A simplified GNSS tropospheric delay model based on the nonlinear hypothesis

We have derived a global zenith tropospheric delay simplified model (GZTDS), assuming that the troposphere is a nonlinear system and can be handled as a black box. The GZTDS and its variation in time can be expressed as a series of cosine components, which represent various periods of tropospheric delay changes. Undetermined coefficients are extracted by data fitting from the mean sea level historical data of the global geodetic observing system atmosphere on a 2A degrees A x 2.5A degrees grid. A combination of our model and the Vienna Mapping Function 1 can predict slant delays for global navigation satellite system sites using the zenith angle and nearest grid coordinates as the input and generate a global slant tropospheric delay simplified model (GSTDS) and its extension. Comparisons with the zenith delays provided by the International GNSS Service at 358 sites show that the biases are between -3.36 and 2.41 cm, and the mean standard deviation is 3.46 cm for the year 2014. This result is at the same level of accuracy as the global pressure and temperature 2 wet model (GPT2w), with the GZTDS requiring no local meteorological parameters. The accuracy of GSTDS depends on the zenith angle and shows nonlinear characteristics. Several statistics of biases and standard deviations illustrate model adaptation with respect to latitude or altitude.