EVALUATION OF THE GNSS POSITIONING PERFORMANCE UNDER INFLUENCE OF THE IONOSPHERIC SCINTILLATION

Mayara Cobacho Ortega Caldeira,Carlos Rodrigo Tanajura Caldeira,Samara Sunny Dos Anjos Cereja,Claudinei Rodrigues De Aguiar,Daniele Barroca Marra Alves

doi:10.1590/s1982-21702020000300014

Abstract

The ionosphere may not only degrade the accuracy of the GNSS positioning but also reduce its availability because there is a high dependence between signal losses and ionospheric irregularities. Irregularities in the Earth’s ionosphere may produce rapid fluctuations in phase and amplitude. These rapid fluctuations are called ionospheric scintillation. Thus, loss of signal can occur due to the effects of diffraction and refraction, which cause a weakening in the signal received by the GNSS receivers. In this way, this paper aims to evaluate the magnitude of ionospheric scintillation in Brazil and the performance of the positioning under its influence in the period of high solar activity in the current cycle (24), through the Spearman correlation analysis and the Wavelet periodogram. For that, three-year time series (2012 to 2014) of the S4 index and 3D MSE (Mean Squared Error) of three Brazilian stations with different ionospheric conditions were considered, PALM (near the Geomagnetic Equator) PRU2 (Equatorial region and Anomalies) and POAL (Mid-latitude region). Thus, it was possible to evaluate the correlation between the accuracy of the precise point positioning using only the C/A code of the GPS satellite and the S4 index. As a result, there was a correlation of 53% and 51%, using the Spearman method, for the PALM and PRU2 series, respectively. In addition, considering the analysis of space-frequency in relation to time by the Wavelet coherence method, a correlation of more than 70% is noted in the period of greatest 3D MSE concerning the spring and autumn equinox months.

Highlights

Nowadays, space technologies have been widely employed, among them one of the main and most modern ones is the GNSS (Global Navigation Satellite System)
The first being located in a region that suffers a great influence of the ionospheric scintillation, since it is located close to the geomagnetic latitude 22°S, region that suffers major ionospheric effects, such as Equatorial Plasma Bubbles (EPB) and Equatorial Ionization Anomaly (EIA)
When relating the positioning error to the ionospheric scintillation S4 index, it is noted that in the period of intense ionospheric irregularities, which goes from the spring equinox (September - November) to the autumn equinox (March and April), these values are reduced around 3 times, obtaining an Mean Squared Error (MSE) around the meter or sub-meter

Summary

Introduction

Space technologies have been widely employed, among them one of the main and most modern ones is the GNSS (Global Navigation Satellite System). The data transmitted by the GNSS systems are subject to error, either due to the satellites themselves that compose the constellations, as well as the signal propagation, receiver and the station. Most of these errors can be eliminated, reduced, or modeled. The ionosphere became the main source of systematic error in GNSS positioning for single frequency receivers, after the deactivation of the SA (Selective Availability) technique on May 2, 2000 (Monico, 2008; Matsuoka, 2007; Seeber, 2003)

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Conclusion