Optimizing Global Navigation Satellite Systems network real-time kinematic infrastructure for homogeneous positioning performance from the perspective of tropospheric effects.

Chen Yu,Nigel T Penna,Zhenhong Li

doi:10.1098/rspa.2020.0248

Abstract

Real-time centimetre-level precise positioning from Global Navigation Satellite Systems (GNSS) is critical for activities including landslide, glacier and coastal erosion monitoring, flood modelling, precision agriculture, intelligent transport systems, autonomous vehicles and the Internet of Things. This may be achieved via the real-time kinematic (RTK) GNSS approach, which uses a single receiver and a network of continuously operating GNSS reference stations (CORS). However, existing CORS networks have often been established simply by attempting regular spacing or in clusters around cities, with little consideration of weather, climate and topography effects, which influence the GNSS tropospheric delay, a substantial GNSS positional error and which prevents homogeneous RTK accuracy attainment. Here, we develop a framework towards optimizing the design of CORS ground infrastructure, such that tropospheric delay errors reduce to 1.5 mm worth of precipitable water vapour (PWV) globally. We obtain average optimal station spacings of 52 km in local summer and 70 km in local winter, inversely related to the atmospheric PWV variation, with denser networks typically required in the tropics and in mountainous areas. We also consider local CORS network infrastructure case studies, showing how after network modification interpolated PWV errors can be reduced from around 2.7 to 1.4 mm.

Highlights

While Precise Point Positioning (PPP) does not require the direct use of continuously operating GNSS reference stations (CORS) data, the drawback is that the unknown number of carrier phase cycles between the satellite and receiver is estimated as a floating point value, and it usually takes tens of minutes for such float ambiguities to converge to the correct values and thereafter centimetre to decimetre positional accuracy to be realized [16]
Our main objective is to determine how many CORS are required over a given region, by computing the station spacing density needed for the successful interpolation of precipitable water vapour (PWV) with homogeneous accuracy, and to investigate the dependence on geographical location, topography and climate
We have proposed and developed a framework to optimize Global Navigation Satellite Systems (GNSS) CORS network infrastructure with regard to the distribution of the variations in PWV and topography, in order to facilitate centimetre-level homogeneous accuracy for Network real-time kinematic (RTK) positioning

Summary

Introduction

Real-time Global Navigation Satellite Systems (GNSS) positioning with centimetre-level precision and accuracy is commonly used and needed in utilities mapping [1], landslide monitoring [2], rapid earthquake source determination and tsunami early warning [3], coastal erosion monitoring [4], glacier and permafrost monitoring [5,6], river channel monitoring [7], precision agriculture [8,9], highway construction [10], structural monitoring [11], flood modelling [12], and photogrammetric mapping and LiDAR surveys from aeroplanes/helicopters [13] and unmanned aerial vehicles [14]. Network RTK does not require global precise satellite orbits and clocks or require the user to establish their own local GNSS reference station, but makes use of a regional network of CORS at known ground locations where observational error corrections, such as for orbits, ionospheric and tropospheric delays [18,19,20,21,22], are continuously computed and transmitted to the user’s roving receiver in real time. Our main objective is to determine how many CORS are required over a given region, by computing the station spacing density needed for the successful interpolation of PWV (and tropospheric delay) with homogeneous accuracy, and to investigate the dependence on geographical location, topography and climate Ensuring such optimal CORS network design for tropospheric delay will help enable homogeneous performance of Network RTK and subsequently its practical uptake for all of the aforementioned RTK applications and developing technologies. Scenarios for idealistic new CORS Network RTK design are considered, ranging from station spacings of 80 to 5 km (assumed to be the maximum density of a CORS network anywhere), along with case studies from selected national CORS networks illustrating how existing infrastructure can be best densified to mitigate tropospheric delay errors

Precipitable water vapour reference dataset

Interpolation of precipitable water vapour

Global optimal station spacing

Conclusion and outlook