The product was developed in collaboration with the Universidad Autónoma de Sinaloa, Mexico (www.uas.edu.mx) as a part of the research stay of the student Angela Melgarejo Morales.
Total Electron Content (TEC) is the quantity of electrons in a column of unit cross section of 1 m2 along the path from the GNSS signal transmitter to receiver. It is an important parameter that characterizes the state of the Earth’s ionosphere. Absolute vertical TEC values are reconstructed using the data extracted from a combination of code and phase measurements by GNSS receivers. TEC unit is defined as TECU=1016el/m2.
Global Ionospheric Maps (GIM) technique developed by different research centers (please, see references below for more details) provides the opportunity for constructing the absolute vertical TEC global maps based on the experimental data from the receivers of the International GNSS Service (IGS) network (www.igs.org/network) with use of interpolation. Usually, in GIM technique the ionosphere is considered a spherical layer of zero-thickness at a fixed height. GIM TEC is a reliable means for estimating the changes in the ionosphere state. The spatial resolution is 5o longitude and 2.5o latitude worldwide.
GIM TEC are produced by several Analysis Centers of the International GNSS Service (IGS) and are available in the “IONosphere Map Exchange” (IONEX) format. These independently calculated maps are then ranked and combined according to corresponding weight to produce the IGS global TEC maps (combined product).
The GIM TEC in the IONEX-format is freely available by following the link https://cddis.nasa.gov/archive/gnss/products/ionex.
The following papers and references therein may be useful for understanding the GIM TEC issue.
 Schaer, S., G. Beutler and M. Rothacher (1998). Mapping and predicting the ionosphere, Proc. IGS AC Workshop, Darmstadt, Germany, February 9-11, 307-320.
 Hernandez-Pajares, M., J.M. Juan and J. Sanz (1997). High-resolution TEC monitoring method using permanent ground GPS receivers, Geophys. Res. Lett., 24, 1643-1646.
Sardon, E., A. Rius and N. Zarraoa (1994). Estimation of the receiver differential biases and the ionospheric total electron content from Global Positioning System observations, Radio Sci., 29, 577-586.
 Jakowski, N., E. Sardon, E. Engler, A. Jungstand and D. Klahn (1996). Relationships between GPS-signal propagation errors and EISCAT observations, Ann. Geophys., 14, pp.1429-1436
 Mannucci, A.J., B.D. Wilson, D.N. Yuan, C.H. Ho, U.J. Lindqwister and T.F. Runge (1998). A global mapping technique for GPS-derived ionospheric total electron content measurements, Radio Science, 33(3), 565-582.
 Hernandez-Pajares, M., Juan J.M., Orus R., Garcia-Rigo A., Feltens J., Komjathy A., Schaer S.C. and Krankowski A. (2009). The IGS VTEC maps: a reliable source of ionospheric information since 1998, J. Geod., 83, 263–275.
 Afraimovich, E.L. and N.P. Perevalova (2006). GPS monitoring of Earth upper atmosphere, Irkutsk, Russian Academy of Sciences, Siberian Branch, 460p., ISBN 5-98277-033-7.
 Peng Chen, Hang Liu, Yongchao Ma, Naiquan Zheng (2019), Accuracy and consistency of different global ionospheric maps released by IGS ionosphere associate analysis centers, Advances in Space Research, doi: 10.1016/j.asr.2019.09.042.
 Arikan, F., C. B. Erol, O. Arikan (2003), Regularized estimation of vertical total electron content from Global Positioning System data, J. Geophys. Res., 108(A12), 1469, doi: 10.1029/2002JA009605.
 Z. Li, N. Wang, M. Hernández-Pajares, Y. Yuan, A. Krankowski at al. (2020), IGS real-time service for global ionospheric total electron content modeling, Journal of Geodesy, doi: 10.1007/s00190-020-01360-0.
The IONEX READER program was developed for convenient extraction of TEC values from IONEX-files of different time-resolution for different observation points.
Download IONEX READER program
Please read the section “About” and “Help”. The description of the program is available in Russian, English, Spanish and French.
If you have any questions/comments about IONEX READER, please contact: Dr. Maria Sergeeva (email@example.com).
If any publication or presentation is claiming use of the IONEX READER software, the authors must include an acknowledgement statement as follows: We thank Dr. Melgarejo Morales (UAS) and Dr. Sergeeva (SCiESMEX) for the opportunity to use IONEX Reader program.