GDopp: processing of ADV data

#'@title convert epsilon to k600
#'@description 
#'Uses Zappa et al. 2007 to convert epsilon to k600.  \cr
#'
#'@details a \code{GDopp} function for converting epsilon to k600.\cr 
#'
#'@param epsilon Turbulence dissipation rate
#'@param temperature Temperature in degC of near surface water
#'@param nu Constant of proportionality
#'@return a single k600 value
#'@keywords epsilon2k
#'@references
#'Zappa, Christopher J., Wade R. McGillis, Peter A. Raymond, James B. Edson, Eric J. Hintsa, 
#'Hendrik J. Zemmelink, John WH Dacey, and David T. Ho. 
#'\emph{Environmental turbulent mixing controls on air/water gas exchange in marine and aquatic systems.} 
#'Geophysical Research Letters 34, no. 10 (2007).
#'@examples 
#'\dontrun{
#'folder.nm <- system.file('extdata', package = 'GDopp') 
#'file.nm <- "ALQ102.dat"
#'block.use <- 7
#'data.adv <- load_adv(file.nm=file.nm, folder.nm =folder.nm)
#'window.adv <- window_adv(data.adv,freq=32,window.mins=10)
#'data.sen <- load_sen(paste0(substr(file.nm,start=1,stop=nchar(file.nm)-4),'.sen'))
#'temp.adv <- temp_calc(data.sen,window.adv$window.idx,freq=32)
#'chunk.adv <- window.adv[window.adv$window.idx==block.use, ]
#'epsilon <- fit_epsilon(chunk.adv,freq=32)
#'epsilon_to_k(epsilon,temperature=temp.adv[block.use],nu=0.2)
#'}
#'@export

epsilon_to_k <- function(epsilon,temperature=20,nu=0.2){
  
  if (length(epsilon) != length(temperature)){
    stop('input vectors for epsilon and temperature must have the same number of elements')
  }
  k.vis <- get_kin_viscosity(temperature)
  m4s4 <- 86400^4
  e.k <- epsilon*k.vis*m4s4 #now in m/day
  
  # convert to m/day
  k600 <- nu*(e.k)^0.25*600^(-0.5)
  return(k600)
}