R/estNv.R

In JVAdams/EchoNet2Fish: Estimate Fish Abundance from Acoustic Echoes and Net Catch

#' Estimate the Number of Targets in the Acoustic Beam
#'
#' Estimate the number of targets in the acoustic sampling volume.
#' @param c
#'   Numeric scalar, sound speed in m/sec, default 1450.
#' @param tau
#'   Numeric scalar, pulse duration in sec, default 0.0004.
#' @param psi
#'   Numeric scalar, two-way equivalent beam angle in steradians.
#' @param R
#'   Numeric vector, range to target in m.
#' @param rhov
#'   Numeric vector, volumetric fish density in number per m^3, same length as \code{R},
#'   typically the result of a call to \code{\link{estrhov}}.
#' @details
#'   The number of targets in the acoustic sampling volume
#'   is estimated according to Sawada et al. (1993) as
#'   Nv = \code{c} * \code{tau} * \code{psi} * \code{R}^2 * \code{rhov} / 2.
#' @return
#'   A numeric vector the same length as \code{R} containing the estimated
#'   number of targets in the acoustic beam.
#' @export
#' @references
#' Sawada, K., Furusawa, M., and Williamson, N.J. 1993.
#'   Conditions for the precise measurement of fish target strength in situ.
#'   Fisheries Science (Tokyo) 20:15-21.
#' @seealso
#'   \code{\link{estrhov}}
#' @examples
#' mypsi <- 0.008
#' myrange <- c(10, 20, 30)
#' myrhov <- c(0.0001, 0.01, 0.0006)
#' estNv(psi=mypsi, R=myrange, rhov=myrhov)
#'
estNv <- function(c=1450, tau=0.0004, psi, R, rhov) {
  Nv <- c * tau * psi * R^2 * rhov / 2
  return(Nv)
}