envelope {IRISSeismic}

Envelope of a seismic signal

Description

The envelope method of Trace objects returns a Trace whose data have been replaced with the envelope of the seismic signal.

Usage

envelope(x)

Arguments

x

a Trace object

Details

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) = \sqrt{T^2(t) + H^2(t)}

where T(t) is the seismic trace and H(t) is the Hilbert transform of T(t).

Value

A Trace whose data have been replaced with the envelope of the seismic signal.

Note

This algorithm is adapted from code in the seewave package.

Author(s)

Jonathan Callahan [e-mail]

Examples

## 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)