Real-time Estimation of Tropospheric Scattering Slant Delay of Low-elevation Obtained by Improved Ray Tracing

Considering the disadvantage of oblique delay estimation of tropospheric scattering at arbitrary stations, which is difficult to obtain real-time sounding meteorological data, an oblique delay estimation algorithm of tropospheric scattering based on improved ray tracing method with ground meteorological parameters is proposed. In order to get rid of the method's dependence on radiosonde data, the algorithm infers the relationship between refractive index and altitude through the formula of meteorological parameters in the model of medium latitude atmosphere. The interpolation of meteorological parameters in the model of UNB3m is used to gain the coefficient of temperature and water vapor pressure. Meteorological data for 2012 from 6 International GNSS Service (IGS) stations in Asia are selected to test the applicability of new method, the results suggest that precision is less than 1 cm. Then, the tropospheric slant delays of three parts observation stations under different angles of incidence (0 degrees similar to 5 degrees) are calculated by the modified algorithm. The results suggest that the maximum delay is 17.03 similar to 33.10 m in a single way time transfer. In two way time transfer, when the delay can counteract 95%, time delay is 2.88 similar to 5.52 ns.