Software:
2) Probabalistic Power Spectral
Density analysis using tools from Antelope (www.brtt.com)
dbpsdpdf is a perl
script that utilizes Antelope database functionality to compute power
spectral density estimates and then determine probability of these
spectral estimates similar to the original work by USGS (see ref). Extended reading can be found here (ref). The IRIS/DMC also makes use of this analysis - see link.
A quick link to these plots for AK network stations can be found here.
Below is a comparison between the IRIS/DMC product and the output
of dbpsdpdf for station AK_CCB for the month of 12/2011. The
daily PSD bin files were retrieved from IRIS/DMC
(http://www.iris.edu/dms/products/pdfpsd/) and plotted using the
sequence of surface commands from the included Matlab script. (A)
PSDs calculated by IRIS/DMC (B) PSDs calculated by dbwfmeas and
processed with dbpsdpdf, plotted using the same surface commands from
Matlab (C) Overlay of data from IRIS and that from dbwfmeas/dbpsdpdf.
Some further plots were made from the ensemble analysis for a month of
data. Here the IRIS/DMC figures were downloaded from the web,
rather than retrieving the raw PSD bin files. dbpsdpdf figures
were created with GMT surface routine.
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Additionally, Bob Herrman created PSD software to analyze SAC files
(http://www.eas.slu.edu/eqc/eqc_cps/SACPSD/). sacpsd computes
PSD, but does not perform the binning of PSD to determine
probability. Comparison of results from sacpsd and
dbwfmeas/dbpsdpdf is shown below for TA_121A_BHZ. A one-hour
segment during night time hours (07:00 GMT) was selected from four
different months in 2009. The comparison is shown below.
The blue line is the smoothed and resampled PSD from sacpsd, the
black line is the raw PSD as computed by dbwfmeas.
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dbpsdpdf uses dbwfmeas to calculate the PSD for a given time range. The time windowing for dbwfmeas is not straight forward or exactly the same as the IRIS/DMC product. An example dbwfmeas parameter file is below:
global_defaults &Arr{
remove_mean yes
use_det_filter yes
latency 20.0
timeout 120.0
ptype single
calib_from_calibration yes
}
measurements &Tbl{
&Arr{
type spec
channels &Tbl{
.* .*
}
rsptype A
offset 614.4
tdur 3600
twin 819.2
taper gaussian
}
}
