Global ionospheric model development and utilisation for novel radio systems

Nugent, Luke ORCID: 0000-0002-8867-0900 (2024). Global ionospheric model development and utilisation for novel radio systems. University of Birmingham. Ph.D.

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Abstract

Global ionospheric models have a wide range of uses in addition to developing the understanding and characterisation of the ionosphere. Two examples of these uses are explored within this work, both of which use ionospheric models to predict ionospheric impacts to radio transmissions as they pass through the ionosphere. The first example is the impact of the ionosphere on High Frequency (HF) propagation, namely in the context of a multistatic over the horizon radar (OTHR) simulation. By ray tracing through output from an ionospheric model, the sensitivity of a simulated multistatic OTHR (MOTHR) has been compared to the sensitivity of a simulated, conventional monostatic OTHR configuration. The MOTHR requires a target signal to be detected by the monostatic receiver and at least one bistatic receiver simultaneously. This makes it possible for a target velocity to be determined from a single radar sweep, and makes it easier to distinguish the signal scattered by the target from the signal scattered by illuminated terrain or water waves. The region for which targets could be detected by the MOTHR was very similar to the coverage area for a monostatic OTHR configuration. The monostatic configuration could detect smaller targets than the MOTHR configuration; however, the loss of sensitivity was not severe for most locations, and small targets could still be detected with the MOTHR.

The second example is the impact of the ionosphere on Ultra High Frequency (UHF) propagation, focusing on the impact of ionospheric irregularities on Global Navigation Satellite System (GNSS) transmissions. Transmissions passing through regions with sudden changes in plasma density can result in rapid fluctuations of signal amplitude or phase, referred to as ionospheric scintillation. These sudden changes in plasma density take the form of plasma bubbles at low latitudes, which can considerably degrade GNSS performance in that region. A novel method to forecast the scintillation due to plasma bubbles at low latitudes has been developed. This method is shown to have forecasting skill as good as, or better than, an existing method when using output from the same physics based ionospheric model. Modelled electron densities are used to determine a proxy for vertical plasma drift (PVPD) speeds at the post sunset magnetic equator, which are used as an indicator of whether scintillation will occur. PVPD forecasting using a global ensemble data assimilation ionospheric model is shown to have a significant improvement in forecasting skill compared to PVPD forecasting with the physics based model for a single test case. A methodology to use ensembles of PVPD values to produce probabilistic scintillation forecasts is also discussed.

The accuracy of HF ray tracing and scintillation forecasting within this work are dependent on the quality of the ionospheric specification. Furthermore, excellent ionospheric specification would be crucial for, e.g., coordinate registration in an operational MOTHR. A technique to potentially improve the accuracy of an ensemble data assimilation model of the ionosphere by increasing variability between ensemble members is described. Additional variability between ensemble members can be generated by adding perturbations to lower boundary horizontal wind speeds. It is shown that lower boundary perturbations impact ionospheric conditions at higher altitudes, and can increase the range of modelled ionospheric conditions.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):