Susan Skone, University of Calgary; M. Najmafshar, University of Calgary
Keywords: Global Navigation Satellite Systems, ionosphere, space weather
Abstract:
Global Navigation Satellite System (GNSS) technologies are susceptible to space weather effects, and are rapidly evolving with multiple constellations available from Europe, the Unites States, Russia and China. Positioning, navigation and timing (PNT) accuracies are approaching the threshold of sub-centimetre globally, with a multitude of new services from precision timing to unmanned systems and drones. Integrity must now extend from traditional safety-critical navigation systems (e.g. aviation and marine) to ubiquitous autonomous platform applications and beyond. There is a growing focus to ensure that current and future GNSS services are robust and reliable during severe space weather and the associated ionospheric disturbances.
There are multiple phenomena that produce space weather impacts on GNSS: the introduction of large gradients in the ionospheric total electron content (TEC); the rapid variation of a signal’s amplitude and/or phase (scintillation); and/or the sudden increase in background L-band noise. Often such effects are reduced through dual-frequency ionosphere-free combinations, models, and/or differential techniques. Structured features in TEC and small-scale plasma irregularities are difficult to reduce or mitigate, however, and the larger PNT errors can challenge integrity of navigation solutions. For example, we have observed the storm-enhanced density phenomenon, and associated tongue of ionization at Arctic latitudes, generating ten-fold increases in GNSS positioning errors exceeding system thresholds. Scintillations in the Canadian Arctic have resulted in loss of navigation capabilities for low-cost marine receiver configurations.
The rapid development of new GNSS capabilities requires ongoing investigations and understanding by space weather researchers to quantify, predict and mitigate potential impacts on PNT integrity, accuracy and reliability. Space weather hazard strategies attempt to capture such conditions of high impact (e.g. polar patches, storm enhanced density and aurora) for system users and operators. Characterization of ionospheric phenomena resulting from space weather events is key to such studies, with knowledge of ionospheric plasma distribution translating directly into effects on GNSS transionospheric signal propagation.
In this presentation we highlight ionospheric disturbances for current and emerging GNSS applications, associated impacts, and consider the context of recent national efforts to advance space weather strategies and action plans. For example, in 2019 the United States conducted (as part of the national space weather action plan) a review of ionospheric disturbances benchmarks critical to vulnerability assessments for national infrastructure and services, and for stakeholder mitigation planning. The intention was to capture physical properties of the medium and to define several key parameters best characterizing the space environment: these included TEC, spatial/temporal variations of TEC, peak electron density, peak height of electron density, turbulence measures (scintillation), and signal absorption. All such values translate readily into impacts on existing and emerging systems. We reflect on our participation in these national efforts.
We also quantify aspects of PNT accuracy and integrity using both our real data networks and our extensive GNSS simulation tools that translate key parameters into user/operator impacts. It is critically important to ensure that these tools include state-of-the-art current and future GNSS receiver designs and navigation algorithms in order to determine extreme impacts on users. For example, the largest magnitude ionospheric propagation errors may be readily rejected as outliers with minimal user impact while smaller signal perturbations may skew navigation solutions (as they accumulate over time) beyond acceptable error bounds. Our examples include 1) ionospheric large-scale phenomena specification and structures within, both spatially and temporally, 2) small-scale irregularity specification affecting GNSS signal propagation, and 3) translating the impact of such phenomena into various user domains.
Date of Conference: September 15-18, 2020
Track: Atmospherics/Space Weather