# GNSS TEC Calibration

TEC data are derived from carrier phase measurements for both GPS or GPS +GLONASS satellite systems.

The basic relation used to calibrate the TEC is as follows:

S Φ = sTEC + βias arc

where:

S Φ is the ionospheric delay from the raw carrier phase observations,

βias is the arc-offset, a constant to be determined for each arc of observations related to a given receiver and satellite pair. βias represents the contribution of receiver and satellites biases (δbR, δbs), and the contribution of any non-zero averaged errors over an arc of observations, e.g. the multipath (<δm>arc).

A two-dimensional thin shell model at 350 km is used to define the mapping function between the slant and vertical TEC. The vertical ionospheric variation is expressed as a function of the modip and the Local Time of the ionospheric pierce points (IPPs).

There are major differences between the signals characteristics of GPS and GLONASS, relevant to TEC estimation. They are the navigation data and the nominal values of the transmitting radio-frequencies. Nevertheless, the calibration technique could be applied to simultaneous GPS/GLONASS measurements since the satellite and receiver biases are not explicitly separated.

Reference:Ciraolo, L., et al. "Calibration errors on experimental slant total electron content (TEC) determined with GPS." Journal of Geodesy 81.2 (2007): 111-120.

Calibration Fortran code implemented byKaty Alazo-Cuartas