Envelope of a seismic signal
The envelope method of Trace objects returns a Trace
whose data have been replaced with the envelope of the seismic signal.
envelope(x)
x |
a |
Before calculating the envelope, the seismic trace is 'cleaned up' by removing the mean, the trend and by applying a cosine taper. See DDT for more details.
The seismic envelope is defined as:
E(t) = √{T^2(t) + H^2(t)}
where T(t) is the seismic trace and H(t) is the Hilbert transform of T(t).
A Trace
whose data have been replaced with the envelope of the seismic signal.
This algorithm is adapted from code in the seewave package.
Jonathan Callahan jonathan@mazamascience.com
## Not run:
# Open a connection to IRIS DMC webservices
iris <- new("IrisClient")
starttime <- as.POSIXct("2010-02-27 06:00:00", tz="GMT")
endtime <- as.POSIXct("2010-02-27 09:00:00", tz="GMT")
# Get the waveform
st <- getDataselect(iris,"IU","ANMO","00","BHZ",starttime,endtime)
tr <- st@traces[[1]]
# Demean, detrend, cosine taper
tr <- DDT(tr)
# Create envelope version of the trace
trenv <- envelope(tr)
# Plot signal data and envelope data
plot(tr@data, type='l', col='gray80')
points(trenv@data, type='l', col='blue')
## End(Not run)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.