Ray tracing simulation in nonspherically symmetric atmosphere for GPS radio occultation

Wen Hao Yeh, Cheng Yung Huang, Tsen Chieh Chiu, Ming Quey Chen, Jann Yenq Liu, Yuei An Liou

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


A three-dimensional ray tracing model with aiming algorithms for global positioning system (GPS) signal is proposed to make simulations conform to the realistic radio occultation (RO) signal propagation. The two aiming algorithms used in this study ensure the initial and end point ray trajectories are located in the prescribed region. In past studies, the ray tracing techniques applied to the RO signal simulation usually assumed a spherically symmetrical atmosphere for simplicity. The exact GPS and low earth orbit (LEO) satellite locations are not considered in the simulation. These two assumptions make the simulation unrealistic for GPS signal propagation in the RO technique. In the proposed model, the shape of the earth is assumed as an ellipse. The information from European Centre for Medium-Range Weather Forecasts (ECMWF) analysis is used to setup the atmosphere in the simulation. Two aiming algorithms are developed to determine the initial signal propagating direction to make the simulated signal start from the prescribed GPS satellite position and end in the close vicinity of the LEO satellite position. An ideal spherical symmetric atmospheric structure is used to verify the ray tracing model. The fractional difference between real and simulated refractivity results is less than 0.1%. Otherwise, the GPS and LEO satellite position in the Formosat-3/COSMIC observation and the ECMWF analysis, considering the earth's flattening, is also used to verify the aiming algorithms. All of the simulated signals end in close vicinity to the LEO satellite position in the simulation results.

Original languageEnglish
Pages (from-to)801-812
Number of pages12
JournalTerrestrial, Atmospheric and Oceanic Sciences
Issue number6
StatePublished - 1 Dec 2014


  • Radio occultation
  • Ray tracing


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