Estimate slope/intercept of water isotope calibration regression

Performs regression between measured and known carbon isotope and mole fractions to generate a transfer function and associated uncertainty estimates using both 5-fold and leave-one-out cross-validation methods. Regression occurs on d18O and d2H values.

Usage

fit_water_regression(
  ref_data,
  calibration_half_width,
  slope_tolerance,
  r2_thres,
  plot_regression_data = FALSE,
  plot_dir = "/dev/null",
  site,
  min_nobs = NA
)

Arguments

ref_data: Reference data.frame from which to estimate calibration parameters.
calibration_half_width: Determines the period (in days) from which reference data are selected (period is 2*calibration_half_width).
slope_tolerance: Allows for filtering of slopes that deviate from 1 by slope_tolerance.
r2_thres: What is the minimum r2 value permitted in a 'useful' calibration relationship.
plot_regression_data: True or false - should we plot the data used in the regression? Useful for debugging.
plot_dir: If plot_regression_data is true, where should the plots be saved?
site: Needed for regression plots.
min_nobs: Minimum number of high-frequency observations to define a peak.

Value

Returns a data.frame of calibration parameters. Output data.frame includes slope, intercept, and r^2 values for d13C and CO2 values.