[P-EM09] Space Weather and Space Climate

[PEM09-27] Validation of HF Radio attenuation calculation using HF Doppler observation

Shun Sato¹, *Hiroyuki Nakata², Kornyanat Hozumi³, Susumu Saito⁴, Keisuke Hosokawa⁵, Hiroyo Ohya² (1.Graduate School of Science and Engineering, Chiba University, 2.Graduate School of Engineering, Chiba University, 3.National Institute of Information and Communications Technology, 4.Electronic Navigation Research Institute, National Institute of Maritime, Port and Aviation Technology, 5.The University of Electro-Communications )

Keywords:HF radio wave, absorption, ray tracing, HF Doppler

Since the ionospheric conditions for radio wave propagation change diurnally and seasonally, the accurate estimation of the current state of radio wave propagation would be very useful. We have already developed the web service providing the propagation paths of HF radio waves as part of the HF-START (HF Simulator Targeting for All users’ Regional Telecommunications) project. On the other hand, actual radio waves are attenuated by various causes, and the signal intensity varies depending on the ionospheric conditions and propagation path. Therefore, in addition to the propagation paths, it is quite helpful to estimate the signal intensity of radio waves.
To provide information on the signal intensity, we have developed a calculator to determine the attenuation of HF radio waves in the ionosphere. The main factors for the attenuation of HF radio waves are (1)particle collisions in the ionosphere, (2)ground reflection, and (3) free space loss. In this study, the attenuation due to particle collisions in the ionosphere was estimated simultaneously with the raytracing calculation of the propagation paths. The absorption coefficient of the radio wave was adopted from that defined by Davies (1990).
We compared the temporal variation of the signal intensity of the o-mode radio wave with those observed by HF Doppler Sounding. In this comparison, we set the transmitting and receiving points as Chofu Campus (at the University of Electro-Communications 35.657N, 139.543E) and Sugadaira (36.423N, 138.318E), respectively. The frequency of the radio waves was 5.006 MHz. As a result, the dependences of daily and seasonal variations on the signal intensity were very similar between the simulation and the observations: the signal intensity decreased during the daytime and summer when the electron density was large. This result also implies that the propagation mode of HF Doppler Sounding between Chofu and Sugadaira is o-mode. These results suggest that the estimation of the absorption in this study helps estimate the realistic signal intensity for propagation between any two points on the ground.