Ionospheric Corrections for Space Domain Awareness Using HF Line-of-Sight Radar

As the near-Earth space domain becomes increasingly congested, the field of space domain awareness (SDA) has risen in importance and motivated the use of non-traditional sensors. One such class of sensor is high frequency (HF) radar operating in line-of-sight (LOS) mode, as their large surveillance field-of-view enables simultaneous tracking of several objects. HF signals are, however, subject to ray bending and group retardation when propagating through the ionosphere. This paper demonstrates the development and implementation of a method for calculating the ionospheric correction for HF LOS satellite observations, using three-dimensional numerical ray tracing through a climatological model ionosphere. Defence Science and Technology Group’s experimental HF LOS radar was deployed during a SpaceFest trial in late 2020, and recorded observations of resident space objects (RSOs). The ionospheric correction is applied to these observations and compared to propagations obtained from the reported two line elements (TLEs) of the RSOs to assess the correction performance. The results demonstrate that, even during weak ionospheric conditions, ray tracing through a climatological model ionosphere produces a significant improvement in the residuals between the range measurements and TLEs. The application of ionospheric corrections was found to be crucial for the reliable use of HF radar for SDA during any stage of the solar cycle.