butterworth {IRISSeismic}

Apply Butterworth filter

Description

The butterworth method of Trace objects returns a new Trace where data in the @data slot have been modified by applying a Butterworth filter.

Usage

butterworth(x, n, low, high, type)

Arguments

x

a Trace object

n

filter order

low

frequency used in low- or stop/band-pass filters

high

frequency used in high or stop/band-pass filters

type

type of filter – 'low', 'high', 'pass' or 'stop'

Details

This method creates a Butterworth filter with the specified characteristics and applies it to the Trace data.

When only n and low are specified, a high pass filter is applied. When only n and high are specified, a low pass filter is applied. When n and both low and high are specified, a band pass filter is applied. To apply a band stop filter you must specify n, low, high and type='stop'

Value

A new Trace object is returned.

Author(s)

Jonathan Callahan [e-mail]

See Also

signal::butter, signal::filter

Examples

## Not run: 
# Open a connection to IRIS DMC webservices
iris <- new("IrisClient")

# Compare to the results in figure 2a of
#
# "Determination of New Zealand Ocean Bottom Seismometer Orientation
#  via Rayleigh-Wave Polarization", Stachnik et al. 
#
# http://srl.geoscienceworld.org/content/83/4/704
#
# (note: since publication, ZU.NZ19..BH1 has been renamed BH2 and ZU.NZ19..BH2 has been renamed BH1)

starttime <- as.POSIXct("2009-02-18 22:01:07",tz="GMT")
endtime <- starttime + 630
verticalLines <- starttime + seq(30,630,100)

# Get data
stZ <- getSNCL(iris,"ZU.NZ19..BHZ",starttime,endtime)
st2 <- getSNCL(iris,"ZU.NZ19..BH2",starttime,endtime)
st1 <- getSNCL(iris,"ZU.NZ19..BH1",starttime,endtime)

# Demean, Detrend, Taper
trZ <- DDT(stZ@traces[[1]],TRUE,TRUE,0.05)
tr2 <- DDT(st2@traces[[1]],TRUE,TRUE,0.05)
tr1 <- DDT(st1@traces[[1]],TRUE,TRUE,0.05)

# Bandpass filter
trZ_f <- butterworth(trZ,2,0.02,0.04,type='pass')
tr2_f <- butterworth(tr2,2,0.02,0.04,type='pass')
tr1_f <- butterworth(tr1,2,0.02,0.04,type='pass')

# 3 rows
layout(matrix(seq(3)))

# Plot
plot(trZ_f)
abline(v=verticalLines,col='gray50',lty=2)
plot(tr2_f)
abline(v=verticalLines,col='gray50',lty=2)
plot(tr1_f)
abline(v=verticalLines,col='gray50',lty=2)

# Restore default layout
layout(1)

## End(Not run)