raw_sdr {spatialwarnings}

Spectral Density Ratio (SDR) indicator

Description

Compute the ratio of low frequencies over high frequencies of the r-spectrum.

Usage

raw_sdr(mat, sdr_low_range = NULL, sdr_high_range = NULL)

Arguments

mat

A matrix with continuous values, or a logical matrix (TRUE/FALSE).

sdr_low_range

The range of values (in proportion) to use for the computation of the spectral density ratio. For example, for the lowest 20% (default value), set sdr_low_range to c(0, .2).

sdr_high_range

The range of values (in proportion) to use for the computation of the spectral density ratio. For example, for the highest 20% (default value), set sdr_high_range to c(.8, 1).

Details

SDR measures the increase in long-range correlations before a critical point. It is the ratio of the average low frequency value over high frequency values. In this implementation, an increase in SDR implies a "reddening" of the r-spectrum. See also spectral_sews for a more complete description.

Low and high frequencies are averaged in order to compute the SDR. The parameters sdr_low_range and sdr_high_range control which frequencies are selected for averaging. For example sdr_low_range = c(0, .2) (default) uses the lower 20 the average of low frequencies. sdr_high_range = c(.8, 1) uses the higher 20

Value

The SDR values computed on the matrix as a named vector

References

Carpenter, S.R. & Brock, W.A. (2010). Early warnings of regime shifts in spatial dynamics using the discrete Fourier transform. Ecosphere

See Also

indictest, rspectrum, plot_spectrum, spectral_sews, extract_spectrum

Examples

## Not run:  
data(serengeti)
serengeti.sdr <- raw_sdr(serengeti[[1]], 
                         sdr_low_range = c(0, 0.2), 
                         sdr_high_range = c(0.8, 1))
compute_indicator(serengeti, raw_sdr)

## End(Not run)