5:15 PM - 6:45 PM
[PEM12-P28] Introduction of the distance measurement function and observation examples of the new HF Doppler observation system
Keywords:HF Doppler, observation system, FM-CW, radar altimeter
The HF Doppler (HFD) ionospheric observation system of the University of Electro-Communications (UEC) has been in operation since 2001 (Tomizawa et al., 2003). We continuously observe various ionospheric phenomena in the mid-latitude E and F regions over Japan. It features multi-point bistatic observations and provides multi-frequency HFD data at multiple locations (http://gwave.cei.uec.ac.jp/~hfd). The Doppler shift data represent the temporal variation of the phase path length of the reflected wave, which often corresponds to the vertical motion of the ionosphere, and has been used to study propagating ionospheric disturbances, sporadic E phenomena, and ionospheric variations associated with energy inputs from the magnetosphere or lower atmosphere.
The transmission of radio waves from UEC has two frequencies: 5.006 MHz and 8.006 MHz at 200 W power, and is operative 24 hours a day. At JpGU 2022, we first introduced the concept of adding ranging functions based on the FM-CW method to the existing system, and since then have reported the development status of the new system. In this paper, results from the actual test measurement with the bistatic FMCW radar will be reported.
The new HFD observing system transmits FMCW signals with the center frequency of 8006 kHz and 5006 kHz. These frequencies are also used for the Doppler frequency observations. Frequency-swept FMCW signals are superimposed on the CW signals in the range of ±75 kHz for ranging. As the observation system has multiple remote receiving points for a single transmit point, GPSDO was used for both the transmitting and receiving sites to synchronize the time of frequency sweeping. On the receiving side, the received signal and a replica signal of FMCW are combined by a mixer and captured by a software receiver.
The experiment was conducted by operating a FM-CW receiver at a distance of approximately 20 km away from the transmitter and measuring the actual spatial waves (i.e., direct wave and ionospheric reflection). Distinction of the FM-CW signal from UEC from external noise can be determined by the timing of the switching to the Morse signal every a few minutes. To assess the accuracy of the reflection altitude measurements, the FM-CW data were cross-evaluated with simultaneous observations of the Kokubunji Ionosonde. The altitudes derived from the FM-CW observation were found to be well consistent with those from the Ionosonde observation. It was also found to have high temporal and frequency resolution. In addition to these findings, the propagation distance of surface wave agreed with the actual distances from the transmitter with an accuracy of ~1 km. Finally, in combination with the Doppler observation data from nearby receiving points, we were also able to distinguish reflections from E and F regions of the ionosphere. In the presentation, we present the preliminary observation data from these test observations.
The transmission of radio waves from UEC has two frequencies: 5.006 MHz and 8.006 MHz at 200 W power, and is operative 24 hours a day. At JpGU 2022, we first introduced the concept of adding ranging functions based on the FM-CW method to the existing system, and since then have reported the development status of the new system. In this paper, results from the actual test measurement with the bistatic FMCW radar will be reported.
The new HFD observing system transmits FMCW signals with the center frequency of 8006 kHz and 5006 kHz. These frequencies are also used for the Doppler frequency observations. Frequency-swept FMCW signals are superimposed on the CW signals in the range of ±75 kHz for ranging. As the observation system has multiple remote receiving points for a single transmit point, GPSDO was used for both the transmitting and receiving sites to synchronize the time of frequency sweeping. On the receiving side, the received signal and a replica signal of FMCW are combined by a mixer and captured by a software receiver.
The experiment was conducted by operating a FM-CW receiver at a distance of approximately 20 km away from the transmitter and measuring the actual spatial waves (i.e., direct wave and ionospheric reflection). Distinction of the FM-CW signal from UEC from external noise can be determined by the timing of the switching to the Morse signal every a few minutes. To assess the accuracy of the reflection altitude measurements, the FM-CW data were cross-evaluated with simultaneous observations of the Kokubunji Ionosonde. The altitudes derived from the FM-CW observation were found to be well consistent with those from the Ionosonde observation. It was also found to have high temporal and frequency resolution. In addition to these findings, the propagation distance of surface wave agreed with the actual distances from the transmitter with an accuracy of ~1 km. Finally, in combination with the Doppler observation data from nearby receiving points, we were also able to distinguish reflections from E and F regions of the ionosphere. In the presentation, we present the preliminary observation data from these test observations.