Characteristics of higher order ionospheric effects on GNSS observations: Monitoring using IGS network

The ionospheric refractive index equation along the GNSS ray path includes second and third order terms. These as well as geometric and slant Total Electron Content (TEC) difference ray bending effects are usually referred to as higher order ionospheric effects. Unlike first order effects, these can not be eliminated using a linear combination of dual frequency observations. Higher order effects (mainly second order term) can reach several centimeters especially at low elevation angle observations and during ionospheric storm conditions [1, 2]. It has been shown that higher order ionospheric effects can affect high precision positioning applications, especially satellite orbit and clock estimation from global GNSS network data [1, 3].