IGGtropSH and IGGtroprH: Two Improved Empirical Tropospheric Delay Models Based on Vertical Reduction Functions

IGGtrop_SH and IGGtrop_rH are two improved tropospheric delay models that are established based on empirical vertical reduction functions and capable of providing zenith tropospheric delay (ZTD) correction for radio space geodetic analysis without meteorological measurements. The vertical dependence of ZTD mean values is represented by an exponential function (four coefficients in the high latitudes and six coefficients in other regions) and the vertical dependence of ZTD seasonal variation amplitudes is represented by a fifth degree polynomial. IGGtrop_SH considers both annual and semiannual variations of ZTD, while IGGtrop_rH only considers the annual variation of ZTD, which is suitable for applications more concerned about time and data storage space. The new models are validated by international Global Navigation Satellite System service tropospheric products at 292 globally distributed tracking stations between January 2010 and December 2013. The average bias values over the four years are around −0.46 cm for both models; the globally averaged root-mean-square error of IGGtrop_SH is about 3.86 cm and the value of IGGtrop_rH is about 3.97 cm. Comparison between IGGtrop_SH and the previous IGGtrop model suggests that the inclusion of semiannual variation leads to an apparent improvement of ZTD correction performance in the Northern Hemisphere, especially for middle latitudes, while no obvious change is seen in the Southern Hemisphere.