Impact of Ionospheric Doppler Perturbations on Space Domain Awareness Observations

As the Low Earth Orbit (LEO) space environment becomes increasingly congested, the need to identify and track space objects has grown. This is currently achieved through a network of ground-based and satellite-mounted sensors. However, these sensors are expensive to produce and maintain which has led to an effort in finding alternative sensors to track satellites. One such alternative is radar operating in the high frequency (HF) and very high frequency (VHF) bands which have been shown to be able to detect space objects. We report on 393 days of satellite observations made by a VHF and HF radar and find evidence of Doppler perturbations across multiple observations in the spectrograms. Two environmental sources of these perturbations were found, with the most numerous being ionospheric plasma instabilities in the 0-0.46 Hz frequency range. The second source was identified as ionospheric plasma waves propagating parallel to the Earth’s surface in a waveguide centred at an altitude of250 km. To the authors’ best knowledge, this is the first time that radar has been used to observe such waves and a statistical study indicated that, under certain conditions, radar may provide a more sensitive measure of the plasma waves than magnetometers normally used to detect these waves. The results indicate that the Doppler perturbations produced by ionospheric plasma instabilities and waves do not significantly impact the Doppler uncertainty of space domain awareness measurements at HF and VHF frequencies.