Printer FriendlyEmail Article Link

Is there a way of estimating the ionospheric delay using the scintillation model S4 index in PosApp?


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.

In PosApp the ionospheric delay (as seen in the software data output, and applied to the RF signal) is defined by the ionospheric model being applied in the scenario’s atmosphere file. In addition, and independently to this, we apply the effect of the scintillation model which creates additional offsets to the signal carrier phase and signal level. For SimGEN mode users Quick-look data offers a convenient way to observe the effect of scintillation on the RF signal by selecting data output for:

  • Signal level
  • Doppler and/or carrier pseudorange rate
  • Carrier pseudorange

Figure 1 demonstrates, using Quick-look logging to extract PosApp's data for manipulation with Excel (or other suitable data analysis tool), the comparison of one satellites signal level and Doppler shift with and without the presense of scintillation. For the benefit of the plots an S4 value of 0.8 has been used. You can see that scintillation primarily disrupts signal power.

Applying scintillation as an additional effect to the ionospheric model rather than instead of the ionospheric model is due to the fact that the Cornell scintillation model is a statistical approach to modelling the effects caused by scintillation on the RF signal and not a new way of modelling the ionosphere directly.

Therefore, simply an understanding of the Cornell model and how different values of the S4 index affect the signal carrier phase (this also being dependent on time of day, satellite and vehicle geometry, i.e. ionospheric pierce-point), will not give a final value for ionospheric delay since you would still also need to account for the effect of the active ionospheric model in the scenario.

Product : Positioning,SimREPLAYplus,SimREPLAY,SimGEN,PosApp,Atmosphere