A comparison of techniques to determine the geolocation of plasma irregularities

The presence of plasma irregularities in the ionosphere can result in impacts to trans-ionospheric communications due to ionospheric scintillation (rapid fluctuations of the amplitude and/or phase of the received signal). Efforts to predict when scintillation could affect communications have included using ionospheric observations from ground-based stations in near-real time to provide nowcasting of plasma irregularities which may cause scintillation. These observations can then be propagated forwards in time using observations or predictions of irregularity drift velocities. However, the nowcasting ability of this approach is limited by the lack of ionospheric observations over some regions, e.g. the oceans.

Using radio occultation techniques, in which signals from GNSS satellites are detected by receivers on low earth orbit (LEO) satellites, ionospheric scintillation observations can be obtained over regions lacking ground-based receivers. However, determining the geolocation of the plasma irregularity (or irregularities) along the satellite-satellite ray path presents a further challenge. Existing techniques to geolocate the structures use the power spectral density (PSD) of the received signal amplitude to determine the Fresnel frequency which, along with the magnetic field orientation at the irregularity location and the satellite positions and velocities, can be used to determine the distance between the irregularity and the LEO satellite.

In this work methods to determine the Fresnel frequency from the amplitude PSD are compared. The primary focus is on nowcasting skill and computational cost, with the aim of establishing which techniques are suitable for nowcasting ionospheric scintillation in an operational setting.