutoff of 60% will use frequencies between 50Hz and 170Hz).
    • High frequency cutoff at end of trace (%): This is the high frequency cutoff to use at the bottom of the trace. If you leave this blank the start of trace value will be used. Normally a significantly lower value is used for the end of the trace. The high frequency cutoff will be interpolated linearly between the start of trace and end of trace.
  4. Use threshold cutoff: Select this to specify a frequency cutoff based on an amplitude threshold.
    • Amplitude threshold cutoff (dB): The Q estimation uses frequencies higher than the frequency at which the maximum amplitude occurs in the estimation analysis window. The amplitude threshold cutoff limits the analysis to frequencies with amplitudes more than the specified value below the maximum amplitude. The cutoff occurs at the first frequency below threshold.
  5. Use low frequency cutoff: Select this to specify a low frequency cutoff in the Q estimation. If you use a low frequency cutoff, only frequency content above the cutoff will be used to estimate Q.
    • Low frequency cutoff at start of trace (Hz): This is the low frequency cutoff to use at the start of the trace.
    • Low frequency cutoff at end of trace (Hz): This is the low frequency cutoff to use at the bottom of the trace. If you leave this blank the start of trace value will be used. The low frequency cutoff will be interpolated linearly between the start of trace and end of trace.
  6. Half size of the trace window for spectrum smoothing: The spectra from the surrounding traces can be averaged to improve the spectrum used in the Q estimation. This parameter is the half width of the trace window used for creating the average spectrum. Use 0 for no averaging.
  7. Spectrum smoothing method: Select a method for smoothing the spectrum used for the Q estimation. This is applied to the spectrum after any averaging is performed.
    • Frequency smoothing radius (Hz): The smoothing radius for the spectra in the frequency direction (set to zero or leave blank for no smoothing in the frequency direction).
    • Time smoothing radius (ms): The smoothing radius for the spectra in the time direction (set to zero or leave blank for no smoothing in the time direction).
    • Size of hyperbolic smoothing corridors (HzSec): The hyperbolic smoothing occurs along hyperbolic corridors of constant time by frequency. The size of the corridors controls how many corridors are used. The bigger the value the more smoothing that occurs. A value around 5HzSec is a reasonable choice.
  8. Q estimation method: Select the estimation method to use - either Fourier Spectral Estimation or Maximum Entropy Method (default is Fourier Spectral Estimation)
  9. Output: Select the output from the process.
    • Effective Q
    • Peak frequency: The frequency where the peak amplitude occurs
    • Peak amplitude: The peak amplitude
    • Slope of ln (Amplitude squared) vs F: The slope used to estimate Q