Data Services Products: Noise Toolkit ME Noise Toolkit Microseism Energy (ME) bundle

Bundle Content

The Noise Toolkit ME bundle is a collection of 3 Python scripts that are configurable and allow users to conveniently calculate and plot ME temporal variations in period bands of interest. By default, the bundle is configured to calculate ME over period band of 1-5 s for small local storms recorded by coastal stations, 5-10 s for the SMs, 11-30 s for the primary microseisms and 50-200 s for the Earth hum using PSDs of three-component broadband seismic data (BH channels). The stored ME values could be smoothed using a median sliding time window (e.g. 6 hours, 12 hours, 1 day, 4 days, and 16 days). The included scripts are:

1. ntk_computePower.py – a Python script to calculate power of each PSD window (by default 1 hour) over selected bins (period bands)
2. ntk_medianPower.py – a Python script to calculate median power from the PSD powers (by default hourly PSD power) using a sliding window of a given length (e.g., 12 hours)
3. ntk_plotPower.py – a Python script to plot median powers computed from a series of PSD powers

Power Computation

PSDs are converted to power by running the ntk_computePower.py script. The script reads its run-time parameters from a file provided by user in addition to its command line arguments. A typical command for running this script is as follows:

python bin/ntk_computePower.py param=computePower net=IU sta=GUMO loc=00 chan=BHZ type=period mode=0  
file=IU.GUMO.00.BHZ.2014-10-01T00:00:00.2014-10-20T00:00:00.period.txt

where:

• param=computePower specifies name of a Python (.py) file under the param directory that contains the run-time parameters
• type=period specifies domain of the PSDs
• mode=0 instructs the script NOT to display additional information during its run
  
• file=IU.GUMO.00.BHZ.2014-10-01T00:00:00.2014-10-20T00:00:00.period.txt specifies the combined PSD file that contains the PSDs for the interval of interest.

NOTE: For an efficient PSD extraction and power computation, the PSD file should have the same format as the output of the ntk_extractPsdHour.py script of the Noise Toolkit PDF-PSD bundle or PQLX’s exPSDhour script

Power is computed from PSDs using a simple integration technique (see figure to the right). Each PSD is converted to power by first breaking it into bins that represent period bands of interest. Then, power for each bin is obtained by converting each PSD value from dB to power and then multiplying by the offset distance (in Hz) to the next sample. Power for the entire bin is obtained by adding powers of all contributing PSD samples. This results in one power sample per PSD curve for each bin. Below is a sample output file from the above command for PSDs that are computed using 1 hour windows with 50% overlap (one power sample every 30 minutes):

Periods
                Date                 Time         local (1-5)           SM (5-10)          PM (11-30)        HUM (50-200)
          2014-10-01             00:00:00         1.18890e-11         5.03817e-13         1.49771e-17         3.20741e-20
          2014-10-01             00:30:00         1.22370e-11         6.31169e-13         1.33142e-17         3.63793e-20
          2014-10-01             01:00:00         1.27324e-11         7.85485e-13         4.74540e-17         8.48310e-20
          2014-10-01             01:30:00         1.37405e-11         7.80567e-13         9.15223e-17         9.58233e-20
          2014-10-01             02:00:00         1.38827e-11         7.22432e-13         2.41254e-17         2.37568e-20
          2014-10-01             02:30:00         1.25710e-11         7.94107e-13         3.18788e-17         3.25338e-20
          2014-10-01             03:00:00         1.52942e-11         1.24658e-12         7.14022e-14         3.16893e-17
          2014-10-01             03:30:00         1.57826e-11         1.12342e-12         7.49102e-14         3.28168e-17

Median ME

Once PSDs are converted to power, user can run a series of sliding windows of fixed width (e.g. 6 hours, 12 hours, 1 day, 4 days, and 16 days) over the computed power values to obtain short-term to long-term ME variation patterns for the station.

Median powers are computed using the ntk_medianPower.py script. The script reads its run-time parameters from a file provided by user in addition to its command line arguments. A typical command for running this script is as follows:

python bin/ntk_medianPower.py param=medianPower  net=IU sta=GUMO loc=00 chan=BHZ start=2014-10-01T00:00:00 end=2014-10-20T00:00:00  win=12 mode=0 
file=IU.GUMO.00.BHZ.2014-10-01T00:00:00.2014-10-20T00:00:00.txt

where:

• param=computePower specifies name of a Python (.py) file under the param directory that contains the run-time parameters
• win=12 specifies that computation should be done by calculating median of power over a 12 hour sliding window.
• file=IU.GUMO.00.BHZ.2014-10-01T00:00:00.2014-10-20T00:00:00.txt specifies the file produced by running the ntk_computePower.py script (the file name is printed at the end of the ntk_computePower.py execution).

Below is a sample output file from the above command:

Period
           Date-Time         local (1-5)           SM (5-10)          PM (11-30)        HUM (50-200)
2014-10-01T00:00:00.0         1.38611e-11         7.94107e-13         4.74540e-17         9.88739e-20
2014-10-01T00:10:00.0         1.38611e-11         7.94107e-13         4.74540e-17         9.88739e-20
2014-10-01T00:20:00.0         1.38611e-11         7.94107e-13         4.74540e-17         9.88739e-20
2014-10-01T00:30:00.0         1.38008e-11         7.89796e-13         3.97011e-17         9.73486e-20
2014-10-01T00:40:00.0         1.38008e-11         7.89796e-13         3.97011e-17         9.73486e-20
2014-10-01T00:50:00.0         1.38008e-11         7.89796e-13         3.97011e-17         9.73486e-20
2014-10-01T01:00:00.0         1.37405e-11         7.85485e-13         3.19483e-17         9.58233e-20
2014-10-01T01:10:00.0         1.37405e-11         7.85485e-13         3.19483e-17         9.58233e-20

Plotting Median ME

Plot of the median ME values, like the above images, are obtained by running the ntk_plotPower.py script. A typical command for running this script is as follows:

python bin/ntk_plotPower.py param=plotPower net=IU sta=GUMO loc=00 chan=BHZ start=2014-10-01T00:00:00 end=2014-10-20T00:00:00 win=12 
file=IU.GUMO.00.BHZ.2014-10-01T00:00:00.2014-10-20T00:00:00.12h.txt bin=SM mode=0 ymax=20

where:

• param=plotPower specifies name of a Python (.py) file under the param directory that contains the run-time parameters and
• mode=0 instructs the script NOT to display additional information during its run
• file=IU.GUMO.00.BHZ.2014-10-01T00:00:00.2014-10-20T00:00:00.12h.txt specifies the file that contains the median power for the interval of interest
• bin=SM indicates that SM bin values should be plotted (SM band is defined in the parameter file)
• ymax=7 sets the maximum for the y-axis.