10:45 〜 12:15
[PEM12-P25] Observation of a temporally modulated HF wave propagating through ionosphere
キーワード：時間的に変調された短波、電離圏中の伝搬、連続Doppler計測、Doppler周波数遷移、飛行時間、相互相関
Ionosphere perturbed by vibrating atmosphere is observed by continuous Doppler sounding (CDS) of reflective HF waves. An HF wave of a single frequency is commonly used to observe Doppler frequency shift (DFS). It, however, does not serve for time of flight (ToF) observation in principle. Actually, ionosonde estimating reflection height of a sounding wave is incorporated with CDS for three-dimensional analysis of gravity wave propagation in ionosphere [1]. Temporally modulated HF waves are reported to serve for observation of both DFS and ToF [2,3]. A new Chung-Li ionosonde in Taiwan [4] is expected to provide us with better observation resolutions in time and frequency domains, since it transmits pulses of wide bandwidth and long coherent time.
The HF wave transmitted starting at 8:00 on November 22, 2022 (UT) was sampled in Amagasaki, Japan. Summed absolute values of cross-correlations between received samples and model replicas of frequency range from 10 through 15 MHz are plotted as a heat map against the replica frequency (horizontal axis) and the excess time of flight, defined as time of flight minus the time required for a photon to travel straight distance from the transmitter to the receiver in vacuum (vertical axis). Absolute values of cross-correlations with a replica of the same frequency are summed to increase the signal to noise ratio. It is interpreted that HF waves less than 11 MHz propagating in a multi-reflection path due to ionosphere were less attenuated than that in a single-reflection path.
A summed absolute value of cross-correlations between received samples and model replica of 13.5 MHz (vertical axis) is shown in Fig. 2 against the excess time of flight (horizontal axis). It is observed that the support of the summed absolute value of cross-correlations is consistent to a chip length of 25.5 microseconds used for temporal modulation of the replica, as annotated with red arrows. It is straightforward to derive that the first null frequency of the cross-correlation is about 2,451 Hz apart from the peak of the true frequency of received samples, as far as transmitted waves are modulated with an identical amplitude. This figure, which is frequently provided as frequency resolution, shows less than one-fifth of that for the HF wave we previously reported [2]. It is expected that samples received in future will serve for analysis of ionosphere with fine observation of DFS and ToF.
References:
[1] J. Chum and K. Podolská, “3D Analysis of GW Propagation in the Ionosphere,” Geophys. Res. Lett., vol. 45, 2018.
[2] T. Iwamoto, M. Konishi, N. Ikeda, and S. Kameoka, “Observation of Doppler frequency shift and time of flight of a temporally modulated HF wave propagating through ionosphere,” the Japan Geoscience Union Meeting 2022, Chiba, Japan, May 2022.
[3] T. Iwamoto and M. Konishi, “Observation of Doppler frequency shift and time of flight of a Morse code propagating through ionosphere,” IEICE Technical Report, vol. SANE2022-08, 2022.
[4] K.-J. Ke, C.-L. su, R.-M. Kuong, H.-C. Chen, H.-S. Lin, P.-H. Chiu, C.-Y. Ko, and Y.-H. Chu, “New Chung-Li Ionosonde in Taiwan: System Description and Preliminary Results,” Remote Sensing, vol. 14, 2022.
Figure captions:
Fig. 1: A heat map of summed absolute values of cross-correlations between the HF wave transmitted starting at 8:00 on November 22, 2022 (UT) and model replicas of frequency range from 10 through 15 MHz plotted against the replica frequency (horizontal axis) and the excess time of flight, defined as time of flight minus the time required for a photon to travel straight distance from the transmitter to the receiver in vacuum (vertical axis).
Fig. 2: A summed absolute value of cross-correlations between the HF wave transmitted starting at 8:00 on November 22, 2022 (UT) and a model replica of frequency 13.5 MHz (vertical axis) against the excess time of flight (horizontal axis).
The HF wave transmitted starting at 8:00 on November 22, 2022 (UT) was sampled in Amagasaki, Japan. Summed absolute values of cross-correlations between received samples and model replicas of frequency range from 10 through 15 MHz are plotted as a heat map against the replica frequency (horizontal axis) and the excess time of flight, defined as time of flight minus the time required for a photon to travel straight distance from the transmitter to the receiver in vacuum (vertical axis). Absolute values of cross-correlations with a replica of the same frequency are summed to increase the signal to noise ratio. It is interpreted that HF waves less than 11 MHz propagating in a multi-reflection path due to ionosphere were less attenuated than that in a single-reflection path.
A summed absolute value of cross-correlations between received samples and model replica of 13.5 MHz (vertical axis) is shown in Fig. 2 against the excess time of flight (horizontal axis). It is observed that the support of the summed absolute value of cross-correlations is consistent to a chip length of 25.5 microseconds used for temporal modulation of the replica, as annotated with red arrows. It is straightforward to derive that the first null frequency of the cross-correlation is about 2,451 Hz apart from the peak of the true frequency of received samples, as far as transmitted waves are modulated with an identical amplitude. This figure, which is frequently provided as frequency resolution, shows less than one-fifth of that for the HF wave we previously reported [2]. It is expected that samples received in future will serve for analysis of ionosphere with fine observation of DFS and ToF.
References:
[1] J. Chum and K. Podolská, “3D Analysis of GW Propagation in the Ionosphere,” Geophys. Res. Lett., vol. 45, 2018.
[2] T. Iwamoto, M. Konishi, N. Ikeda, and S. Kameoka, “Observation of Doppler frequency shift and time of flight of a temporally modulated HF wave propagating through ionosphere,” the Japan Geoscience Union Meeting 2022, Chiba, Japan, May 2022.
[3] T. Iwamoto and M. Konishi, “Observation of Doppler frequency shift and time of flight of a Morse code propagating through ionosphere,” IEICE Technical Report, vol. SANE2022-08, 2022.
[4] K.-J. Ke, C.-L. su, R.-M. Kuong, H.-C. Chen, H.-S. Lin, P.-H. Chiu, C.-Y. Ko, and Y.-H. Chu, “New Chung-Li Ionosonde in Taiwan: System Description and Preliminary Results,” Remote Sensing, vol. 14, 2022.
Figure captions:
Fig. 1: A heat map of summed absolute values of cross-correlations between the HF wave transmitted starting at 8:00 on November 22, 2022 (UT) and model replicas of frequency range from 10 through 15 MHz plotted against the replica frequency (horizontal axis) and the excess time of flight, defined as time of flight minus the time required for a photon to travel straight distance from the transmitter to the receiver in vacuum (vertical axis).
Fig. 2: A summed absolute value of cross-correlations between the HF wave transmitted starting at 8:00 on November 22, 2022 (UT) and a model replica of frequency 13.5 MHz (vertical axis) against the excess time of flight (horizontal axis).