Radio wave propagation aspects of the CUTLASS radar

Abstract

The performance of the HF radars such as the collaborative UK twin located auroral sounding system, depends critically on the propagation characteristics of HF radio waves in the ionosphere. The transmission paths through the ionosphere have been determined by ray tracing techniques applied to suitable models of the electron density height distribution. By launching waves at a range of elevation angles, it has been possible to calculate the skip distance and ground illumination flux of each radar for the operating frequency (10 MHz). The calculated and measured positions of the ground backscatter are found to be in excellent agreement, indicating that this modelling approach can predict the performance of the radar for any conditions for which a representative electron density height profile can be established. When waves of very high power are propagated through the ionosphere, artificial irregularities are produced which can be detected by the HF radars in a similar manner to those occurring naturally. The advantage of the heater-induced irregularities is that they can be generated at will and can form a ‘window’ through which many geophysical phenomena (e.g. ULF waves) can be investigated. Examples of the applications of this technique are presented, and it is evident that it has great potential for a range of geophysical investigations.