DiffusionTF: Diffusion transfer function

In EarthSystemDiagnostics/proxysnr: Separate Signal and Noise in Climate Proxy Records

Description

This function implements an empirical Monte Carlo approach to estimate the spectral transfer function for the effect of firn diffusion on the spatial average of firn/ice-core stable isotope records.

Usage

DiffusionTF(nt, nc, ns, sigma, res = 1, coherent = FALSE, ...)

Arguments

nt	the length of the modelled isotope records (i.e. the number of data points in each record)
nc	the number of cores in the modelled core array
ns	the number of Monte Carlo simulations for estimating the transfer function
sigma	numeric vector of length nt or numeric array of dimension nt * nc providing diffusion length values. The nt diffusion length values are assumed to correspond to the respective nt isotope values. If only a numeric vector is provided, it is assumed that these diffusion lengths are valid for all nc cores. If an array is provided, each column provides the diffusion lengths for the respective core. Note that the units of the diffusion length must match the units of res.
res	the sampling (e.g., temporal) resolution of the isotope data; determines the frequency axis of the transfer function.
coherent	if TRUE, nc identical white noise time series are assumed to estimate the transfer function; else (the default) nc independent noise series.
...	additional parameters which are passed to the spectral estimation function SpecMTM.

Details

The approach is described in detail in Münch and Laepple (2018). In brief, nc Gaussian white noise time series are created and diffused and the average of these time series is calculated. The process is repeated ns times. For each of the ns realisations, spectra of the average diffused and undiffused records are calculated yielding the spectral transfer function.

Diffusion is modelled as the convolution of the undiffused record with a Gaussian with standard deviation given by the diffusion length sigma. The spectral estimates are calculated using Thomson’s multitaper method with three windows with linear detrending before analysis.

Value

a list of the components signal, diffused and ratio which are objects of class "spec" providing the averages over the ns simulations of:

signal:

the undiffused noise spectrum

diffused:

the diffused noise spectrum

ratio

their ratio (diffused/undiffused), i.e. the transfer function.

Author(s)

Thomas Münch

References

Münch, T. and Laepple, T.: What climate signal is contained in decadal- to centennial-scale isotope variations from Antarctic ice cores? Clim. Past, 14, 2053–2070, https://doi.org/10.5194/cp-14-2053-2018, 2018.

EarthSystemDiagnostics/proxysnr documentation built on Oct. 2, 2021, 3:03 p.m.