Fitting a model to the gas concentration curve and estimating the slope over time, using the HM model (Pedersen et al., 2010; Hutchinson and Mosier, 1981).

Fits the exponential expression to the concentration evolution C(t) = C_m + (C_z - C_m) exp(-b * t)

Usage

flux_fitting_hm(
  conc_df_cut,
  conc_df,
  conc_col,
  f_start,
  f_fluxid,
  start_cut,
  cz_window,
  b_window,
  roll_width,
  t_zero
)

Arguments

conc_df_cut

dataframe of gas concentration over time, cut

conc_df

dataframe of gas concentration over time

conc_col

column with gas concentration

f_start

column with datetime when the measurement started

f_fluxid

column with ID of each flux

start_cut

time to discard at the start of the measurements (in seconds)

cz_window

window used to calculate Cz, at the beginning of cut window

b_window

window to estimate b. It is an interval after tz where it is assumed that C fits the data perfectly

roll_width

width of the rolling mean for CO2 when looking for tz, ideally same as cz_window

t_zero

time at which the slope should be calculated (for quadratic fit)

Value

a dataframe with the slope at t zero, modeled concentration over time and exponential expression parameters

References

Pedersen, A.R., Petersen, S.O., Schelde, K., 2010. A comprehensive approach to soil-atmosphere trace-gas flux estimation with static chambers. European Journal of Soil Science 61, 888–902. https://doi.org/10.1111/j.1365-2389.2010.01291.x

Hutchinson, G.L., Mosier, A.R., 1981. Improved Soil Cover Method for Field Measurement of Nitrous Oxide Fluxes. Soil Science Society of America Journal 45, 311–316. https://doi.org/10.2136/sssaj1981.03615995004500020017x