dplR (version 1.6.8)

powt: Power Transformation of Tree-Ring Data

Description

Perform power transformation simultaneously for a data.frame of raw tree-ring width series.

Usage

powt(rwl)

Arguments

rwl

a data.frame of raw tree-ring widths series, such as that produced by read.rwl or read.fh

Value

A data.frame containing the power transformed ring width series.

Details

This procedure is a variance stabilization technique implemented after Cook & Peters (1997): for each series a linear model is fitted on the logs of level and spread, where level is defined as the local mean \(M_t = \left(R_t + R_{t-1}\right)/2\) with ring widths R, and spread S is the local standard deviation defined as \(S_t = \left|R_t - R_{t-1}\right|\). The regression coefficient b from \(\log S = k + b \log M\) is then used for the power transform \(\star{R}_t = R_t^{1-b}\).

References

Cook, E. R. and Peters, K. (1997) Calculating unbiased tree-ring indices for the study of climatic and environmental change. The Holocene, 7(3), 361<U+2013>370.

See Also

rcs

Examples

# NOT RUN {
library(utils)
data(gp.rwl)
gp.pt <- powt(gp.rwl)
# }