`calc_dtmax_dr()` calculates the time series of dTmax (the maximum temperature difference between sap flow probes under zero-flow conditions) using the double regression method.
calc_dtmax_dr(
vctr_time_daily = NULL,
vctr_dtmax_pd = NULL,
wndw_size_dtmax = 11,
min_n_wndw_dtmax = 3,
output_daily = FALSE,
vctr_time = NULL,
vctr_dt = NULL,
vctr_radi = NULL,
thres_radi = 100,
thres_hour_pd = 8
)A data frame with columns below:
* The first column, `time`, gives the timestamp of the measurements. If `output_daily` is `FALSE` (default), this column is the same as the input timestamp, `vctr_time`. If `output_daily` is `TRUE`, the timestamp in daily steps is returned.
* The second column, `dt`, gives the input dT (the temperature difference between sap flow probes, degrees Celsius) time series. If `output_daily` is `TRUE`, dT is returned in daily steps. If `output_daily` is `FALSE` (default), this column is not output.
* The third column, `dtmax_dr`, gives the estimated dTmax by the double regression method. If `output_daily` is `FALSE` (default), this column has the same time step as the input timestamp. If `output_daily` is `TRUE`, the dTmax is returned in daily steps.
A timestamp vector of class POSIXct or POSIXt in daily steps. This vector indicates the start and end dates of the measurement, and is assumed to be output from the `calc_dtmax_pd()` function. The timestamps must be equally spaced and arranged chronologically. If this argument is `NULL` (default), `vctr_time`, `vctr_dt`, and `vctr_radi` must be provided to conduct the daily predawn method previously.
A vector of dTmax estimated by the daily predawn method in daily steps. This vector is assumed to be output from the `calc_dtmax_pd()` function. The length of the vector must match that of the `vctr_time_daily`. If this argument is `NULL` (default), `vctr_time`, `vctr_dt`, and `vctr_radi` must be provided to conduct the daily predawn method previously.
A positive integer indicating the window size (days) for determining moving window maximum values of dTmax. Default is 11 (days).
A positive integer indicating the minimum number of data points for calculating statistics using a moving window (default is 3). If the number of data points is less than this threshold, the statistics are not calculated in the window.
A boolean. If `TRUE`, returns dTmax time series in daily steps; else, returns dTmax in the original time steps. Default is `FALSE`.
Only valid when `vctr_dtmax_pd` is `NULL`. A timestamp vector of class POSIXct or POSIXt. This vector indicates the timings of the end of each measurement in local time. Any interval (typically 15 to 60 min) is allowed, but the timestamps must be equally spaced and arranged chronologically. Default is `NULL`.
Only valid when `vctr_dtmax_pd` is `NULL`. A vector of dT (the temperature difference between sap flow probes, in degrees Celsius) time series. The length of the vector must match that of the `vctr_time`. Missing values must be gap-filled previously. Default is `NULL`.
Only valid when `vctr_dtmax_pd` is `NULL`. A vector of global solar radiation or a similar radiative variable time series. The length of the vector must match that of the `vctr_time`. Missing values must be gap-filled previously. The unit of the time series must match that of `thres_radi`. Default is `NULL`.
A threshold value of the radiation to define daytime. Default is 100 (W m-2). The data points with radiation values above the threshold are considered daytime values. The unit of the threshold must match that of the input radiation time series.
An integer from 0 to 23. The threshold hour of the day which defines the end of predawn in local time (default is 8).
Yoshiaki Hata
The double regression method is one of the methods for determining dTmax. This method first calculates the moving window mean value of dTmax, estimated by the daily predawn method, with an eleven-day length. The dTmax that is lower than the mean is omitted, and then the moving window mean is recalculated as the final dTmax. See more details in Peters et al. (2018; New Phytologist).
`calc_dtmax`, `calc_dtmax_sp`, `calc_dtmax_pd`, `calc_dtmax_mw`, `calc_dtmax_ed`