Geopsy: STA/LTA - Revision history

Clotaire Michel: /* Use */

2010-03-12T13:47:03Z

Use

Pierre-Yves Bard: /* Parameters in Geopsy */

2010-03-12T09:40:20Z

Parameters in Geopsy

Pierre-Yves Bard: /* Anti-triggering algorithm */

2010-03-12T09:28:40Z

Anti-triggering algorithm

Pierre-Yves Bard: /* Anti-triggering algorithm */

2010-03-12T09:24:27Z

Anti-triggering algorithm

Pierre-Yves Bard at 09:20, 12 March 2010

2010-03-12T09:20:16Z

Pierre-Yves Bard at 09:14, 12 March 2010

2010-03-12T09:14:58Z

Pierre-Yves Bard at 09:12, 12 March 2010

2010-03-12T09:12:49Z

Clotaire Michel at 09:55, 11 March 2010

2010-03-11T09:55:40Z

Clotaire Michel: New page: The '''Anti-triggering algorithm STA/LTA''' (Short Time Average on Long Time Average) is a algorithm based on average amplitudes to reject energy burst in signal time histories. '''STA/LTA...

2010-03-11T09:05:21Z

New page: The '''Anti-triggering algorithm STA/LTA''' (Short Time Average on Long Time Average) is a algorithm based on average amplitudes to reject energy burst in signal time histories. '''STA/LTA...

New page

The '''Anti-triggering algorithm STA/LTA''' (Short Time Average on Long Time Average) is a algorithm based on average amplitudes to reject energy burst in signal time histories. '''STA/LTA''' is a tool reached from the [[Geopsy: Waveform Menu|Waveform menu]], that computes the ratio STA over LTA of the signals in the active [[Geopsy: Signal Viewer|signal viewer]]. The anti-triggering algorithm STA/LTA can be used in most of [[Geopsy: Tools|advanced signal processing tools]] to process only on stationary signal time windows.

==Use==
''STA/LTA'' in the [[Geopsy: Waveform Menu|Waveform menu]] is a tool designed to show the typical values of ''STA/LTA'' to decide for appropriate limits in the anti-triggering algorithm. ''STA/LTA'' modifies the [[Geopsy: Temporary Signal|temporary signals]] in the active viewer.
In the advanced signal processing tools, the parameters for the ''STA/LTA anti-triggering algorithm'' can be set in the ''Raw signal'' sub-tab of the ''Time tab''.

==STA/LTA computation==
[[Image:STALTA.png|thumb|right|250px|STA/LTA pop-up window.]]
''STA/LTA'' is the ratio between the amplitude, here computed as the L1 norm (average of the absolute values), of the signal on a short time window of length ''STA'' and on a long time window of length ''LTA''. At a given point ''STA/LTA'' is computed for the time windows preceding the point. For the first signal points, where there are not enough preceding data points to compute the whole LTA and/or STA, the average of the whole signal is used for the missing points.
[[Image:STALTAEx.png|thumb|center|300px|STA/LTA ratio for an example signal.]]

==Anti-triggering algorithm==
[[Image:STALTAAlgo.png|thumb|right|250px|Anti-triggering algorithm parameters.]]
The anti-triggering algorithm aims at selecting only the signal parts for which the signal is stationary, i.e. ''STA/LTA'' stays in a given range of values. The upper bound of STA/LTA aims at avoiding energy bursts, produced for example by pedestrians walking next to a sensor.

This implementation differs from the original implementation that uses the L2 norm instead of L1 norm, that is more appropriate in a theoretical point of view because it represents the energy of the signal and allows a statistical hypothesis test on the stationarity of the signal. However, this implementation, that does not change much the results, benefits from the experience of the community concerning the threshold values that should be used.
[[Image:STALTAEx.png|thumb|center|300px|Anti-triggering algorithm used to select stationary time windows.]]

==Parameters in Geopsy==
By clicking on ''STA/LTA'' in the [[Geopsy: Waveform Menu|Waveform menu]], a pop-up window appears with the following parameters:
*STA is the Short Time window length in seconds. The default value is 1 s.
*LTA is the Long Time window length in seconds. The default value is 30 s.
These parameters are enough to compute STA/LTA for each data point. These values are related to the time recurrence and length of the undesired signals that should be removed.
In the [[Geopsy: Tools|advanced signal processing tools]], additional parameters are needed to use the anti-triggering algorithm:
*Min STA/LTA is the lower limit for the STA/LTA ratio. The default value is 0.2.
*Max STA/LTA is the upper limit for the STA/LTA ratio. The default value is 2.5.
In ambient vibration applications, the upper limit is the most important and should be trade-off between stationarity and usable signal length. These values can be adapted to each dataset using the '''STA/LTA''' tool in the [[Geopsy: Waveform Menu|Waveform menu]]. However, it is advised not to loose too much time trying to fix these values.

@@ Line 14: / Line 14: @@
 The anti-triggering algorithm aims at selecting only the signal parts for which the signal amplitude is quasi-stationary, i.e. for which the ''STA/LTA'' ratio stays within a limited range of values around 1. The upper bound of STA/LTA aims at avoiding energy bursts, produced for example by pedestrians walking next to a sensor.
-This implementation differs from the original implementation that uses the L2 norm instead of L1 norm, that is more appropriate in a theoretical point of view because it represents the energy of the signal and allows a statistical hypothesis test on the stationarity of the signal. This implementation was practically used in seismology to decrease the computation time. It does not change much the results and benefits from the experience of the community concerning the threshold values that should be used.
+This implementation differs from the original implementation that uses the L2 norm instead of L1 norm, that is more appropriate in a theoretical point of view because it represents the energy of the signal and allows a statistical hypothesis test on the stationarity of the signal. This L1 implementation was used in early seismological applications to decrease the computation time. It does not change much the results and benefits from the experience of the community concerning the threshold values that should be used.
 [[Image:STALTAWin.png|thumb|center|400px|Anti-triggering algorithm used to select stationary time windows.]]

@@ Line 12: / Line 12: @@
 ==Anti-triggering algorithm==
 [[Image:STALTAAlgo.png|thumb|right|200px|Anti-triggering algorithm parameters.]]
-The anti-triggering algorithm aims at selecting only the signal parts for which the signal is stationary, i.e. ''STA/LTA'' stays in a given range of values. The upper bound of STA/LTA aims at avoiding energy bursts, produced for example by pedestrians walking next to a sensor.
+The anti-triggering algorithm aims at selecting only the signal parts for which the signal amplitude is quasi-stationary, i.e. for which the ''STA/LTA'' ratio stays within a limited range of values around 1. The upper bound of STA/LTA aims at avoiding energy bursts, produced for example by pedestrians walking next to a sensor.
 This implementation differs from the original implementation that uses the L2 norm instead of L1 norm, that is more appropriate in a theoretical point of view because it represents the energy of the signal and allows a statistical hypothesis test on the stationarity of the signal. This implementation was practically used in seismology to decrease the computation time. It does not change much the results and benefits from the experience of the community concerning the threshold values that should be used.

← Older revision		Revision as of 09:20, 12 March 2010
Line 1:		Line 1:
−	The '''Anti-triggering algorithm STA/LTA''' (Short Time Average over Long Time Average) ~~is an algorithm based on average amplitudes~~ to reject energetic transients from ambient vibration recordings. '''STA/LTA''' ~~is a~~ tool reached from the [[Geopsy: Waveform Menu\|Waveform menu]], ~~that computes~~ the ~~ratio~~ STA ~~over~~ LTA of the signals in the active [[Geopsy: Signal Viewer\|signal viewer]]. The anti-triggering algorithm STA/LTA can be used in most of [[Geopsy: Tools\|advanced signal processing tools]] to process the signals only on stationary time windows.	+	The '''Anti-triggering algorithm STA/LTA''' (Short Time Average over Long Time Average) has been designed to reject energetic transients from ambient vibration recordings, in view of keeping only (quasi-)stationary windows . The '''STA/LTA''' tool, reached from the [[Geopsy: Waveform Menu\|Waveform menu]], is based on the comparison of short term average amplitude ('''''STA''''') and long term average ('''''LTA''''') of the signals in the active [[Geopsy: Signal Viewer\|signal viewer]]. The anti-triggering algorithm STA/LTA can be used in most of [[Geopsy: Tools\|advanced signal processing tools]] to process the signals only on stationary time windows.

	==Use==		==Use==

← Older revision		Revision as of 09:14, 12 March 2010
Line 1:		Line 1:
−	The '''Anti-triggering algorithm STA/LTA''' (Short Time Average over Long Time Average) is a algorithm based on average amplitudes to reject ~~energy bursts in signal time histories~~. '''STA/LTA''' is a tool reached from the [[Geopsy: Waveform Menu\|Waveform menu]], that computes the ratio STA over LTA of the signals in the active [[Geopsy: Signal Viewer\|signal viewer]]. The anti-triggering algorithm STA/LTA can be used in most of [[Geopsy: Tools\|advanced signal processing tools]] to process the signals only on stationary time windows.	+	The '''Anti-triggering algorithm STA/LTA''' (Short Time Average over Long Time Average) is an algorithm based on average amplitudes to reject energetic transients from ambient vibration recordings. '''STA/LTA''' is a tool reached from the [[Geopsy: Waveform Menu\|Waveform menu]], that computes the ratio STA over LTA of the signals in the active [[Geopsy: Signal Viewer\|signal viewer]]. The anti-triggering algorithm STA/LTA can be used in most of [[Geopsy: Tools\|advanced signal processing tools]] to process the signals only on stationary time windows.

	==Use==		==Use==

← Older revision		Revision as of 09:12, 12 March 2010
Line 1:		Line 1:
−	The '''Anti-triggering algorithm STA/LTA''' (Short Time Average on Long Time Average) is a algorithm based on average amplitudes to reject energy bursts in signal time histories. '''STA/LTA''' is a tool reached from the [[Geopsy: Waveform Menu\|Waveform menu]], that computes the ratio STA over LTA of the signals in the active [[Geopsy: Signal Viewer\|signal viewer]]. The anti-triggering algorithm STA/LTA can be used in most of [[Geopsy: Tools\|advanced signal processing tools]] to process the signals only on stationary time windows.	+	The '''Anti-triggering algorithm STA/LTA''' (Short Time Average over Long Time Average) is a algorithm based on average amplitudes to reject energy bursts in signal time histories. '''STA/LTA''' is a tool reached from the [[Geopsy: Waveform Menu\|Waveform menu]], that computes the ratio STA over LTA of the signals in the active [[Geopsy: Signal Viewer\|signal viewer]]. The anti-triggering algorithm STA/LTA can be used in most of [[Geopsy: Tools\|advanced signal processing tools]] to process the signals only on stationary time windows.

	==Use==		==Use==

@@ Line 2: / Line 2: @@
 ==Use==
-''STA/LTA'' in the [[Geopsy: Waveform Menu|Waveform menu]] is a tool designed to show the typical values of ''STA/LTA'' to decide for appropriate limits in the anti-triggering algorithm. ''STA/LTA'' modifies the [[Geopsy: Temporary Signal|temporary signals]] in the active viewer.
+''STA/LTA'' in the [[Geopsy: Waveform Menu|Waveform menu]] is a tool designed to show the typical values of ''STA/LTA'' to decide for appropriate limits in the anti-triggering algorithm. ''STA/LTA'' creates new [[Geopsy: Temporary Signal|temporary signals]] in the active viewer.
 In the advanced signal processing tools, the parameters for the ''STA/LTA anti-triggering algorithm'' can be set in the ''Raw signal'' sub-tab of the ''Time tab''.

@@ Line 22: / Line 22: @@
 *STA is the Short Time window length in seconds. The default value is 1 s.
 *LTA is the Long Time window length in seconds. The default value is 30 s.
-These parameters are enough to compute STA/LTA for each data point. These values are related to the time recurrence and length of the undesired signals that should be removed.
+These parameters are enough to compute STA/LTA for each data point and allow to identify the time occurrence and duration of the energetic transients.
-In the [[Geopsy: Tools|advanced signal processing tools]], additional parameters are needed to use the anti-triggering algorithm:
 *Min STA/LTA is the lower limit for the STA/LTA ratio. The default value is 0.2.
 *Max STA/LTA is the upper limit for the STA/LTA ratio. The default value is 2.5.
-In ambient vibration applications, the upper limit is the most important and should be trade-off between stationarity and usable signal length. These values can be adapted to each dataset using the '''STA/LTA''' tool in the [[Geopsy: Waveform Menu|Waveform menu]]. However, it is advised not to loose too much time trying to fix these values.
+In ambient vibration applications, the upper limit is the most important : its value controls the trade-off between stationarity and usable signal length. These values can be adapted to each dataset using the '''STA/LTA''' tool in the [[Geopsy: Waveform Menu|Waveform menu]]. However, it is advised not to loose too much time trying to fix these values.
 ==References==
 * For a review: Withers M., Aster R., Young C., Beiriger J., Harris M., Moore S. and Trujillo, J.. A Comparison of Select Trigger Algorithms for Automated Global Seismic Phase and Event Detection. Bulletin of the Seismological Society of America, Vol. 88, No. 1, pp. 95-106, February 1998.

@@ Line 1: / Line 1: @@
-The '''Anti-triggering algorithm STA/LTA''' (Short Time Average on Long Time Average) is a algorithm based on average amplitudes to reject energy burst in signal time histories. '''STA/LTA''' is a tool reached from the [[Geopsy: Waveform Menu|Waveform menu]], that computes the ratio STA over LTA of the signals in the active [[Geopsy: Signal Viewer|signal viewer]]. The anti-triggering algorithm STA/LTA can be used in most of [[Geopsy: Tools|advanced signal processing tools]] to process only on stationary signal time windows.
+The '''Anti-triggering algorithm STA/LTA''' (Short Time Average on Long Time Average) is a algorithm based on average amplitudes to reject energy bursts in signal time histories. '''STA/LTA''' is a tool reached from the [[Geopsy: Waveform Menu|Waveform menu]], that computes the ratio STA over LTA of the signals in the active [[Geopsy: Signal Viewer|signal viewer]]. The anti-triggering algorithm STA/LTA can be used in most of [[Geopsy: Tools|advanced signal processing tools]] to process the signals only on stationary time windows.
 ==Use==
@@ Line 6: / Line 6: @@
 ==STA/LTA computation==
-[[Image:STALTA.png|thumb|right|250px|STA/LTA pop-up window.]]
+[[Image:STALTA.png|thumb|right|200px|STA/LTA pop-up window.]]
 ''STA/LTA'' is the ratio between the amplitude, here computed as the L1 norm (average of the absolute values), of the signal on a short time window of length ''STA'' and on a long time window of length ''LTA''. At a given point ''STA/LTA'' is computed for the time windows preceding the point. For the first signal points, where there are not enough preceding data points to compute the whole LTA and/or STA, the average of the whole signal is used for the missing points.
-[[Image:STALTAEx.png|thumb|center|300px|STA/LTA ratio for an example signal.]]
+[[Image:STALTAEx.png|thumb|center|400px|STA/LTA ratio for an example signal.]]
 ==Anti-triggering algorithm==
-[[Image:STALTAAlgo.png|thumb|right|250px|Anti-triggering algorithm parameters.]]
+[[Image:STALTAAlgo.png|thumb|right|200px|Anti-triggering algorithm parameters.]]
 The anti-triggering algorithm aims at selecting only the signal parts for which the signal is stationary, i.e. ''STA/LTA'' stays in a given range of values. The upper bound of STA/LTA aims at avoiding energy bursts, produced for example by pedestrians walking next to a sensor.
-This implementation differs from the original implementation that uses the L2 norm instead of L1 norm, that is more appropriate in a theoretical point of view because it represents the energy of the signal and allows a statistical hypothesis test on the stationarity of the signal. However, this implementation, that does not change much the results, benefits from the experience of the community concerning the threshold values that should be used.
+This implementation differs from the original implementation that uses the L2 norm instead of L1 norm, that is more appropriate in a theoretical point of view because it represents the energy of the signal and allows a statistical hypothesis test on the stationarity of the signal. This implementation was practically used in seismology to decrease the computation time. It does not change much the results and benefits from the experience of the community concerning the threshold values that should be used.
-[[Image:STALTAEx.png|thumb|center|300px|Anti-triggering algorithm used to select stationary time windows.]]
+[[Image:STALTAWin.png|thumb|center|400px|Anti-triggering algorithm used to select stationary time windows.]]
 ==Parameters in Geopsy==
 By clicking on ''STA/LTA'' in the [[Geopsy: Waveform Menu|Waveform menu]], a pop-up window appears with the following parameters:
 *STA is the Short Time window length in seconds. The default value is 1 s.
@@ Line 26: / Line 27: @@
 *Max STA/LTA is the upper limit for the STA/LTA ratio. The default value is 2.5.
 In ambient vibration applications, the upper limit is the most important and should be trade-off between stationarity and usable signal length. These values can be adapted to each dataset using the '''STA/LTA''' tool in the [[Geopsy: Waveform Menu|Waveform menu]]. However, it is advised not to loose too much time trying to fix these values.