Total Electron Content

The IONEX files that contain vTEC values are downloaded from online ftp-servers like:

ftp://ftp.unibe.ch/aiub/CODE/ or ftp://gnss.oma.be/gnss/products/IONEX/

The users can provide its own server url, but keep in mind that the directory format in which the data is saved (e.g. year/doy/) is hardcoded. If another server needs to be added that has a different format than the default CODE-server, please contact the developer.

The IONEX data typically is produced every 1 or 2 hrs with a spatial resolution of 2.5 to 5 degrees. In order to interpolate to location of the piercepoint, a inverse distance weighted average of the 4 nearest cells is used. The method suggested in Schaer et al (1997) to take into account the rotation of the Earth before averaging is also implemented. However it was found that this method didnot give stable results for the higher time resolution maps of ROB. Usage of this method can be controlled with the parameter apply_earth_rotation.

references:

Schaer, S., W. Gurtner, and J. Feltens (1997): 'IONEX: The IONosphere Map EXchange Format Version 1', February 25, 1998, in Proceedings of the 1998 IGS Analysis Centers Workshop, ESOC, Darmstadt, Germany, February 9-11, 1998.