Real time STD calculation at low elevation by GPS

Global Positioning System (GPS) has become a powerful tool in a number of applications such as the geophysics and remote sensing. Real time slant path tropospheric delay (STD) is of benefit in near real time weather forecasting, climatologic applications, and reconstructing refractivity profile. A new method of acquiring real time STD at very low elevation (0°-5°), is presented in the paper which is based on singular ground-based GPS observations with International GPS Service (IGS) ultra-rapid product. An experiment was carried out to validate the feasibility on an island in Shantou, south China during July 2009. Results from radiosondes, GPS and mapping functions are compared. It shows that the mean error of GPS-derived STD is smaller than mapping function. Consequently, it should be feasible to obtain real time STD at low elevation (0°-5°) by GPS.