Simulations of Radio Occultation by Using Ray Tracing Method with nonspherical symmetric atmosphere

With the advent of global positioning system (GPS), radio occultation (RO) techniques have been used to investigate planetary atmosphere and obtain the profiles of Earth’s atmospheric parameters. With the measurements of the excess phase, the atmospheric profiles of bending angle, refractivity, pressure, and temperature are able to be retrieved. In some RO researches, simulations using ray-tracing techniques are conducted by using the angles between the tangent vectors at beginning and ending points. In order to make the simulations of ray tracing more conform to the observation results, a modified ray-tracing algorithm has been developed. In the proposed algorithm, the phase path of the signal propagating in the Earth atmosphere is first simulated, and then the bending-angle profiles of the signal are retrieved. The structure of the Earth atmosphere is based on the analyses of European Centre for Medium-Range Weather Forecasts (ECMWF). And the oblateness of the Earth is also considered in the algorithm. Moreover, in order to make the ending point of signal trace match the anticipated ending point, a mechanism in the algorithm is introduced. The retrieved bending-angle profiles using the proposed algorithm will be compared with those obtained from Taiwan Analysis Center for COSMIC (TACC). Satisfactory results are obtained.