[P-EM13] Coupling Processes in the Atmosphere-Ionosphere System

[PEM13-P08] Calculation of attenuation of HF radio waves in the simulator for HF-START project

*Shun Sato¹, Hiroyuki Nakata¹, Kornyanat Hozumi², Susumu Saito³, Hiroyo Ohya¹ (1.Chiba University, 2.National Institute of information and Communications Technology, 3.Electronic Navigation Research Institute)

HF-STRAT (HF Simulator Targeting for All user's Regional Telecommunications) is a web-based information service to provide nowcast information on HF radio wave propagation. In HF-START, HF radio propagation is determined by ray tracing calculation with electron density profiles in the ionosphere. Information such as the propagation path and propagation time between any two points can be obtained. Since the current HF-START does not have a function to evaluate the signal intensity, we are in the process of implementing a function to calculate the attenuation of the radio wave. The factors of the attenuation to be considered are (1) collisions of the plasma and neutral particles in the ionospherer, (2) ground reflection, (3) aurora, (4) free space path loss, and (5) other factors. To calculate the attenuation factor (1), we use the electron-ion collision frequency, electron-neutral particle collision frequency and electron density, and integrate the attenuation along the path to obtain the whole amount of attenuation. The attenuations due to (2), (4), and (5) are estimated by referring to the formula described in ITU-R P533. Regarding the ITU-R P533, the attenuation by (2) is assumed to be 2 dB per hop, and the attenuation by (5) along the Tx-Rx path is assumed to be 8.72 dB. The attenuation due to the aurora is defined statistically in ITU-R P533, but it may be proper that the auroral effects can be taken into account by evaluating values from optical observations and/or AE indices. Therefore, the effects of the aurora are not taken into account for this implementation at the moment. In addition, this calculation only considers the attenuation along the propagation path between the two points and does not take into account the focusing/defocusing due to ionospheric inhomogeneity. In this presentation, we will show the results of the calculation.