R: Power Transformation of Tree-Ring Data

powt {dplR} | R Documentation

## 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`

### 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 = (R_t + R_(t-1))/2 with ring widths R, and spread S is the local standard deviation defined as S_t = |R_t - R_(t-1)|. The regression coefficient b from log S = k + b log M is then used for the power transform R*_t = R_t^(1-b).

### Value

An object of class `c("rwl", "data.frame")` containing the power transformed ring width series with the series in columns and the years as rows. The series IDs are the column names and the years are the row names.

### Author(s)

Christian Zang. Patched and improved by Mikko Korpela.

### 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), 361–370.

### See Also

`rcs`

### Examples

    library(utils)
    data(gp.rwl)
    gp.pt <- powt(gp.rwl)
    hist(summary(gp.rwl)$skew)
    hist(summary(gp.pt)$skew)

[Package dplR version 1.7.1 Index]