Dear Belay,

Are you referring to readily available TEC values?

For this you please visit IGS (International GNSS service) where they have given certain direction on how to go about it. If it is still difficult, kindly contact me, I might be able to redirect you to more helpful resources.

Or that you have a dual fre. GPS receiver and that you want to derive TEC from the delays?

This requires lots of understanding of the working of the receiver, bias and errors. Once we are sure that we know of all the error sources, there are some software, like bernese (I do  not know much about this) which calculates TEC.

Dear Belay,

I agree to Dr. K N Pathak , your question is not clear that you want readily available TEC values or you want to calculate those values from GPS data. So please specify what GPS data source you are using?

Best Regards

Although your question is not absolutely clear, you probably mean the way to acquire TEC data. One possible and easy way is to use the GIM (Global Ionosphere Maps) products by the IGS service. These products are published in IONEX format and contain the global scale Total Electron Content of the atmosphere in gridded maps.

Check here: ftp://cddis.gsfc.nasa.gov/pub/gps/products/ionex/ 

Since you want to perform electron and TEC fluctuation studies on the ionosphere, I strongly recommend you to check the ESA SSA Space Weather Portal, which gives access to a range of space weather products and applications such as:

The Ionospheric Scintillation Monitoring (ISM) service offering global and regional nowcast and forecast of the ionospheric scintillation indices S4 and SigmaPhi;

The Regional Auroral Forecast (RAF) service providing auroral forecast with several hours lead time. It delivers information on the occurrence of bright auroral displays in Fennoscandia and includes near-real-time images taken from Finnish auroral stations; The SWE Data Browsing and Analysis application offering access to a wide range of Space Weather related data sources relevant to the different service domains and including an analysis and visualisation tool.

It is accessible at http://swe.ssa.esa.int/ 

You can Calculate TEC Using Pseudo-Ranges, Calculate TEC Using Carrier Phase, Calculate TEC Combining Group and Phase Delay of GPS.

for instance the software available on line:

http://seemala.blogspot.com.br/2014/01/rinex-gps-tec-program-version-29.html

I think the next three research articles can describe in details How

How to calculate the TEC from GNSS data?

1- A global mapping technique for GPS-derived ionospheric total electron content measurements

By: A. J. Mannucci, B. D. Wilson, D. N. Yuan, C. H. Ho, U. J. Lindqwister, and T. F. Runge

2- Calibration errors on experimental slant total electron content (TEC) determined with GPS

By: L. Ciraolo ·, F. Azpilicueta ·, C. Brunini ·, A. Meza ·, S. M. Radicella

3- THE METHOD TO CALCULATE TEC USING GPS AND ITS APPLICATION TO THE STUDY OF IONOSPHERIC DISTURBANCES

By: ZHANG Dong-He and XIAO Zuo

Geometry-free combination: it cancels the geometric part of the measurement, leaving all the frequency-dependent effects (i.e., ionospheric refraction, instrumental delays, wind-up) besides multipath and measurement noise. It can be used to estimate the ionospheric electron content.

you can check ESA website:

https://gssc.esa.int/navipedia/index.php/Combination_of_GNSS_Measurements

Data sets on various time cadences are shared here:

https://cdaweb.gsfc.nasa.gov/pub/data/gps/

I posted a movie for one day here:

https://www.youtube.com/watch?v=hnbsp_T4_7U&feature=youtu.be

And scripts to read and display the data using matlab here:

https://www.mathworks.com/matlabcentral/fileexchange/73858-space-weather-global-tec-displayed-with-geoshow-mapshow

How to derive TEC and scintillation from a dual frequency GPS receiver's signal. Any help in this regard will be highly appreciated.