Ray tracing simulation for GPS radio occultation in non-spherically symmetric atmosphere with ECMWF analysis

In this research, a ray tracing model is built up to simulate the propagation of signal in global positioning system (GPS) radio occultation (RO) mission. When GPS signal propagate through the Earth´s atmosphere, it will be bent and delayed due to the gradient atmosphere refractive index and received by low Earth orbit (LEO) satellite. Then the parameter profiles of atmosphere can be retrieved by using the received signal. In the previous research, in order to simplify the simulation, the Earth´s atmosphere is assumed as spherical symmetry and the positions of GPS and LEO satellites are not considered in simulations. In the model, the shape of the Earth is assumed as an ellipse. The information of European Centre for Medium-Range Weather Forecasts (ECMWF) is used to construct the refractive index of Earth´s atmosphere. And two aiming algorithm are developed to control the initial propagating direction of GPS signal to begin from the prescribed GPS satellite position and end at the LEO satellite position. The model is tested and verified by comparing with analytical and observational data.