Nothing

```
##
## Metric to calculate a signal/noise ratio comparing the rmsVariance (power)
## by dividing the incoming stream into two equal parts. It is assumed that
## the stream starttime and endtime are equally spaced about the onset of
## of a seismic event.
##
## Copyright (C) 2012 Mazama Science, Inc.
## by Jonathan Callahan, jonathan@mazamascience.com
##
## This program is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2 of the License, or
## (at your option) any later version.
##
## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with this program; if not, write to the Free Software
## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
################################################################################
#
SNRMetric <- function(st, algorithm="splitWindow", windowSecs=60) {
# Extract the trace and associated information
tr <- st@traces[[1]]
snclq <- tr@id
starttime <- tr@stats@starttime
endtime <- tr@stats@endtime
# Check for gaps
if (length(st@traces) > 1) {
stop(paste("SNRMetric: skipping", snclq, "because it has gaps"))
}
# Bail out if we have don't have enough data
if (as.numeric(difftime(endtime, starttime, units="sec")) < windowSecs) {
stop(paste("SNRMetric: Data do not fill the window."))
}
# Bail out if we have a DC signal
if (isDC(tr)) {
stop(paste("SNRMetric: Trace data is a DC signal."))
}
if (algorithm == "splitWindow") {
# NOTE: In this case, the window is assumed to be centered about
# NOTE: an event, perhaps determined withthe IRIS DMC "event" webservice
# NOTE: The triggerOnset is just the midpoint of the trace.
to <- starttime + as.numeric(difftime(endtime, starttime, units="sec")) / 2
trN <- IRISSeismic::slice(tr, to-windowSecs/2, to)
trS <- IRISSeismic::slice(tr, to, to+windowSecs/2)
snr <- rmsVariance(trS) / rmsVariance(trN)
} else if (algorithm == "staltaTrigger") {
# Demean and detrend the data first
tr <- DDT(tr, TRUE, TRUE, 0)
# Find the P-wave onset with "classic_LR"
staSecs <- 3
ltaSecs <- 30
# Make sure that there are at least two points in the STA window
if (staSecs * tr@stats@sampling_rate < 1) {
staSecs <- 2 / tr@stats@sampling_rate
ltaSecs <- staSecs * 5
}
picker <- STALTA(tr,staSecs,ltaSecs,"classic_LR")
to <- triggerOnset(tr,picker)
trN <- IRISSeismic::slice(tr, to-windowSecs/2, to)
trS <- IRISSeismic::slice(tr, to, to+windowSecs/2)
snr <- rmsVariance(trS) / rmsVariance(trN)
}
# Create and return a list of Metric objects
#m1 <- new("SingleValueMetric", snclq=snclq, starttime=starttime, endtime=endtime, metricName="sample_snr", value=snr)
m1 <- new("GeneralValueMetric", snclq=snclq, starttime=starttime, endtime=endtime, metricName="sample_snr",
elementNames=c("value"), elementValues=snr)
return(c(m1))
}
```

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