Abstract
The objective of this article is to present a concept for single-frequency Global Navigation Satellite System (GNSS) positioning local ionospheric mitigation over a certain area. This concept is based on input parameters driving the NeQuick-G algorithm (the ionospheric single-frequency GNSS correction algorithm adopted by Galileo GNSS system), estimated on a local as opposed to a global scale, from ionospheric characteristics measured by a digital ionosonde and a collocated dual-frequency Total Electron Content (TEC) monitor. This approach facilitates the local adjustment of Committee Consultative for Ionospheric Radiowave propagation (CCIR) files and the Az ionization level, which control the ionospheric electron density profile in NeQuick-G, therefore enabling better estimation of positioning errors under quiet geomagnetic conditions. This novel concept for local ionospheric positioning error mitigation may be adopted at any location where ionospheric characteristics foF2 and M(3000)F2 can be measured, as a means to enhance the accuracy of single-frequency positioning applications based on the NeQuick-G algorithm.
Highlights
The performance of a Global Navigation Satellite System (GNSS) system which provides three-dimensional position with global coverage is defined by the level of accuracy of the calculated position
In the frames of real-time correction, the ionospheric effect may be partially removed using certain complex techniques, such as dual-frequency receivers or suitable augmentation systems (Differential Global Positioning System -DGPS, Satellite Based Augmentation System -SBAS), predicted Global Ionospheric Maps (GIM) maps have been used in the past for real-time correction [2,3,4]
For the Global Positioning System (GPS), the Single Frequency Ionospheric Correction Algorithm is based on the Klobuchar model, which is a single-layer ionospheric model that employs eight broadcast coefficients from the navigation message to compute Slant Total Electron Content (STEC) based on a simple cosine function [5]
Summary
The performance of a GNSS system which provides three-dimensional position with global coverage is defined by the level of accuracy of the calculated position. Commercial single frequency stand-alone receivers are the cheapest and most widespread GNSS devices They have the capability to estimate and partially correct the error due to the ionosphere, through algorithms, which use parameters broadcasted in the navigation message [5,6]. These algorithms provide ionospheric delay estimation, from Slant Total Electron Content (STEC), defined as the electron concentration along the path between the receiver and the satellite, measured in Total Electron Content Units (1 TECU = 1016 el m−2). For the Global Positioning System (GPS), the Single Frequency Ionospheric Correction Algorithm is based on the Klobuchar model, which is a single-layer ionospheric model (treating the ionosphere as a condensed electron content layer located at 350 km) that employs eight broadcast coefficients from the navigation message to compute STEC based on a simple cosine function [5]
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