Abstract
Abstract. The zenith tropospheric delay (ZTD) is an important atmospheric parameter in the wide application of global navigation satellite systems (GNSS) technology in geoscience. Given that the temporal resolution of the current global zenith tropospheric delay model (GZTD) is only 24 h, an improved model, GZTD2, has been developed by taking the diurnal variations into consideration and modifying the model expansion function. The data set used to establish this model is the global ZTD grid data provided by Global Geodetic Observing System (GGOS) Atmosphere spanning from 2002 to 2009. We validated the proposed model with respect to ZTD grid data from GGOS Atmosphere, which was not involved in modeling, as well as International GNSS Service (IGS) tropospheric product. The obtained results of ZTD grid data show that the global average bias and root mean square (rms) for the GZTD2 model are 0.2 and 3.8 cm, respectively. The global average bias is comparable to that of the GZTD model, but the global average rms is improved by 3 mm. The bias and rms are far better than the EGNOS model and the UNB series models. The testing results from global IGS tropospheric product show the bias and rms (−0.3 and 3.9 cm) of the GZTD2 model are superior to that of GZTD (−0.3 and 4.2 cm), suggesting higher accuracy and reliability compared to the EGNOS model, as well as the UNB series models.
Highlights
Radio space-based geodesy techniques suffer from atmosphere propagation delays, of which the ionospheric delay can be largely eliminated by iono-free, carrier-phase combination techniques (Spilker, 1980), and the tropospheric delay becomes the main error source
In this paper, using the time series data of global tropospheric zenith delays provided by Global Geodetic Observing System (GGOS) Atmosphere, we analyzed the diurnal variation in the zenith tropospheric delay (ZTD) which is neglected in the previous global zenith tropospheric delay model (GZTD) model, we modified the model function to develop an improved model named GZTD2
We conducted external validation testing with GGOS ZTD grid data which were not involved in modeling, and with International GNSS Service (IGS) tropospheric product
Summary
Radio space-based geodesy techniques suffer from atmosphere propagation delays, of which the ionospheric delay can be largely eliminated by iono-free, carrier-phase combination techniques (Spilker, 1980), and the tropospheric delay becomes the main error source. Krueger (2004, 2005) and Schüler (2014) obtained the annual and diurnal coefficients for underlying parameters by fitting every grid point’s meteorological parameters’ time series of the National Centers for Environmental Prediction (NCEP) atmospheric data, and established two global tropospheric delay models – TropGrid and TropGrid. On the basis of the GZTD model, and by taking the diurnal variations into consideration and modifying the expansion function, we developed an improved global non-meteorological parameters ZTD model – GZTD2. Using ZTD grid data obtained from GGOS Atmosphere and tropospheric product (Byun et al, 2009) provided by IGS for model validation, the accuracy of the GZTD2 model is superior to that of the GZTD model, and this model performs much better than other commonly used models such as the EGNOS model and UNB series models
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