Establishment of a new global model for zenith tropospheric delay based on functional expression for its vertical profile

The tropospheric delay is one of the most significant error sources for radio navigation and space geodetic techniques. Its value is seriously affected by the height of the observing object. Due to the requirement of real-time capability and the drastic variations in the height of the object, there are various defects in existing tropospheric delay models for calculating the delay in kinematic navigation and positioning. Based on the vertical profiles of zenith tropospheric delay (ZTD) derived from ERA-Interim reanalysis data in 2005 and 2006, as well as it's hydrostatic and non-hydrostatic components (ZHD and ZWD), the optimal fitting method of ZTD with respect to height was studied and a new global ZTD model which is referred to as SHAG-H was established. The SHAG-H model is built on the variation of water vapor in the vertical atmosphere and represents ZTD as a piecewise function of height. Then the variations of parameters in each function with respect to time are modeled. The most of mean bias between the SHAO-H ZTD and the integral ZTD at different isobaric layers are within +/- 1 mm, while the RMS reduces from 39 mm to less than 1 mm with the increase of height. Compared with International GNSS Service (IGS) ZTD at 117 global stations in 2011, the SHAO-H model (the bias is 7.02 mm, the RMS is 38.50 mm) is superior to the UNB3m model (the bias is 14.67 mm, the RMS is 51.95 mm). The SHAO-H model we constructed has many advantages such as consistency in accuracy and simplicity in computation, which is suitable for the users at arbitrary height in the neutral atmosphere.