Comparison between TEC values derived from antarctic GPS measurements and atmospheric soundings

Ionospheric refraction introduces a delaying effect on GPS observables (code and carrier phase measurements) and therefore on the precise relative position derived. This cannot be completely solved by GPS dual frequency techniques that only take into account the geometric effect of the ionosphere (first order approximation; Ciraolo, 1994) considered as an undisturbed region associated with a constant vertical gradient of Total Electron Content TEC (Menge, 1996). Non-geometric effects also play a fundamental role in signal-ionosphere interactions mainly in equatorial and auroral regions (such as Antarctica) where the severe ionospheric conditions influence the GPS signals (scintillation phenomena). In an attempt to understand and model this effect, we computed the TEC values from selected 1993 GPS Antarctic dataset, using different GPS-based methods. Finally we compared the GPS-derived TEC values with those computed with the ionospheric model based on atmospheric soundings, performed simultaneously to the GPS measurements and in the same region (Terra Nova Bay, Antarctica) by a researcher from the Istituto Nazionale di Geofisica (Rome). The TEC values from GPS observables and atmospheric soundings showed good agreement, taking into account the extreme variability of the phenomenon investigated and the strong dependence on satellite orbital parameters (elevation and azimuth).