Difference between revisions of "Geopsy: H/V and Spectrum Toolboxes: Output Tab"
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** From SESAME output <ref>Guidelines for the implementation of the H/V spectral ratio technique on ambient vibrations measurements, processing and interpretation, [http://SESAME-FP5.obs.ujf-grenoble.fr], 62 pages, April 2005</ref>, the other possibility is to define the lower frequency limit from the window length taking into account the following formula <math>\frac{10}{w_l}>f_{seismometer}</math>. Where <math>{w_l}</math> is the window length and <math>f_{seismometer}</math> the natural frequency of your sensor.<br/>Example 1, if the windows have been fixed to exactly 25 seconds, the lower frequency limit is 0.4 Hz.<br/>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.).<br/>Example 3, if the natural frequency of the used sensor is 0.2 Hz and the [[Geopsy:_Window_Length|window length]] has been fixed to 25 s., the higher frequency should be used. In this case: 0.4 sec.<br/><br/> 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_spectral_ratio|H/V]] or [[Spectral_amplitudes|Spectrum]] a red dashed area will appear in the frequencies below the <math>\frac{10}{w_l}</math> frequency, as a reminder. | ** From SESAME output <ref>Guidelines for the implementation of the H/V spectral ratio technique on ambient vibrations measurements, processing and interpretation, [http://SESAME-FP5.obs.ujf-grenoble.fr], 62 pages, April 2005</ref>, the other possibility is to define the lower frequency limit from the window length taking into account the following formula <math>\frac{10}{w_l}>f_{seismometer}</math>. Where <math>{w_l}</math> is the window length and <math>f_{seismometer}</math> the natural frequency of your sensor.<br/>Example 1, if the windows have been fixed to exactly 25 seconds, the lower frequency limit is 0.4 Hz.<br/>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.).<br/>Example 3, if the natural frequency of the used sensor is 0.2 Hz and the [[Geopsy:_Window_Length|window length]] has been fixed to 25 s., the higher frequency should be used. In this case: 0.4 sec.<br/><br/> 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_spectral_ratio|H/V]] or [[Spectral_amplitudes|Spectrum]] a red dashed area will appear in the frequencies below the <math>\frac{10}{w_l}</math> frequency, as a reminder. | ||
| − | * The maximum '''upper limit''' is fixed by the [[Wikipedia:Nyquist_frequency|Nyquist frequency]], which corresponds to the half of the digitization frequency sampling. If the signal has a 100 Hz sampling frequency, the [[Wikipedia:Nyquist_frequency|Nyquist frequency]] will be 50 Hz.<br/>Above [[Wikipedia:Nyquist_frequency|Nyquist frequency]], due to the Fourier transform in itself, no data are available. So there is no need to go above the [[Wikipedia:Nyquist_frequency|Nyquist frequency]].<br/>Below [[Wikipedia:Nyquist_frequency|Nyquist frequency]], there is no lower limit to the '''upper limit''', except the '''lower limit''' frequency.<br/>In general, the '''upper limit''' is fixed in-between 10-50 Hz. | + | * The maximum '''upper limit''' is fixed by the [[Wikipedia:Nyquist_frequency|Nyquist frequency]], which corresponds to the half of the digitization frequency sampling. If the signal has a 100 Hz sampling frequency, the [[Wikipedia:Nyquist_frequency|Nyquist frequency]] will be 50 Hz.<br/>Above [[Wikipedia:Nyquist_frequency|Nyquist frequency]], due to the Fourier transform in itself, no data are available. So there is no need to go above the [[Wikipedia:Nyquist_frequency|Nyquist frequency]].<br/>Below [[Wikipedia:Nyquist_frequency|Nyquist frequency]], there is no lower limit to the '''upper limit''', except the '''lower limit''' frequency.<br/>In general, the '''upper limit''' is fixed in-between a 10-50 Hz frequency range. |
There are two options to be specified, namely Step and Number of Samples. For the Step parameter, there are two options to be selected from a drop box: Log or Linear. You might have guessed the meaning right away. When choosing Linear then the frequency axis is sampled linearly between the given limits and exactly Number of Samples will be distributed along the axis. Choosing Log accordingly samples the frequency axis logarithmically, i.e. frequency bands are close spaced at lower frequencies | There are two options to be specified, namely Step and Number of Samples. For the Step parameter, there are two options to be selected from a drop box: Log or Linear. You might have guessed the meaning right away. When choosing Linear then the frequency axis is sampled linearly between the given limits and exactly Number of Samples will be distributed along the axis. Choosing Log accordingly samples the frequency axis logarithmically, i.e. frequency bands are close spaced at lower frequencies | ||
Revision as of 10:27, 11 March 2010
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 section: where the user can fix automatic output graphics appearance parameters
- Output section section: where the user can fix where to save data
Frequency sampling section
In this section, it is possible to fix the upper and lower limits for computing.
- 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 [1], the other possibility is to define the lower frequency limit from the window length taking into account the following formula . Where is the window length and 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 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.
There are two options to be specified, namely Step and Number of Samples. For the Step parameter, there are two options to be selected from a drop box: Log or Linear. You might have guessed the meaning right away. When choosing Linear then the frequency axis is sampled linearly between the given limits and exactly Number of Samples will be distributed along the axis. Choosing Log accordingly samples the frequency axis logarithmically, i.e. frequency bands are close spaced at lower frequencies
Appearance section
automatic output graphics appearance parameters 
Output section
where to save data 
