5:15 PM - 7:15 PM
[PEM12-P30] Estimation of propagation paths and attenuation of HF radio waves treated as ordinary and extraordinary waves
Keywords:Ionosphere, Radio Propagation, Ordinary Wave, Extraordinary Wave, Attenuation, HF Doppler
When HF radio waves propagate through the ionosphere, there are two propagation modes: the ordinary wave and the extraordinary wave. When these propagation modes are separately considered, it is necessary to include the effects of the Earth's magnetic field in the Appleton-Hartree equation. If the effects of Earth's magnetic field's influence are not considered, only the ordinary wave remains, and the refractive index can be expressed using a simplified formula. However, this approach does not allow for the treatment of extraordinary waves.
In reality, both modes exist. Therefore, when considering actual radio wave propagation, it is necessary to handle each mode separately. In this study, ray tracing was used to derive the propagation paths of both the ordinary and extraordinary waves and to estimate the attenuation along each propagation path. Additionally, a comparison was made with the observed signal intensity obtained through HF Doppler observations to verify whether the derived results reflect realistic propagation.
For this study, observational data of the signal intensity were used, with Chofu as the transmission point and Sugadaira as the reception point. The diurnal and seasonal variations in attenuation were primarily dependent on the electron density distribution in the ionosphere. Attenuation was greater during the daytime when electron density increased, and it tended to reach its maximum, particularly during the daytime in spring and autumn. These variation trends were similar for both the ordinary and extraordinary waves. Furthermore, when comparing the attenuation of ordinary and extraordinary waves, the attenuation of the extraordinary wave was larger than that of the ordinary wave. For example, in 2015, the maximum attenuation values were approximately 10 dB for the ordinary wave and about 30 dB for the extraordinary wave. Next, these results were compared with the signal intensity data in the ray paths between Chofu and Sugadaira obtained through HF Doppler observations. The actual reception intensity data also exhibited the same variation trends as the model, with greater attenuation occurring during the daytime and increasing attenuation from spring to autumn. Additionally, when examining the relationship between these trends and solar activity, it was observed that during periods of high solar activity, the variation trends were relatively similar to those of the ordinary wave. However, in the reception intensity calculated for the ordinary wave during daytime in spring, a difference of about 2 to 8 dB was observed compared to the actual observations. On the other hand, in 2009, when solar activity was low, the diurnal variation in reception intensity closely resembled the estimated reception intensity variation due to the extraordinary wave. This suggests that when solar activity is low, the electron density in the ionosphere decreases, and the propagation of the extraordinary wave dominates.
In reality, both modes exist. Therefore, when considering actual radio wave propagation, it is necessary to handle each mode separately. In this study, ray tracing was used to derive the propagation paths of both the ordinary and extraordinary waves and to estimate the attenuation along each propagation path. Additionally, a comparison was made with the observed signal intensity obtained through HF Doppler observations to verify whether the derived results reflect realistic propagation.
For this study, observational data of the signal intensity were used, with Chofu as the transmission point and Sugadaira as the reception point. The diurnal and seasonal variations in attenuation were primarily dependent on the electron density distribution in the ionosphere. Attenuation was greater during the daytime when electron density increased, and it tended to reach its maximum, particularly during the daytime in spring and autumn. These variation trends were similar for both the ordinary and extraordinary waves. Furthermore, when comparing the attenuation of ordinary and extraordinary waves, the attenuation of the extraordinary wave was larger than that of the ordinary wave. For example, in 2015, the maximum attenuation values were approximately 10 dB for the ordinary wave and about 30 dB for the extraordinary wave. Next, these results were compared with the signal intensity data in the ray paths between Chofu and Sugadaira obtained through HF Doppler observations. The actual reception intensity data also exhibited the same variation trends as the model, with greater attenuation occurring during the daytime and increasing attenuation from spring to autumn. Additionally, when examining the relationship between these trends and solar activity, it was observed that during periods of high solar activity, the variation trends were relatively similar to those of the ordinary wave. However, in the reception intensity calculated for the ordinary wave during daytime in spring, a difference of about 2 to 8 dB was observed compared to the actual observations. On the other hand, in 2009, when solar activity was low, the diurnal variation in reception intensity closely resembled the estimated reception intensity variation due to the extraordinary wave. This suggests that when solar activity is low, the electron density in the ionosphere decreases, and the propagation of the extraordinary wave dominates.