Research on field-aligned propagation of HF radiowaves using Alouette 2 topside sounder data and digital ray-tracing techniques
Jan Herman, Jayaram Ramasastry, Edward J. Walsh · NASA Technical Reports Server (NASA) · 1968
The first part of this technical note covers the study of guidance of HF radiowaves along field-aligned paths using the top side sounder data from the Alouette 2 satellite.More than 100,000 Alouette 2 ionograms have been used in this analysis and an un usually high percentage of occurrence of conjugate echoes has been observed in the data of some equatorial stations.The maximum per centage of occurrence of conjugate traces around local midnight when the satellite is near the apogee (3000 km) throws some light on the diffusion mechanism responsible for the formation of fieldaligned irregularities.The Singapore data (Geomagnetic longitude 1800 +30°) has shown higher occurrence of ducted echo-traces (>lo percent) than the data from all other stations.This is rather a large percentage.The longitudinal preference may be conducted with the larger magnetic field strengths in that longitudinal range.Two interesting types of ionograms containing conjugate echo traces are presented.They are called the "double hook" and the "triple hook" types.A self-consistent explanation based on the assumption of multiple reflections between conjugate points of the field line passing through the satellite is presented.The second part of the note covers the results of the digital ray-tracing study of the guidance of HF radiowaves along fieldaligned ionization irregularities in the magnetosphere of the Earth.Various computer results are shown to illustrate the mechanism of guidance of radiowaves.Time-delay and trapping characteristics of the two types of conjugate echoes that are frequently observed in the Alouette 2 topside sounder records are simulated using the ray-tracing methods.Some of the optimum conditions for guidance of electromagnetic waves along a magnetic field line are discussed.The results reported here on the HF ducting phenomenon is directed primarily towards determining whether such a mechanism may be utilized to study the magnetospheric phenomena and whether it can be useful as a reliable communication link.