An Improved Global Zenith Tropospheric Delay Model

The time resolution of GZTD model developed by Yao[16] is 24 hours. To further improve the time resolution of GZTD model, we used the time series of global 4D-grid ZTD from 2002 to 2009, provided by GGOS atmosphere, to construct model according to the 6 hours resolution, and then calculated the ZTD at any time using the cubic spline interpolation method. Thus we developed an improved higher time resolution (6h) GZTD model (GZTD-6h). Analyzing the inner coincidence of two models comparatively, we found that GZTD-6h model (bias: 0.17 cm, RMS: 3.9 cm) performs better than GZTD model (bias: 0.17 cm, RMS: 4.4 cm). Using ZTD time series from global International GNSS Service (IGS) sites to analyze outer coincidence, the statistical results shows that GZTD-6h model (bias:-0.22 cm, RMS: 4.05 cm) improves significantly, compared with GZTD model (bias:-0.45 cm, RMS: 4.51 cm)