Kinematic GNSS tropospheric estimation and mitigation over a range of altitudes

Abstract

This thesis investigates the potential for estimating tropospheric delay from Global Navigation Satellite Systems (GNSS) stations on moving platforms experiencing a change in altitude. The ability to accurately estimate tropospheric delay in kinematic GNSS positioning has implications for improved height accuracy due to the mitigation of a major GNSS error source, and for the collection of atmospheric water vapour data for meteorology and climate studies. The potential for extending current kinematic GNSS positioning estimates of tropospheric delay from sea level based studies to airborne experiments, and the achievable height accuracy from a range of tropospheric mitigation strategies used in airborne GNSS positioning, are explored. An experiment was established at the Snowdon Mountain Railway (SMR), utilising the railway to collect a repeatable kinematic dataset, profiling 950 m of the lower atmosphere over a 50 day period. GNSS stations on stable platforms and meteorological sensors were installed at the extremities of the trajectory, allowing reference tropospheric delays and coordinates to be established. The retrieval of zenith wet delay (ZWD) from kinematic GNSS solutions using tropospheric estimation strategies is validated against an interpolated reference ZWD between GNSS stations on stable platforms, together with profiles from 100 m resolution runs of the UK Met Office Unified Model. Agreement between reference ZWD values and a combined GPS+GLONASS precise point positioning (PPP) solution is demonstrated with an accuracy of 11.6 mm (RMS), similar to a relative positioning solution and previous shipborne studies. The impact on the height accuracy from estimating tropospheric delay in kinematic GNSS positioning is examined by comparing absolute and relative GNSS positioning solutions to a reference trajectory generated from a relative GNSS positioning solution ii processed with reference to the GNSS stations on stable platforms situated at the extremities of the SMR. A height accuracy with a standard deviation of 72 mm was demonstrated for the GPS+GLONASS PPP solution, similar to a GPS-only relative solution, and providing an improvement over the GPS-only PPP solution.