International Global Navigation Satellite Systems Society IGNSS Symposium 2011 University of New South Wales, Sydney, NSW, Australia 15 – 17 November 2011 Analysis of Zenith Path Delay in Dynamically Changing Environment Mukesh R. Vyas, Samsung Lim, Chris Rizos School of Surveying and Spatial Information Systems, The University of New South Wales. Tel: - +61-2-9385 4205 Fax: - +61-2-9313 7493 Email: - m.vyas@unsw.edu.au Website: - www.gmat.unsw.edu.au Kefei Zhang School of Mathematical and Geospatial Sciences, The RMIT University. Gregor Moeller Institute of Geodesy & Geophysics, Vienna University of Technology. ABSTRACT Many studies have been conducted for evaluating the tropospheric effect on GPS signals. Among many troposphere models, Saastamoinen’s and Neill’s models have been widely used. The troposphere’s zenith path delay in GPS signals can be estimated by the hydrostatic component of the Saastamoinen model and then the delay can be mapped with the dry Niell mapping function in order to obtain the slant path delay. This paper aims to identify and analyse the characteristics of the tropospheric delay associated with an aircraft’s flight trajectory using the aforementioned troposphere models. The test data consists of the kinematic data observed during a 700km-long flight at the maximum elevation of 3,300m and the static data observed at seven reference stations distributed across the study area. The data was processed on an epoch-by-epoch basis in the double-differenced mode with mixed, kinematic and static stations. The correlation between the delay and the flight height is addressed as a result of the analysis. Since the estimation can be affected by the data quality, the baseline length and other factors, it is necessary to cross-verify the estimation. Hence the expected accuracy of the estimation is also provided along the flight trajectory. KEYWORDS: Tropospheric effect, Zenith Path Delay, Slant Path Delay, Saastamoinen model, Niell model. 1. INTRODUCTION Global Positioning System (GPS) as well as Russia’s Global Navigation Satellite System (GLONASS) are currently operational Global Navigation Satellite Systems (GNSS) and play an important role as space-based geospatial infrastructure. GNSS provides accurate