Difference between revisions of "Geopsy: H/V and Spectrum Toolboxes: Processing Tab"

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== Use ==
 
== Use ==
  
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This toolbox tab contains the smoothing and taper parameters for [[H/V_spectral_ratio|H/V]] or [[Spectral_amplitudes|Spectrum]] curves and the way the horizontal components are processed to compute the [[H/V_spectral_ratio|H/V]] spectral ratio, described in two sections:
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This toolbox tab contains the smoothing and taper parameters and the way the horizontal components are processed to compute the H/V spectral ratio, described in two sections:
  
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*the Parameters section (For H/V and Spectrum tools)
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*the Parameters section
  
 
*the Horizontal components section (For H/V tool only)
 
*the Horizontal components section (For H/V tool only)
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[[Image:HV_SPEC_toolb_process.png|thumb|center|300px|''Processing'' tab for smoothing parameters and horizontal components processing in H/V computing]]
 
[[Image:HV_SPEC_toolb_process.png|thumb|center|300px|''Processing'' tab for smoothing parameters and horizontal components processing in H/V computing]]
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<br style="clear: both"/>
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== Parameters section ==
 
== Parameters section ==
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=== Filter ===
 
=== Filter ===
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[[Image:HV_SPEC_toolb_process_param_taper.png|thumb|right|300px|Taper box and spin box]]When the box is checked a [[Geopsy:_Filter|filter]] is applied to each component of the entire record before selecting the stable time windows.
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[[Image:HV_SPEC_toolb_process_param_filter.png|thumb|right|300px|High-pass check-box and spin box]]When the box is checked a high-pass filter is applied along the entire record of each component before selecting the stable time windows. This procedure is used to avoid spurious frequencies due to the [[Effect of very low frequency on H/V|effect of a strong low frequency content]].
  
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Only a "High pass" filter is allowed.
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Checking this option is recommended when the signal has a strong low frequency content with respect to the frequency of interest, e.g. shallow site next to a shore line, or recording under windy condition. In such case, cutting the signal into short time windows may strongly distort the spectrum, and even using the minimum window length criteria according to the SESAME guidelines <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> (i.e. 10 times the corresponding period for the minimum frequency of interest) may not be enough to ensure a reliable H/V estimation.
  
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Sometimes, the taper size used in the pre-processing has a strong influence at low frequency. If the signal contains a strong and very low frequency component, then cutting into short time windows may strongly distort the observed spectra and H/V. Even when using the minimum window length criteria according to the SESAME guidelines <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> (i.e. 10 times the corresponding period for the minimum frequency of interest) may be not enough to ensure a reliable H/V estimation.
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This option should be used with caution. As the signal is high-pass filtered, the results below the chosen cut-off frequency could be somewhat flaky, and the cut-off frequency must be much lower than the frequency of interest.
  
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In order to avoid such “taper side effects”, signals can be high-pass filtered before computing the H/V and spectra curves.
 
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The higher value for the frequency of the high-pass filter is the minimum ‘reliable’ frequency, i.e. <math>\frac{10}{w_l}</math>, [[Effect of very low frequency on H/V]].
 
  
  
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This option should be used with caution. As the signal is high-pass filtered, the results below the chosen frequency could be somewhat flaky.
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== Horizontal components section (available only in the H/V toolbox) ==
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[[Image:HV_SPEC_toolb_process_horizontal.png|thumb|right|300px|''Horizontal components'' section for choosing how to combine the signal N-S and E-W components into a single H component)]]The H spectrum of the H/V spectral ratio is obtained by combining the N-S and E-W components of the signal.
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Three different combinations are available:
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* Squared average
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* Total horizontal energy
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* Directional energy
  
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== Horizontal components section (only available for [[H/V_spectral_ratio|HV toolbox]]) ==
 
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This section is devoted to indicate how the H/V has to be computed. There are 3 different methods that can be applied.
 
  
  
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[[Image:HV_SPEC_toolb_process_horizontal.png|thumb|right|300px|''Horizontal components'' section indicating the way H/V is processed (available for [[H/V_spectral_ratio|H/V]] computing) only]]
 
  
 
=== Squared average ===
 
=== Squared average ===
  
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The H/V is computed as followed:
 
  
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* The Fourier amplitude spectrum is computed for each window of each component (N, E and Z);
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In each window, the horizontal  spectrum is computed by a combination of the N-S and E-W components using the formula<br/><math>H(f)=\sqrt{\frac{N^2(f)+E^2(f)}{2}}</math>
  
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* The horizontal average spectrum is computed by a combination of horizontal spectra for each window, following the formula<br/><math>H(f)=\sqrt{\frac{N^2(f)+E^2(f)}{2}}</math>
 
  
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* The horizontal (averaged) and vertical spectra of each window are smoothed;
 
  
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* The horizontal to vertical ratio (H/V) is computed for each window;
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=== Total horizontal energy ===
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* The H/V is computed by averaging all H/V coming from individual windows.
 
  
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=== Total horizontal energy ===
 
  
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The H/V is computed as followed:
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In each window, the horizontal  spectrum is computed by a combination of the N-S and E-W components using the formula<br/><math>H(f)=\sqrt{N^2(f)+E^2(f)}</math>
  
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* The Fourier amplitude spectrum is computed for each window of each component (N, E and Z)
 
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* The horizontal average spectrum is computed by a combination of horizontal spectra for each window, following the formula<br/><math>H(f)=\sqrt{N^2(f)+E^2(f)}</math>
 
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* The horizontal (averaged) and vertical spectra of each window are smoothed
 
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* The horizontal to vertical ratio (H/V) is computed for each window
 
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* The H/V is computed by averaging all H/V coming from individual windows.
 
  
 
=== Directional energy ===
 
=== Directional energy ===
  
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Here, the H/V is calculated along a given direction, 0° is assumed to be the North direction and 90° the East direction. From the North-South and the East-West signals, a new (and single) signal is computed geometrically. This new signal is assumed to be the horizontal signal. The direction in which the H/V will be calculated is given in a spin box allowing changes in the direction between 0° and 180°. If the user wants to compute in a direction between 180° and 360°, due to symetry the user should take the symetrical direction: wanted direction-180°. If the user wants a 220° direction, it should be entered 40° in the spin box.
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H/V is calculated along a given direction (0° is the North direction and 90° the East direction). The N-S and E-W signals are projected onto the chosen direction.  
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<br/>H/V is computed in the direction entered in the spin box.
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* The Fourier amplitude spectrum is computed for each window of each component (recomputed horizontal and vertical)
 
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* The horizontal (recomputed) and vertical spectra of each window are smoothed
 
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* The horizontal to vertical ratio (H/V) is computed for each window
 
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* The H/V is computed by averaging all H/V coming from individual windows.
 
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== Load parameters and Start section ==
 
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The section at the bottom of the ''Time'' tab comprises two buttons.
 
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[[Image: HV_SPEC_toolb_load_start.png|thumb|left|300px|Load parameters and Start section]]
 
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<br style="clear: both"/>
 
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* The ''Load parameters'' button is used to [[Geopsy: Load Toolbox Parameters|load parameters]] from previous H/V or spectrum processing stored in a ''name.log'' file ([[Geopsy: H/V parameter file|example]]).
 
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* Press the ''Start'' button to start H/V or Spectrum processing.
 
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If no window selection has been performed, a pup-up window appears.
 
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[[Image:HV_toolbox_no_window_selected.png|thumb|left|300px|Pop-up window indicating that no window selection has been performed]]
 
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<br style="clear: both"/>
 
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Simply click on the ''Yes'' button and processing will follow its way with the current [[Geopsy: H/V and Spectrum Toolboxes| Toolbox]] parameters.
 
  
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To perform user's windowing, click on the ''No'' button.
 
  
  
 
== References ==
 
== References ==
 
<references/>
 
<references/>

Latest revision as of 13:07, 10 January 2013

Use

This toolbox tab contains the smoothing and taper parameters and the way the horizontal components are processed to compute the H/V spectral ratio, described in two sections:

  • the Parameters section
  • the Horizontal components section (For H/V tool only)


Processing tab for smoothing parameters and horizontal components processing in H/V computing



Parameters section

This section is divided in three parts:


Smoothing

Smoothing parameters

Type of smoothing applied to the windows. During the computing of H/V or Spectrum, the Fourier spectra can be smoothed (it is strongly recommended) in the goal to clarify the global aspect of the curves.

For the Spectrum computation, the Fourier spectrum from each selected time window is smoothed and then the averaged curve is computed.

For the H/V computation, the horizontal Fourier spectra (NS and EW) are first combined and then the smoothing is applied on the merged horizontal Fourier spectrum and on the vertical Fourier spectrum.


Four smoothing methods are evailable:

Smoothing option drop box
  1. Konno and Ohmachi[1] smoothing. This smoothing use a constant bandwidth in a logarithmic scale and is strongly recommended because this smoothing function preserves the different number of points at low and high frequency. This smoothing is controlled by a smoothing constant varying in-between 0 and 100. A constant of 0 gives a very strong smoothing, when a constant of 100 a very soft smoothing, more details;
  2. Constant smoothing. This smoothing function has a triangular shape centered on the current frequency and its width is equal to "Band width" given by the user. This band width varies from 0 (soft smoothing) to 100 (strong smoothing);
  3. Proportional smoothing. This smoothing function has a triangular shape and its width depends upon the current frequency. The half width is defined by percentage*frequency. The value of "percentage" cannot be greater or equal to 100% (strong smoothing).
  4. No smoothing. This can be sometime useful to have a rough idea about Fourier spectra;

The Smoothing constant spin box is used to give the smoothing constant value.

Taper

Taper box and spin box

Check the box to apply a cosine taper on both sides of the selected time windows.

A taper is used to minimize the border effects due to the extraction of a window so as to improve its properties in the frequency domain. The use of a taper is strongly recommended so as to avoid the creation of spurious frequencies.

The taper width is adjusted in the spin box.

Filter

High-pass check-box and spin box

When the box is checked a high-pass filter is applied along the entire record of each component before selecting the stable time windows. This procedure is used to avoid spurious frequencies due to the effect of a strong low frequency content.

Checking this option is recommended when the signal has a strong low frequency content with respect to the frequency of interest, e.g. shallow site next to a shore line, or recording under windy condition. In such case, cutting the signal into short time windows may strongly distort the spectrum, and even using the minimum window length criteria according to the SESAME guidelines [2] (i.e. 10 times the corresponding period for the minimum frequency of interest) may not be enough to ensure a reliable H/V estimation.

This option should be used with caution. As the signal is high-pass filtered, the results below the chosen cut-off frequency could be somewhat flaky, and the cut-off frequency must be much lower than the frequency of interest.


Horizontal components section (available only in the H/V toolbox)

Horizontal components section for choosing how to combine the signal N-S and E-W components into a single H component)

The H spectrum of the H/V spectral ratio is obtained by combining the N-S and E-W components of the signal.

Three different combinations are available:

  • Squared average
  • Total horizontal energy
  • Directional energy



Squared average

In each window, the horizontal spectrum is computed by a combination of the N-S and E-W components using the formula


Total horizontal energy

In each window, the horizontal spectrum is computed by a combination of the N-S and E-W components using the formula


Directional energy

H/V is calculated along a given direction (0° is the North direction and 90° the East direction). The N-S and E-W signals are projected onto the chosen direction.
H/V is computed in the direction entered in the spin box.


References

  1. ↑ Konno K. and T. Ohmachi, 1998. Ground motion characteristics estimated from spectral ratio between horizontal and vertical components of microtremors. Bull. seism. Soc. Am., 88-1, 228-241.
  2. ↑ Guidelines for the implementation of the H/V spectral ratio technique on ambient vibrations measurements, processing and interpretation, [1], 62 pages, April 2005
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