Estimating the Residual Tropospheric Delay for Airborne Differential GPS Positioning (A Summary)

When post-processing dual frequency carrier phase data, the residual tropospheric delay can easily be the largest remaining error source. This error can contribute a bias in height of several centimetres even if simultaneously recorded meteorological data are used. This is primarily due to the poor representation of the water vapour profile in the tropospheric delay models. In addition, a lack of real-time meteorological data would force the scaling of either surface values or standard atmosphere values; these are also unlikely to accurately represent the ambient atmosphere.To obtain the highest precision in kinematic GPS some advantage may be obtained by estimating this error source along with the position solution. The simple tests reported in this paper removed biases of several centimetres in height when estimating the residual tropospheric delay from GPS data recorded at an aircraft in flight. However, important limitations exist in the geometry of the satellite coverage which must be considered before the full reliability of the technique can be quantified.