Ionospheric Propagation Loss Model

The computation for propagation loss through the ionospheric layer is based on the ITU-R P.531-13 recommendation. The total electron content (TEC) along the propagation path causes polarization rotation due to Faraday rotation. STK estimates TEC by using the International Reference Ionosphere (IRI) model and integrating electron density over the actual path through the ionospheric layer.

STK uses section 3.2 of the ITU-R P.531-13 recommendation to compute the Faraday rotation and the cross-polarization discrimination for aligned antennas to estimate the potential loss. You should use the model based on the system polarization type. For example, circular polarization is expected to experience little impact, while linear polarization systems may be very sensitive to small rotations. Also, smaller wavelengths may see more phase changes (and higher loss) from minor position changes. STK leaves it up to you to be aware of the sensitivity of the results to the environmental factors (TEC) and the platform dynamics and to apply good judgment in using the model.

The reference data used by the IRI model is an integral part of the model, and the IRI conference regularly issues updates to the data. STK’s computations use the Space Weather access point (AP) data file. Using the 2016 version (updated for September 2019 changes) of the IRI model, STK computes the TEC and ionsospheric noise temperature.

AGI routinely updates APF107.data and ig_rz.dat. However, for a given release, the data will eventually become outdated. In the event the STK Message Viewer states that data is not available for the scenario date, you should consider updating the APF107.data file in the DynamicEarthData subfolder. You can obtain both of these data files from the International Reference Ionosphere website or from the AGI data server. On the AGI data server, download DataUpdate.zip and open the DynamicEarthData folder to access these files. You can also use STK's Data Update Utility, under the Utility menu, to retrieve these data files. Please contact support@agi.com if you need assistance.

Alternate AP data

For the Iono Fading tab of the RF Environment properties, the following fields provide the option to use alternate AP data.

Parameter	Description
UseAlternateAPFile	Select this check box to override the built-in AP dataset.
AlternateAPDataFile	Click the ellipsis to find and select a user-supplied file. This file will override the ap.dat file provided by the IRI model.