R/DO_units_convert.R

In acgold/compensateR: Temperature and salinity compensation for water quality sensor data

#' convert dissolved oxygen from mg/L to percent saturation
#'
#'\code{DO_convert_units} accepts dissolved oxygen and temperature measurements
#'and adjusts dissolved oxygen based on solubility of oxygen at
#'different temperatures. Uses USGS methods (citing Garcia and Gordon, 1992)
#'found here: \url{https://water.usgs.gov/admin/memo/QW/qw11.03.pdf}
#'
#'@param temperature A vector or 1-D column of temperature measurements that coincide with conductivity measurements
#'@param dissolved_oxygen A vector or 1-D column of dissolved measurements that coincide with temperature measurements
#'@param salinity A vector or 1-D column of salinity measurements that coincide with temperature measurements
#'@return Dissolved oxygen values converted to percent saturation
#'@export
DO_adjust_units <- function(temperature, dissolved_oxygen, salinity = rep(0, length(temperature))){
  t <- c(temperature)
  d <- c(dissolved_oxygen)

  if(length(t) != length(d)){
    return("Lengths do not match!")
  }

  adj_t <- log((298.15 - t)/(273.15 + t))

  adj_DO <- 1.42905 * exp(2.00907 + (3.22014*adj_t) + (4.05010*adj_t^2) + (4.94457*adj_t^3) - (0.256847*adj_t^4) + (3.88767*adj_t^5))

  salinity_factor <- exp((-0.00624523 - 0.00737614* adj_t - 0.0103410*adj_t^2 - 0.00817083*adj_t^3) * salinity - 4.88682*10^-7*salinity^2)

  final_DO <- 100* (d/(adj_DO*salinity_factor))

  return(final_DO)

}