This article relates to versions of PosApp (SimGEN / SimREPLAYplus / SimREPLAY) from v2.91 onwards. Note too that only SimGEN mode users have the ability to edit the scintillation feature.
PosApp software employs the Cornell scintillation model. This defines an "S4" index value which describes the intensity of the scintillation effect. In the real world scintillation intensity is directly related to the TEC ("Total Electron Count") - the higher the TEC the more severe the scintillation effect. However, the Cornell model does not rely on knowledge of the TEC to calculate the S4 index. Rather it is based on the approach of employing a statistical model which most closely matches empirical data; gathered from various sources by the Cornell team.
In PosApp the scintillation effect is applied as an offset to the other atmospheric model conditions (Tropospheric and Ionospheric) specified in the scenario’s atmosphere file. This means that there is no relationship between the TEC value quoted or calculated in the ionospheric model portion of the atmosphere file and the S4 Index values used in the scintillation model portion of the atmosphere file.