Presentation Information
[AAS15-P11]On the Setting of Reflected Wave Arrival Time in Water Vapor Variability Observation Using Digital Terrestrial Broadcasting Waves
*Hayato Kon1, Ryoko Oda1, Hiroshi Hayado2, Seiji Kawamura2, Yoshiyuki Kawatani2 (1.Chiba Institute of Technology, 2.National Institute of Information and Communications Technology)
Keywords:
Water vapor,Digital terrestrial broadcasting waves,Propagation delay
Frequent heavy-rain events in Japan have heightened the need for precipitation forecasts with sufficient lead time. To accurately predict convective cloud formation, monitoring water vapor variations in the lower atmosphere—specifically within several hundred meters above the ground—is desired, in addition to the vertical precipitable water observations1). A recently proposed method estimates water vapor fluctuations by exploiting the propagation delay of digital terrestrial broadcasting waves2). Previous studies have shown that delay variations inferred from surface meteorological measurements exhibit good agreement with those derived from this technique2). The present study focuses on assessing the applicability of this approach in urban environments, where numerous reflecting structures introduce multiple peaks in the delay profile3). During frequency offset correction, selecting a peak associated with an unintended reflector can lead to substantial measurement errors. Thus, establishing a robust procedure for determining the reflection-wave arrival time is essential for stable long-term operation in such environments.
This study, estimates water vapor variations using a reflection method in which a structure located opposite the transmitter serves as the reflector. One Yagi-Uda antenna receiving the direct wave from Tokyo Skytree and two identical antennas (A and B) receiving reflected waves are installed at the Chiba Institute of Technology. Antennas A and B (~5 m apart) combine their signals with the direct-wave signal before input to the observation system. The system records 10-s averaged delay profiles and the phase of the reflection peak the delay relative to the direct wave.
Because of the frequency offset between the transmitter and receiver reference clocks, the arrival time of the direct wave gradually drifts. While the direct-wave arrival time remains within a preset range, recording continues; otherwise observation is suspended for frequency correction and then resumed. The reflected wave peak position is estimated through quadratic fitting of the delay-profile amplitude around a preset value, and the corresponding phase is derived via linear interpolation. This study compares the effects of two setting values used for reflected-wave peak search—(1) during continuous phase measurement and (2) upon resuming observation after frequency correction—on peak estimation accuracy and phase stability.
A scatter plot of the propagation delay per unit distance is generated from reflection peaks at 521 MHz observed by antennas A and B (preset 22.87 μs) from 20 Nov. 2024 to 16 Nov. 2025. The reflector is presumed to be a high-rise building located ~3.5 km from the receiving site. Although antennas A and B are co-located and pointed toward the same direction, substantial variability is seen in the scatter plot. To investigate this variability, the data were classified based on the absolute difference between the measured peak and the preset value: (a) ≦0.4 μs, (b) ≦0.3 μs, (c) ≦0.2 μs, and (d) ≦0.1 μs. A notable reduction in scatter is observed for categories (c) and (d), along with an improvement in the correlation coefficient. Furthermore, the slope of the least-squares regression approaches unity, confirming close agreement between the propagation delays measured by antennas A and B. Considering the 6 MHz bandwidth of digital terrestrial broadcasting and the resulting delay-profile time resolution of ~0.17 μs, categories (c) and (d) are interpreted as cases where both antennas captured the same reflector, whereas categories (a) and (b) include contributions from different reflecting surfaces.
References: 1) Japan Meteorological Agency, https://www.jma.go.jp/jma/kishou/know/yohokaisetu/senjoukousuitai_ooame.html (accessed 2026.2.17), 2) Kawamura et al., Radio Science, 52, 367-377, 2017. 3) Kon et al., Proceedings of 2025 Annual Conference, Japan Society of Hydrology and Water Resources, PS-1-50, 2025.
This study, estimates water vapor variations using a reflection method in which a structure located opposite the transmitter serves as the reflector. One Yagi-Uda antenna receiving the direct wave from Tokyo Skytree and two identical antennas (A and B) receiving reflected waves are installed at the Chiba Institute of Technology. Antennas A and B (~5 m apart) combine their signals with the direct-wave signal before input to the observation system. The system records 10-s averaged delay profiles and the phase of the reflection peak the delay relative to the direct wave.
Because of the frequency offset between the transmitter and receiver reference clocks, the arrival time of the direct wave gradually drifts. While the direct-wave arrival time remains within a preset range, recording continues; otherwise observation is suspended for frequency correction and then resumed. The reflected wave peak position is estimated through quadratic fitting of the delay-profile amplitude around a preset value, and the corresponding phase is derived via linear interpolation. This study compares the effects of two setting values used for reflected-wave peak search—(1) during continuous phase measurement and (2) upon resuming observation after frequency correction—on peak estimation accuracy and phase stability.
A scatter plot of the propagation delay per unit distance is generated from reflection peaks at 521 MHz observed by antennas A and B (preset 22.87 μs) from 20 Nov. 2024 to 16 Nov. 2025. The reflector is presumed to be a high-rise building located ~3.5 km from the receiving site. Although antennas A and B are co-located and pointed toward the same direction, substantial variability is seen in the scatter plot. To investigate this variability, the data were classified based on the absolute difference between the measured peak and the preset value: (a) ≦0.4 μs, (b) ≦0.3 μs, (c) ≦0.2 μs, and (d) ≦0.1 μs. A notable reduction in scatter is observed for categories (c) and (d), along with an improvement in the correlation coefficient. Furthermore, the slope of the least-squares regression approaches unity, confirming close agreement between the propagation delays measured by antennas A and B. Considering the 6 MHz bandwidth of digital terrestrial broadcasting and the resulting delay-profile time resolution of ~0.17 μs, categories (c) and (d) are interpreted as cases where both antennas captured the same reflector, whereas categories (a) and (b) include contributions from different reflecting surfaces.
References: 1) Japan Meteorological Agency, https://www.jma.go.jp/jma/kishou/know/yohokaisetu/senjoukousuitai_ooame.html (accessed 2026.2.17), 2) Kawamura et al., Radio Science, 52, 367-377, 2017. 3) Kon et al., Proceedings of 2025 Annual Conference, Japan Society of Hydrology and Water Resources, PS-1-50, 2025.