Geopsy: H/V and Spectrum Toolboxes: Processing Tab - Revision history

Gaillot at 13:07, 10 January 2013

2013-01-10T13:07:56Z

Gaillot: /* Use */

2013-01-10T13:06:41Z

Use

Gaillot at 13:03, 10 January 2013

2013-01-10T13:03:59Z

Gaillot at 12:22, 10 January 2013

2013-01-10T12:22:17Z

Gaillot: /* Horizontal components section (only available for HV toolbox) */

2013-01-10T12:19:24Z

Horizontal components section (only available for HV toolbox)

Gaillot: /* Filter */

2013-01-10T11:47:30Z

Filter

Gaillot at 10:44, 10 January 2013

2013-01-10T10:44:43Z

Gaillot: /* Taper */

2013-01-10T10:34:25Z

Taper

Gaillot: /* Smoothing */

2013-01-10T10:28:02Z

Smoothing

Gaillot: /* Parameters section */

2013-01-09T17:21:04Z

Parameters section

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 == Use ==
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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]]
 == Parameters section ==

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 == Use ==
-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:
+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
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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]]
 == Parameters section ==

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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:
-*the Parameters section (For H/V and Spectrum tools)
+*the Parameters section
 *the Horizontal components section (For H/V tool only)

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 == Use ==
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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]]
 == Parameters section ==
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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.
 == Horizontal components section (available only in the H/V toolbox) ==
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 <br/>H/V is computed in the direction entered in the spin box.
 == References ==
 <references/>

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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.
-== Horizontal components section (only available for [[H/V_spectral_ratio|HV toolbox]]) ==
+== Horizontal components section (available only in the H/V toolbox) ==
-This section is devoted to indicate how the H/V has to be computed. There are 3 different methods that can be applied.
+[[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.
 === Squared average ===
-* The Fourier amplitude spectrum is computed for each window of each component (N, E and Z);
+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>
-* The horizontal to vertical ratio (H/V) is computed for each window;
+=== Total horizontal energy ===
-The H/V is computed as followed:
+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>
 === Directional energy ===
-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.
+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.
+<br/>H/V is computed in the direction entered in the spin box.
 == Load parameters and Start section ==

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 === Filter ===
-[[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.
+[[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]].
-Only a "High pass" filter is allowed.
+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.
-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.
+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 (only available for [[H/V_spectral_ratio|HV toolbox]]) ==

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 === Taper ===
-Use or not of a [[Geopsy:_Taper|cosine taper]] on each of the selected time windows.
+[[Image:HV_SPEC_toolb_process_param_taper.png|thumb|right|300px|Taper box and spin box]]Check the box to apply a [[Geopsy:_Taper|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 [[Geopsy:_Taper|taper]] is strongly recommended so as to avoid the creation of weird frequencies.
+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 [[Geopsy:_Taper|taper]] is strongly recommended so as to avoid the creation of spurious frequencies.
 The taper width is adjusted in the spin box.
 === Filter ===
-Fixing the use or not of a [[Geopsy:_Filter|filter]] on the whole signal.
+[[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.
-This option allows to filter the signal before the extraction of the time windows.
+Only a "High pass" filter is allowed.
-To the contrary of the [[Geopsy: Waveform Menu|Waveform menu filter]] there is only a "High pass" filter allowed, rejecting frequencies below a given value
+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.
-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 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.
+In order to avoid such “taper side effects”, signals can be high-pass filtered before computing the H/V and spectra curves.
 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]].
- This option should be used with caution. As the signal is high-pass filtered, the results below the chosen frequency could be somewhat flaky.
+This option should be used with caution. As the signal is high-pass filtered, the results below the chosen frequency could be somewhat flaky.
 == Horizontal components section (only available for [[H/V_spectral_ratio|HV toolbox]]) ==

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 <br style="clear: both"/>
-Four smoothing method are evailable:
+Four smoothing methods are evailable:
 [[Image:Process_param_smoothingtypes.png|thumb|right|300px|Smoothing option drop box]]
 #''Konno and Ohmachi''<ref>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.</ref> 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, [[Smoothing_details|more details]];
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 The ''Smoothing constant'' spin box is used to give the smoothing constant value.
 === Taper ===

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 == Parameters section ==
-[[Image:HV_SPEC_toolb_process_param.png|thumb|right|300px|''Processing'' tab giving access to smoothing, parameters (for windows) and how is processed the H/V (available only for [[H/V_spectral_ratio|H/V]] computing)]]
+This section is divided in three parts:
 === Smoothing ===
-Type of smoothing applied to the windows (2 first lines).
+[[Image:HV_SPEC_toolb_process_param.png|thumb|right|300px|Smoothing parameters]]
-During the computing of [[H/V_spectral_ratio|H/V]] or [[Spectral_amplitudes|Spectrum]], the Fourier spectra can be smoothed (it is strongly recommanded) in the goal to clarify the global aspect of the curves.
+Type of smoothing applied to the windows.
-For [[Spectral_amplitudes|Spectrum]], each Fourier spectrum (coming from a window) is smoothed and then the averaged curve is computed.
+For the Spectrum computation, the Fourier spectrum from each selected time window is smoothed and then the averaged curve is computed.
-For [[H/V_spectral_ratio|H/V]], the horizontal Fourier spectra (NS and EW, coming from a synchronous window) are first added and then the smoothing is applied on the merged horizontal Fourier spectrum and on the vertical Fourier spectrum.
+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.
 <br style="clear: both"/>
-Four possibilities are displayed:
+Four smoothing method are evailable:
 [[Image:Process_param_smoothingtypes.png|thumb|right|300px|Smoothing option drop box]]
-#''No smoothing''. This can be sometime usefull to have a rough idea about Fourier spectra;
+#''Konno and Ohmachi''<ref>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.</ref> 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, [[Smoothing_details|more details]];
 #''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);
 #''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).
-Except for ''No smoothing'', the constants linked to the other smoothing methods can be fixed using a spin box.
+The ''Smoothing constant'' spin box is used to give the smoothing constant value.
 === Taper ===