Browsing by Author "Banville, Simon"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- ItemOpen AccessEvaluation of Kinematic GNSS PPP for Tropospheric Zenith Wet Delay Estimation in Mountainous Regions(2021-08-31) Gratton, Paul Thomas; O'Keefe, Kyle; Lachapelle, Gérard; O'Keefe, Kyle; Lachapelle, Gérard; Banville, Simon; Gao, YangIn this research, the effectiveness of kinematic zenith wet delay (ZWD) estimation using global navigation satellite systems (GNSS) precise point positioning (PPP) techniques is evaluated. The major challenges of kinematic ZWD estimation compared to static mode are (1) significant and variable GNSS signal obstruction, (2) trajectory durations of several hours compared to several days in static mode and (3) strong correlation between ZWD and height estimates. High-end and low-cost receivers are tested on vehicular highway trajectories through mountainous regions with height changes over 1000 m and varying levels of GNSS obstruction. Results are compared to static tests with open-sky conditions. Static agreement of ZWD profiles of high-end receivers was found to be at the sub-millimetre level. Agreement of low-cost receivers when using a high-grade antenna was found to be at the level of 3 mm or better. Low-cost receivers using low-cost antennas suffered ZWD biases of 3 cm due to height biases of 7-10 cm. Kinematic accuracy of ZWD profiles for high-end receivers in trajectories with minimal obstruction was found to be 5 mm, increasing to 10 mm in trajectories with more obstruction and 25 mm in very harsh obstructions. Accuracy of ZWD profiles for low-end receivers ranged from 8-20 mm in open conditions and 20-35 mm in more challenging conditions. Low-cost receivers were not tested in very harsh obstructions. Empirical ZWD models were found to agree with high-end receiver PPP-derived ZWD profiles within 15 mm or better, hence accuracy poorer than 15 mm appears ineffective.
- ItemOpen AccessKinematic Zenith Tropospheric Delay Estimation with GNSS PPP in Mountainous Areas(MDPI, 2021-08-25) Gratton, Paul; Banville, Simon; Lachapelle, Gérard; O’Keefe, KyleThe use of global navigation satellite systems (GNSS) precise point positioning (PPP) to estimate zenith tropospheric delay (ZTD) profiles in kinematic vehicular mode in mountainous areas is investigated. Car-mounted multi-constellation GNSS receivers are employed. The Natural Resources Canada Canadian Spatial Reference System PPP (CSRS-PPP) online service that currently processes dual-frequency global positioning system (GPS) and Global’naya Navigatsionnaya Sputnikovaya Sistema (GLONASS) measurements and is now capable of GPS integer ambiguity resolution is used. An offline version that can process the above and Galileo measurements simultaneously, including Galileo integer ambiguity resolution is also tested to evaluate the advantage of three constellations. A multi-day static data set observed under open sky is first tested to determine performance under ideal conditions. Two long road profile tests conducted in kinematic mode are then analyzed to assess the capability of the approach. The challenges of ZTD kinematic profiling are numerous, namely shorter data sets, signal shading due to topography and forests of conifers along roads, and frequent losses of phase lock requiring numerous but not always successful integer ambiguity re-initialization. ZTD profiles are therefore often only available with float ambiguities, reducing system observability. Occasional total interruption of measurement availability results in profile discontinuities. CSRS-PPP outputs separately the zenith hydrostatic or dry delay (ZHD) and water vapour content or zenith wet delay (ZWD). The two delays are analyzed separately, with emphasis on the more unpredictable and highly variable ZWD, especially in mountainous areas. The estimated delays are compared with the Vienna Mapping Function 1 (VMF1), which proves to be highly effective to model the large-scale profile variations in the Canadian Rockies, the main contribution of GNSS PPP being the estimation of higher frequency ZWD components. Of the many conclusions drawn from the field experiments, it is estimated that kinematic profiles are generally determined with accuracy of 10 to 20 mm, depending on the signal harshness of the environment.
- ItemOpen AccessPeer PPP-RTK: toward an affordable real-time high accuracy service(2022-12-16) Capua, Roberto; O'Keefe, Kyle; Lachapelle, Gerard Jules; Banville, Simon; Broumandam, Ali; Lichti, Derek; dos Santos, Marcelo CarvalhoThe objective of this thesis is to develop, test and analyze the performance of a high accuracy GNSS PPP-RTK (Precise Point Positioning- Real Time Kinematic) operational framework based on a dense network of peer users, through the exchange of precise Ionospheric and Tropospheric estimates between peers. The PPP-AR (PPP Ambiguity Resolution) technique, based on the use of precise satellite orbit and clocks, needs satellite biases estimates provided to receivers by external sources. It also usually requires a long convergence time for fixing carrier phase ambiguities to their correct integer values. The novel approach developed herein reduces convergence time in a network of closely spaced (on the order of a few km or less) user receivers performing PPP-RTK with the addition of sharing precise STEC (Slant Total Electron Content) and ZTD (Zenith Tropospheric Delay) estimates. These are applied by the users as constraints for faster convergence to sub-decimetre accuracies. This approach is named Peer PPP-RTK. Peer solutions are processed through a decentralized Federated Kalman Filter approach, where all peers are considered as independent local filters, deriving autonomously their own federated solutions and integrating closer peer ionospheric and tropospheric estimations. The resulting processing engine is tested first through simulations and then in a real GNSS network of permanent reference stations densified through VRS (Virtual Reference Station) representing kinematic users. A performance analysis to assess the impact of network receiver spacing with different scales of ad-hoc networks is carried out in order to simulate possible application scenarios (e.g. cadastral surveying, car information sharing and crowdsourcing in a Collaborative – Intelligent Transportation System perspective). To evaluate the performance of a dense network of peers in a city, a Monte Carlo simulation over 500 randomly distributed networks and different application scenarios is carried out and convergence time statistics are derived through Minimum Spanning Tree analysis. Analysis of these tests shows a percentage convergence time improvement of the Peer PPP-RTK approach with respect to the PPP-AR case for a network of 50 close peers in an area of 100 km2 of 37% (in harsh scenarios with high shadowing and relevant convergence time increase) to 43% (in nominal scenario with nominal PPP-AR convergence times), while preserving an accuracy of at least 5 cm after convergence. This is a highly significant improvement as it has the potential to result in minor operating costs for scores of applications. The PPP-RTK collaborative approach paves the way for the development of a Global PPP-RTK development for a host of large scale applications while reducing the number of Reference Stations required and associated infrastructure costs.