R/gravity_station.R

In earthtide: Parallel Implementation of 'ETERNA 3.40' for Prediction and Analysis of Earth Tides

#-------------------------------------------------------------------------------
# gravity_station
#
# \code{gravity_station} returns the estimated gravity for a latitude.
# http://the-mostly.ru/misc/local_gravity_online_calculator.html
#
# @param latitude the station latitude
# @param elevation the station elevation in meters
#
# @return gravity for location in m/s^2
#
# @keywords internal
#
#-------------------------------------------------------------------------------
gravity_station <- function(latitude, elevation) {

  to_radians <- pi / 180

  a <- 6371000
  sin_lat <- sin(latitude * to_radians)^2

  9.7803267714 * (1.0 + 0.00193185138639 * sin_lat) /
    sqrt(1.0 - 0.00669437999013 * sin_lat) *
    (1.0 + elevation / a)^(-2)

}