13:45 〜 15:15
[MIS24-P01] A consideration on the identification of electron density in the D-layer using electric field variation of the VLF/LF earth-ionosphere waveguide propagation
キーワード：VLF波、大地-電離圏導波管、有限差分時間領域法
Identification of Electron density in the D-layer still remains a challenging problem, and one of the powerful methods is to use the sub-ionospheric propagation in the Very-Low-Frequency/Low Frequency (VLF/LF) bands. Previously, our group proposed an identification method and presented its validation numerically. However, it requires a comparison of absolute field amplitude between observation points, which is impractical because the comparison is extremely difficult. In this study, we develop a more practical method which uses temporal variation of electric fields.
The electron density profile is represented by Wait's empirical formula with two parameters: the effective height and the sharpness factor. As a numerical validation, we generate observational data through numerical simulations (FDTD method) with an assumed daily variation of the Wait's parameter. Then, using the generated observation data, we identify the parameters corresponding to the least square solution to minimize the difference in the temporal variation of electric fields.
We evaluate the proposed method by considering propagation from the JJI transmitter (frequency 22.2kHz, Ebino, Miyazaki) to the Tokyo area. Seven observation points are set at intervals of 100km, ranging from 300 km to 900 km from the transmitter. The results indicate that successful identifications are obtained with an error of less than 600m in altitude for electron densities of 107 to 108. Especially at sunrise and sunset, the identification is possible with an error of less than 500m for all electron densities.
The electron density profile is represented by Wait's empirical formula with two parameters: the effective height and the sharpness factor. As a numerical validation, we generate observational data through numerical simulations (FDTD method) with an assumed daily variation of the Wait's parameter. Then, using the generated observation data, we identify the parameters corresponding to the least square solution to minimize the difference in the temporal variation of electric fields.
We evaluate the proposed method by considering propagation from the JJI transmitter (frequency 22.2kHz, Ebino, Miyazaki) to the Tokyo area. Seven observation points are set at intervals of 100km, ranging from 300 km to 900 km from the transmitter. The results indicate that successful identifications are obtained with an error of less than 600m in altitude for electron densities of 107 to 108. Especially at sunrise and sunset, the identification is possible with an error of less than 500m for all electron densities.