Abstract
This manuscript explores the divergence of the Vertical Total Electron Content (VTEC) estimated from Global Navigation Satellite System (GNSS) measurements using global, regional, and International Reference Ionosphere (IRI) models over low to high latitude regions during various magnetic activity. The VTEC is estimated using a territorial network consisting of 7 GNSS stations in Egypt and 10 GNSS stations from the International GNSS Service (IGS) Global network. The impact of magnetic activity on VTEC is investigated. Due to the deficiency of IGS receivers in north Africa and the shortage of GNSS measurements, an extra high interpolation is done to cover the deficit of data over North Africa. A MATLAB code was created to produce VTEC maps for Egypt utilizing a territorial network contrasted with global maps of VTEC, which are delivered by the Center for Orbit Determination in Europe (CODE). Thus we can have genuine VTEC maps estimated from actual GNSS measurements over any region of North Africa. A Spherical Harmonics Expansion (SHE) equation was modelled using MATLAB and called Local VTEC Model (LVTECM) to estimate VTEC values using observations of dual-frequency GNSS receivers. The VTEC calculated from GNSS measurement using LVTECM is compared with CODE VTEC results and IRI-2016 VTEC model results. The analysis of outcomes demonstrates a good convergence between VTEC from CODE and estimated from LVTECM. A strong correlation between LVTECM and CODE reaches about 96 % and 92 % in high and low magnetic activity, respectively. The most extreme contrasts are found to be 2.5 TECu and 1.3 TECu at high and low magnetic activity, respectively. The maximum discrepancies between LVTECM and IRI-2016 are 9.7 TECu and 2.3 TECu at a high and low magnetic activity. Variation in VTEC due to magnetic activity ranges from 1–5 TECu in moderate magnetic activity. The estimated VTEC from the regional network shows a 95 % correlation between the estimated VTEC from LVTECM and CODE with a maximum difference of 5.9 TECu.
Acknowledgements
The author thanks nasa.gov and the Crustal Dynamics Data Information System (CDDIS) data center for providing RINEX files, navigation files by the following FTP server: ftp://cddis.gsfc.nasa.gov/pub/gps/data/daily/
P1–C1 code biases and precise ephemerides files of the study obtained from NASA (www.gnsscalendar.com)
Sunspot number and Kp indices ftp://ftp.swpc.noaa.gov
The VTEC data of the IRI-2016 via: https://ccmc.gsfc.nasa.gov/modelweb/models/iri2016_vitmo.php
Also, the author appreciates and acknowledged the use of MATrix LABoratory software (MATLAB).
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© 2022 Walter de Gruyter GmbH, Berlin/Boston
Articles in the same Issue
- Frontmatter
- Research Articles
- Evaluation of QZSS orbit and clock products for real-time positioning applications
- On the consideration of combined measurement uncertainties in relation to GUM concepts in adjustment computations
- A simple iterative algorithm based on weighted least-squares for errors-in-variables models: Examples of coordinate transformations
- Comparison of kriging and least-squares collocation – Revisited
- Validation of regional and global ionosphere maps from GNSS measurements versus IRI2016 during different magnetic activity
- Inverse geodetic problem for long distance based on improved Vincenty’s formula
- Regularizing ill-posed problem of single-epoch precise GNSS positioning using an iterative procedure
- Integration of GNSS observations with volunteered geographic information for improved navigation performance
- Studies on deformation analysis of TLS point clouds using B-splines – A control point based approach (Part I)
- Stability analysis of the Iraqi GNSS stations
- R-ratio test threshold selection in GNSS integer ambiguity resolution
Articles in the same Issue
- Frontmatter
- Research Articles
- Evaluation of QZSS orbit and clock products for real-time positioning applications
- On the consideration of combined measurement uncertainties in relation to GUM concepts in adjustment computations
- A simple iterative algorithm based on weighted least-squares for errors-in-variables models: Examples of coordinate transformations
- Comparison of kriging and least-squares collocation – Revisited
- Validation of regional and global ionosphere maps from GNSS measurements versus IRI2016 during different magnetic activity
- Inverse geodetic problem for long distance based on improved Vincenty’s formula
- Regularizing ill-posed problem of single-epoch precise GNSS positioning using an iterative procedure
- Integration of GNSS observations with volunteered geographic information for improved navigation performance
- Studies on deformation analysis of TLS point clouds using B-splines – A control point based approach (Part I)
- Stability analysis of the Iraqi GNSS stations
- R-ratio test threshold selection in GNSS integer ambiguity resolution