Skip to contents

Fixed-weight astronomical target spectrum (Fixed-target COCO)

Source: R/coco_target_fixed.R
coco_target_fixed.Rd

Builds the fixed-relative-weight astronomical target used by Acycle's Fixed-target COCO: nine (or other) orbital sine terms with the historical amplitudes 1.0 (eccentricity), 0.8 (obliquity) and 0.6 (precession) (cocoFixedTargetWeights.m), sampled on the data grid mapped to time at sedimentation rate sr, linearly detrended, and turned into a rectangular-window periodogram of length max(pad, n) that is linearly interpolated at the requested temporal frequencies (0 outside the target band). Unlike the adaptive target, the amplitudes never depend on the data spectrum. Translated from Acycle v3.1 freq2targetFixed.m and cocoFixedTargetWeights.m (Mingsong Li).

Usage

coco_target_fixed(
  data = NULL,
  pad = 5000,
  orbit9 = c(405.6912, 130.6979, 123.8532, 98.8517, 94.8856, 40.9897, 23.682, 22.3758,
    18.9519),
  freq = NULL,
  sr = NULL
)

Arguments

data

Record whose sampling grid the target is synthesised on (matrix or data frame; only the depth column 1, in metres, is used): the target has as many samples as data, at the median depth spacing converted to time with sr. NULL (or sr=NULL) uses 5 * max(orbit9) samples spaced 1 kyr apart. Default=NULL.

pad

Length (number of points) of the zero-padded periodogram of the target (integer, > 0; at least the number of samples is used); a larger value gives a finer frequency grid. NULL or invalid values are replaced by 5000. Default=5000.

orbit9

Astronomical periods of the target sinusoids, in kyr (numeric vector, > 0; usually nine values); their amplitudes are fixed by coco_fixed_target_weights (1.0 eccentricity, 0.8 obliquity, 0.6 precession). The default is the present-day set. Default=c(405.6912, 130.6979, 123.8532, 98.8517, 94.8856, 40.9897, 23.6820, 22.3758, 18.9519).

freq

Frequencies at which the target power is returned, in cycles/kyr (numeric vector); values outside the periodogram grid get 0. NULL returns an empty vector. Default=NULL.

sr

Sedimentation rate used to convert the depth grid of data to time, in cm/kyr (single numeric value, > 0); NULL uses the 1-kyr grid described under data. Default=NULL.

Value

Numeric vector of target power at freq.

References

Li, M., Kump, L.R., Hinnov, L.A., Mann, M.E., 2018. Tracking variable sedimentation rates and astronomical forcing in Phanerozoic paleoclimate proxy series with evolutionary correlation coefficients and hypothesis testing. Earth and Planetary Science Letters 501, 165-179.

Author

Michiel Arts (R translation); original MATLAB code: Mingsong Li

Examples

# \donttest{
depth <- seq(0, 20, by = 0.05)
f <- seq(0, 0.06, by = 0.0005)
la <- coco_target_fixed(cbind(depth, 0), pad = 5000, freq = f, sr = 5)
plot(f, la, type = "l", xlab = "Frequency (cycles/kyr)", ylab = "Power")

# }