detrendfield <- function(array3d,smooth=F,...){

  # Description:
  #
  #   Removes time trend at each grid point of a three-dimensional array of data
  #   with first two space dimensions (e.g. longitude and latitude) and 
  #   third time dimension
  #
  # Usage:
  #
  #   detrendfield(array3d,smooth=FALSE,...)
  #
  # Arguments:
  #
  #   array3d: a three-dimensional array, with first two space dimensions (e.g. 
  #            longitude and latitude) and third time dimension
  #
  #   smooth: Logical. If FALSE (the default) removes linear time trend by 
  #           fitting ordinary least squares regression at each grid. If TRUE, 
  #           then time trend is removed by fitting a local weighted regression
  #           (lowess) at each grid point
  #
  #   ...:    Additional arguments passed to lowess
  #
  # Value:
  # 
  #   Three-dimensional array with the detrended data.
  #
  # Author:
  #
  #   Caio Coelho <c.a.d.s.coelho@reading.ac.uk> 9 Jan 2006
  # 
  # Examples:
  #
  #      x <- seq(-20, 20, 5)
  #      y <- seq(30, 60, 5)
  #      dim <- c(length(x), length(y), 100)
  #      data <- array(rnorm(prod(dim),25,2), dim)
  #      detrendfield(data)
  #      detrendfield(data,smooth=TRUE)
  #      detrendfield(data,smooth=TRUE,f=1/3)
  

aperm(apply(array3d, c(1,2), detrend,smooth,...),c(2,3,1))

}