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##
## Metric to calculate STA/LTA metric for a Stream of seismic data
##
## 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
################################################################################
# This metric returns the maximum value of the STA/LTA algorithm applied to this
# stream's data with the following parameters passed to the STALTA method:
#
# staSecs = 3
# ltaSecs = 30
# algorithm = "classic_RR" | "classic_LR" (default) | "classic_LR2" | "EarleAndShearer_envelope | Wong_MER"
STALTAMetric <- function(st, staSecs=3, ltaSecs=30, increment=1, algorithm="classic_LR") {
starttime <- st@requestedStarttime
endtime <- st@requestedEndtime
# Make sure we're working with a single snclq
unique_ids <- uniqueIds(st)
if (length(unique_ids) > 1) {
stop(paste("STALTAMetric: Stream has",unique_ids,"unique identifiers"))
}
snclq <- unique_ids[1]
# Preprocessing parameters passed to STALTA
demean <- TRUE
detrend <- TRUE
taper <- 0.0
maxSTALTA <- 0.0
eventTime <- starttime
# Loop through all traces
for (trace in st@traces) {
# Make sure trace has enough data
nlta <- ltaSecs * trace@stats@sampling_rate
nsta <- staSecs * trace@stats@sampling_rate
if (length(trace) <= (nlta+nsta)) {
next
}
# Get a vector of STALTA values
if (algorithm == "classic_LR") { # attempt to reduce memory usage
n_sta <- staSecs * trace@stats@sampling_rate
n_lta <- ltaSecs * trace@stats@sampling_rate
stalta <- seismicRoll::roll_stalta((as.numeric(pracma::detrend(trace@data, tt='linear')))^2, n_sta, n_lta, increment)
} else {
stalta <- STALTA(trace, staSecs, ltaSecs, algorithm, demean, detrend, taper, increment)
}
stalta[is.infinite(stalta)] <- NA # when result blows up to infinity, replace with NA
if(all(is.na(stalta))) {
stop("STALTAMetric: stalta returns a vector with all NA or NaN")
}
traceMaxSTALTA <- max(stalta, na.rm=TRUE)
# Calculate the time at which this STALTA maximum occurred
eventIndex <- which(stalta == traceMaxSTALTA)[1]
traceEventTime <- trace@stats@starttime + eventIndex / trace@stats@sampling_rate
if (traceMaxSTALTA > maxSTALTA) {
maxSTALTA <- traceMaxSTALTA
eventTime <- traceEventTime
}
}
# Create and return a list of Metric objects
m1 <- new("GeneralValueMetric", snclq=snclq, starttime=starttime, endtime=endtime, metricName="max_stalta",
elementNames=c("value","time"), elementValues=c(maxSTALTA, eventTime),
valueStrings=c(format(maxSTALTA), format(eventTime,format="%Y-%m-%dT%H:%M:%S")))
return(c(m1))
}
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