R/length_to_breadth_at_time.r

In nrcan-cfs-fire/cffdrs: Canadian Forest Fire Danger Rating System

#' Length-to-Breadth ratio at time t
#'
#' @description Computes the Length to Breadth ratio of an elliptically shaped
#' fire at elapsed time since ignition. Equations are from listed FCFDG (1992)
#' and Wotton et. al. (2009), and are marked as such.
#'
#' All variables names are laid out in the same manner as Forestry Canada
#' Fire Danger Group (FCFDG) (1992). Development and Structure of the
#' Canadian Forest Fire Behavior Prediction System." Technical Report
#' ST-X-3, Forestry Canada, Ottawa, Ontario.
#'
#' Wotton, B.M., Alexander, M.E., Taylor, S.W. 2009. Updates and revisions to
#' the 1992 Canadian forest fire behavior prediction system. Nat. Resour.
#' Can., Can. For. Serv., Great Lakes For. Cent., Sault Ste. Marie, Ontario,
#' Canada. Information Report GLC-X-10, 45p.
#'
#' @param FUELTYPE The Fire Behaviour Prediction FuelType
#' @param  LB: Length to Breadth ratio
#' @param HR: Time since ignition (hours)
#' @param CFB: Crown Fraction Burned
#'
#' @returns Length to Breadth ratio at time since ignition
#'
#' @noRd

length_to_breadth_at_time <- function(FUELTYPE, LB, HR, CFB) {
  # Eq. 72 (FCFDG 1992) - alpha constant value, dependent on fuel type
  alpha <- ifelse(
    FUELTYPE %in% c("C1", "O1A", "O1B", "S1", "S2", "S3", "D1"),
    0.115,
    0.115 - 18.8 * (CFB**2.5) * exp(-8 * CFB)
  )
  # Eq. 81 (Wotton et.al. 2009) - LB at time since ignition
  LBt <- (LB - 1) * (1 - exp(-alpha * HR)) + 1
  return(LBt)
}

.LBtcalc <- function(...) {
  .Deprecated("length_to_breadth_at_time")
  return(length_to_breadth_at_time(...))
}