Improved Modelling of Short and Long Term Characteristics of Ionospheric Disturbances
Acronym:SCIONAV
Code:IONO-OE-TN-2015-003
Funder:European Space Agency
Start date:2015 November 2nd
End date:2017 July 15th
Keywords:Navigation, GPS, GNSS, Ionospheric Disturbances
SPCOM Participants:Gregori Vázquez Grau
SPCOM Responsible:Jaume Riba Sagarra

Summary

This project aims at improving the understanding of the Ionospheric processes during high solar activity periods, when the disturbances of the Ionosphere are more severe, and how they impact the performance of Global Navigation Satellite Systems (GNSS). The majority of the effects affecting Ionosphere behaviour are well understood, as well as their periodicity and dependencies. The Sun activity exhibits a long-term variation following approximately an 11-year cycle, and ESA has now gathered data during the previous and the current solar maximum, having very probably registered abnormal effects impacting GNSS systems. This data collection exercise was done in the scope of the ESA Monitor project, under the European GNSS Evolutions Programme, and its data will be available as a starting point for this study. During periods of high solar activity the Ionospheric conditions can vary rapidily and in a very localised way.

The majority of these perturbation fall in the definition of Scintillation, defined as rapid fluctuations of amplitude and/or phase of the radio wave signal, respectively, caused by small-scale irregularities, which modify the ionospheric refractive index. Strong scintillations can induce cycle slips and loss-of-lock in GNSS receivers on one or more signals simultaneously and they can affect GNSS in different ways: the user receivers can lose some of the GNSS signals, and the ground stations can lose one frequency or several frequencies. Other ionospheric spatial and temporal (small-scale) disturbances during high solar activity or during storms (perturbed conditions), including bubbles, depletions, etc... also affect the navigation performance of GNSS receivers, since they affect the estimation of the overall Ionospheric delay. This study will also focus on improving the models for these disturbances occurring at lower frequency but still at small scale.

Finally, the mapping functions most frequently used to compute Slant TEC (Total Electron Content) from Vertical TEC assume that the electrons are concentrated in a single shell, close to the atmospheric layer with the hightest elctron density. While this is accurate enough for periods of relatively low solar activity, they can produce large errors during perturbed conditions. This study will also aim at improving existing mapping functions with a more robust model, able to accurately reflect and predict conditions in periods of high solar activity.





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