Explore the Echo Characteristics of HF Radar in Artificial Disturbance Ionosphere Using Ray-Tracing Technology

Artificial ionospheric hole created by the release of neutral gases (such as sulfur hexafluoride) has a significant impact on the propagation of radio waves. Based on the ray-tracing method, the propagation patterns of HF radio waves in the ionospheric hole and the characteristics of its echoes are discussed in this paper. The results show that the HF waves will be deflected and bended while passing through the ionospheric hole, thus changing its original path. The sounding frequency, elevation angle, position of transmitter and receiver, and the dynamic variation of the hole all affect the reception of echoes. Generally, when the frequency is low, the echoes received on the ground mainly come from rays with low-elevation angles, and the multi-hop rays are more likely to occur. While with a high frequency, the received echoes are mainly contributed by high-elevation rays. It is not conducive to the reception of the echoes if the transmitter and receiver is too far away from the hole. Single-peak, double-peak and multi-peak echo signals can be found in the group path-amplitude diagram, and the maximum group path difference can reflect the size of the ionospheric hole to some extent. Due to the dynamic evolution of the hole, the propagation of HF waves and received echoes also changes over time. The group path-time diagrams show that the come-back echoes mainly appear in the period of 20-100 s after release. The results of this paper have a guiding significance for the diagnosis and application of active experiments.