mtmAR: Intermediate spectrum test of Thomson et al. (2001)

In astrochron: A Computational Tool for Astrochronology

Intermediate spectrum test of Thomson et al. (2001)

Description

Perform the 'intermediate spectrum test' of Thomson et al. (2001).

Paraphrased from Thomson et al. (2001): Form an intermediate spectrum by dividing MTM by AR estimate. Choose an order P for a predictor. A variety of formal methods are available in the literature, but practically, one keeps increasing P (the order) until the range of the intermediate spectrum Si(f) (equation (C4) of Thomson et al., 2001) stops decreasing rapidly as a function of P. If the intermediate spectrum is not roughly white, as judged by the minima, the value of P should be increased.

Usage

mtmAR(dat,tbw=3,ntap=NULL,order=1,method="mle",CItype=1,padfac=5,demean=T,detrend=F,
      output=1,xmin=0,xmax=Nyq,pl=1,genplot=T,verbose=T)

Arguments

dat	Stratigraphic series for analysis. First column should be location (e.g., depth), second column should be data value.
tbw	MTM time-bandwidth product.
ntap	Number of DPSS tapers to use. By default, this is set to (2*tbw)-1.
order	Order of the AR spectrum.
method	AR method ("yule-walker", "burg", "ols", "mle", "yw")
CItype	Illustrate (1) one-sided or (2) two-sided confidence intervals on plots
padfac	Pad with zeros to (padfac*npts) points, where npts is the original number of data points.
demean	Remove mean from data series? (T or F)
detrend	Remove linear trend from data series? (T or F)
output	Output (1) intermediate spectrum and confidence levels, (2) intermediate spectrum, (3) confidence levels
xmin	Smallest frequency for plotting.
xmax	Largest frequency for plotting.
pl	Plot logarithm of spectral power (1) or linear spectral power (2)?
genplot	Generate summary plots? (T or F)
verbose	Verbose output? (T or F)

Details

The power spectrum normalization approach applied here divides the Fourier coefficients by the number of points (npts) in the stratigraphic series, which is equivalent to dividing the power by (npts*npts). The (npts*npts) normalization has the convenient property whereby – for an unpadded series – the sum of the power in the positive frequencies is equivalent to half of variance; the other half of the variance is in the negative frequencies.

Note that the 'spec.mtm' function in package 'multitaper' (Rahim et al., 2014) is used for MTM spectrum estimation.

References

Rahim, K.J. and Burr W.S. and Thomson, D.J., 2014, Applications of Multitaper Spectral Analysis to Nonstationary Data. PhD thesis, Queen's University. R package version 1.0-17, https://CRAN.R-project.org/package=multitaper.

Thomson, D. J., L. J. Lanzerotti, and C. G. Maclennan, 2001, The interplanetary magnetic field: Statistical properties and discrete modes, J. Geophys.Res., 106, 15,941-15,962, doi:10.1029/2000JA000113.

See Also

eha, lowspec, mtm, mtmML96, and periodogram

Examples

# generate example series with periods of 400 ka, 100 ka, 40 ka and 20 ka
ex = cycles(freqs=c(1/400,1/100,1/40,1/20),start=1,end=1000,dt=5)

# add AR1 noise
noise = ar1(npts=200,dt=5,sd=.5)
ex[2] = ex[2] + noise[2]

# MTM spectral analysis, with conventional AR1 noise test
pl(1,title="mtmAR")
mtmAR(ex)

astrochron documentation built on Sept. 30, 2024, 9:14 a.m.