Atmospheric loading corrections applied to GPS data at the observation level

Space-geodetic techniques can detect elastic deformation of the Earth caused by atmospheric pressure loading (ATML). However, it has not yet been demonstrated whether these surface displacements should be accounted for at the time of reduction of the observations or by applying time-averaged values to the coordinates after the analysis of the observations. An analysis of the power spectral density of the ATML predicted vertical deformation shows that, aside from the diurnal and semi-diurnal periods, there is very little power in the sub-daily frequencies. The present tidal ATML models improve the analysis at sites near the equator but seem to degrade the height estimates elsewhere. The majority of the non-tidal deformation can be modelled by applying a daily-averaged correction to daily estimates of coordinates but a greater improvement in height RMS is found if non-tidal ATML is applied at the observation level.