Geopsy: H/V and Spectrum Toolboxes: Output Tab

Output tab where the user can fix the parameters to display and save the results

Through this tab, the user is able to fix the parameters to display and save the results.

This tab is divided in three sections

• Frequency sampling section: where the user can fix the parameters on frequency limits and more

• Appearance section: where the user can fix automatic output graphics appearance parameters

• Output section: where the user can fix where to save data

Frequency sampling section

Frequency sampling where the user can fix the parameters on frequency limits and more

In this section, it is described how it is possible to fix the upper and lower limits (in the frequency domain) for computing. This part is strongly linked to the properties of the Fourier transform.

• The lower limit should be fixed in two different ways :
  • The first possibility is to fix the lower frequency limit equal to the natural frequency of your sensor.
  • From SESAME output , the other possibility is to define the lower frequency limit from the window length taking into account the following formula ${\frac {10}{w_{l}}}>f_{seismometer}$. Where ${w_{l}}$ is the window length and $f_{seismometer}$ the natural frequency of your sensor.
    Example 1, if the windows have been fixed to exactly 25 seconds, the lower frequency limit is 0.4 Hz.
    Example 2, if the natural frequency of the used sensor is 0.2 Hz, the lower frequency limit is 0.2 Hz (giving a maximum window length of 50 s.).
    Example 3, if the natural frequency of the used sensor is 0.2 Hz and the window length has been fixed to 25 s., the higher frequency should be used. In this case: 0.4 sec.
    
    Of course, it is always possible to pass over this limitation by computing and viewing at lower frequency, but in this case, the user shoud keep in mind that the data below the "theorical" limit are useless. Moreover, in the graphics of H/V or Spectrum a red dashed area will appear in the frequencies below the ${\frac {10}{w_{l}}}$ frequency, as a reminder.

• The maximum upper limit is fixed by the Nyquist frequency, which corresponds to the half of the digitization frequency sampling. If the signal has a 100 Hz sampling frequency, the Nyquist frequency will be 50 Hz.
  Above Nyquist frequency, due to the Fourier transform in itself, no data are available. So there is no need to go above the Nyquist frequency.
  Below Nyquist frequency, there is no lower limit to the upper limit, except the lower limit frequency.
  In general, the upper limit is fixed in-between a 10-50 Hz frequency range.
• Two options have to be fixed
  • Step: option to define how the sampling of the Fourier transform (along the given limits, lower limit and upper limit) will be distributed. A drop box proposes two possibilities for the sampling:
    • Lin, for linear sampling. In this case, the samples are linearely distributed in the frequency domain.
    • Log, for logarithmic sampling. In this case, the samples are logarithmically distributed in the frequency domain.
  • Number of Samples. This spin box allows the user to define the number of samples needed to process the Fourier transform.

Appearance section

automatic output graphics appearance parameters

Output section

where to save data