A web-based package for ray tracing the neutral atmosphere radiometric path delay

An online ray-tracing package has been developed to provide zenith and slant neutral atmosphere delays using RAdiosonde OBservation (RAOB) and numerical weather prediction (NWP) models to users worldwide to assist precise global navigation satellite systems positioning scenarios. The package includes a web interface, necessary scripts to access RAOB and NWP data, and ray-tracing software capable of using both types of data. In addition, global maps of zenith hydrostatic delay, zenith non-hydrostatic or wet delay, north–south, east–west and total gradient and comparison maps of the University of New Brunswick climate-based models, and values calculated from NWP models every 3 h are also provided.In this paper, the theoretical aspects of ray tracing will be reviewed. The structure of the software and web page, validation of results using different data sources, and further development for gradient calculations are explained.