SeisComP3 supports string based filter definition. This section covers available filters and their parameters.
The filter definition supports building filter chains (operator >> or ->) as well as combining them with basic mathematical operators like +, -, *, /, ^ (power) and | | (absolute value).
Example:
A(1,2)>>(B(3,4)*2+C(5,6,7))>>D(8)
where A, B, C and D are different filters configured with different parameters. If a sample is filtered it passes the following stages:
s = a sample
sf = final sample
The default filter applied by scautopick is
RMHP(10)>>ITAPER(30)>>BW(4,0.7,2)>>STALTA(2,80)
It first removes the offset. Then an ITAPER of 30 seconds is applied before the data is filtered with a 4th order butterworth bandpass with corner frequencies of 0.7 Hz and 2 Hz. Finally an STA/LTA filter with a short-time time window of 2 seconds and a long-term time window of 80 seconds is applied.
Description
Calculates the average of preceding samples.
Parameters
(1) timespan in seconds
Example
AVG(20)
Calulates the average of the previous 20 seconds of data.
Description
Butterworth Bandpass filter (BW) realized as a causal recursive IIR (infinite impulse response) filter. An arbitrary bandpass filter can be created for given order and corner frequencies.
Parameters
(1) order
(2) minimum frequency
(3) maximum frequency
Example
BW(3, 0.7, 2.0)
A butterworth bandpass of 3rd order with corner frequencies of 0.7 to 2 Hz.
Description
Butterworth lowpass filter (BW_HP) realized as a causal recursive IIR (infinite impulse response) filter.
Parameters
(1) order
(2) corner frequency
Example
BW_LP(4,2)
A butterworth lowpass filter of 4th order with a corner frequencies of 2 Hz.
Description
Butterworth highpass filter (BW_HP) realized as a causal recursive IIR (infinite impulse response) filter.
Parameters
(1) order
(2) corner frequency
Example
BW_HP(4,0.7)
A butterworth highpass filter of 4th order with a corner frequencies of 0.7 Hz.
Description
Integration filter realized as a recursive IIR (infinite impulse response) integration filter. The weights are calculated according to parameter a in the following way:
a0 = (3-a)/6
a1 = 2*(3+a)/6
a2 = (3-a)/6
The integration loop calculated for each input sample s the integrated output sample s' :
v0 = s+v2;
s' = a0*v0 + a1*v1 + a2*v2;
v2 = v1
v1 = v0
Parameters
(1) coefficient a
Example
INT(0)
Integration with coefficients a0=1/2, a1=1 and a2=1/2.
Description
A one-sided cosine taper. The cosine taper is applied to a given time window in seconds.
Parameters
(1) time window in seconds
Example
ITAPER(30)
An ITAPER distorting the amplitude of the signal in the first 30 seconds by multiplying with factors between zero and one according to a half cosine function.
Description
A highpass filter realized as running mean highpass filter. For a given time window in seconds the running mean is subtracted from the single amplitude values. This is equivalent to highpass filtering the data.
Parameters
(1) time window in seconds
Example
RMHP(10)
Running mean highpass of 10 seconds that calculates the difference to the moving mean in a 10 seconds time window.
Description
A 5-second seismometer can be simulated.
Parameters
(1) Data format of the waveforms
0 displacement 1 velocity 2 acceleration
Example
SM5(1)
Simulation on velocity data.
Description
A STA/LTA filter is the ratio of a short-time average to a long-time average calculated continuously in two consecutive time windows. This method is the basis for many trigger algorithm. The short-time window is for detection of transient signal onsets whereas the long-time window provides information about the actual seismic noise at the station.
Parameters
(1) Short-time time window
(2) Long-time time window
Example
STALTA(2,60)
Computes the ratio of the average in the 2 seconds time window and the previous 60 seconds time window for moving time windows all over the trace.
Description
The simulation filter of a Wood-Anderson seismometer. The data format of the waveforms has to be given for applying the simulation filter (displacement = 0, velocity = 1, acceleration = 2), e.g. WA(1) is the simulation on velocity data.
Parameters
(1) Data format of the waveforms
0 displacement 1 velocity 2 acceleration
Example
WA(1)
Simulation on velocity data.
Description
The instrument simulation filter of a World-Wide Standard Seismograph Network (WWSSN) long-period seismometer.
Parameters
(1) Data format of the waveforms
0 displacement 1 velocity 2 acceleration
Example
WWSSN_LP(1)
Simulation on velocity data.
Description
Analog to the WWSSN_LP, the simulation filter of the short-period seismometer of the WWSSN.
Parameters
(1) Data format of the waveforms
0 displacement 1 velocity 2 acceleration
Example
WWSSN_SP(1)
Simulation on velocity data.
