5:15 PM - 7:15 PM
[STT42-P11] Experimental Study on the Possibility of Observing Fireworks by DAS Using Overhead Lines
Keywords:DAS, Firework, Infrasound
Distributed Acoustic Sensing (DAS) techinique on fiber optic sensing is showing great potential in seismology in that it enables wide-area and high-density observations. While buried optical fibers are preferred for such seismic monitoring, there are many optical fiber cables installed overhead in Japan. Although overhead fibers seem to be not suitable for detecting underground signals, they may have a potential to detect the signals in the air. In particular, the measurement of aerial signals using pre-existing overhead or surface-laid fibers has the potential to renew the observation of air pressure waves, which is considered to be one of the ways to detect the eruption in volcanology.
This study aims to investigate the feasibility of aerial signal detection using DAS by conducting two observational experiments focusing on signals from fireworks. The first experiment utilized an existing overhead fiber optic cable from a cable television network in an urban area (total length: approx. 2.3 km, within 2 km of the fireworks launch site) for DAS measurements. The objective was to assess the signal-to-noise ratio at which signals of a scale comparable to fireworks can be detected using existing overhead fiber. The second experiment involved newly installed fiber optic cables (total length: approx. 430 m) at an experimental site (approximately 5 km from the fireworks launch site) under three different conditions: buried (at depths of approx. 50 cm, 30 cm, and 10 cm), surface-laid, and overhead (at approx. 1 m height). Additionally, at the same site, a 3-component 2-Hz seismometer (CDJ-S2C-2, Chongqing Geological Instrument Factory), three infrasound sensors (prototype developed by Keio University’s Takahashi Laboratory, Wada & Takahashi, 2020), and a microbarometer (KAP-4, Krone Co., Ltd.) were deployed. The purpose of these simultaneous multi-sensor measurements was to examine the impact of fiber installation conditions on the observed signals. In both experiments, DAS measurements were conducted using an interrogator and software provided by NEC Corporation, with a Pulse Frequency of 500 Hz and a Monitoring Step of 3.2 m.
This paper presents the results of the observations conducted in an urban area on February 15 and at the experimental site on February 16 for firework events. The observed waveforms were processed using a bandpass filter ranging from approximately 1 Hz to 10 Hz. On both days, the weather conditions were similar, with a temperature of approximately 2 °C and a surface wind speed of about 2 m/s under weak wind conditions. At the experimental site (approximately 5 km from the launch point), the infrasound sensor recorded a significant signal of 0.1 Pa, while the seismometer detected a velocity of 3 μm/s during the firework launch. In the urban area measurement on February 15, a signal that appears to propagate at the speed of sound was detected. Meanwhile, in the February 16 experiment using optical fibers at the test site, it was confirmed that different waveforms were recorded depending on the fiber installation conditions. However, in both cases, only basic signal processing techniques (waveform filtering and averaging with neighboring measurement points) were applied, and it was difficult to definitively identify DAS waveforms as originating from fireworks. Future studies will not be limited to the low-frequency domain but will also consider higher frequency ranges to further evaluate the feasibility of detecting firework sound waves.
Acknowledgement
We sincerely appreciate Kawaguchiko Cable Television Co. Ltd. for allowing us to use a part of their fiber-optic cable network for the observation in the urban fiber.
This study aims to investigate the feasibility of aerial signal detection using DAS by conducting two observational experiments focusing on signals from fireworks. The first experiment utilized an existing overhead fiber optic cable from a cable television network in an urban area (total length: approx. 2.3 km, within 2 km of the fireworks launch site) for DAS measurements. The objective was to assess the signal-to-noise ratio at which signals of a scale comparable to fireworks can be detected using existing overhead fiber. The second experiment involved newly installed fiber optic cables (total length: approx. 430 m) at an experimental site (approximately 5 km from the fireworks launch site) under three different conditions: buried (at depths of approx. 50 cm, 30 cm, and 10 cm), surface-laid, and overhead (at approx. 1 m height). Additionally, at the same site, a 3-component 2-Hz seismometer (CDJ-S2C-2, Chongqing Geological Instrument Factory), three infrasound sensors (prototype developed by Keio University’s Takahashi Laboratory, Wada & Takahashi, 2020), and a microbarometer (KAP-4, Krone Co., Ltd.) were deployed. The purpose of these simultaneous multi-sensor measurements was to examine the impact of fiber installation conditions on the observed signals. In both experiments, DAS measurements were conducted using an interrogator and software provided by NEC Corporation, with a Pulse Frequency of 500 Hz and a Monitoring Step of 3.2 m.
This paper presents the results of the observations conducted in an urban area on February 15 and at the experimental site on February 16 for firework events. The observed waveforms were processed using a bandpass filter ranging from approximately 1 Hz to 10 Hz. On both days, the weather conditions were similar, with a temperature of approximately 2 °C and a surface wind speed of about 2 m/s under weak wind conditions. At the experimental site (approximately 5 km from the launch point), the infrasound sensor recorded a significant signal of 0.1 Pa, while the seismometer detected a velocity of 3 μm/s during the firework launch. In the urban area measurement on February 15, a signal that appears to propagate at the speed of sound was detected. Meanwhile, in the February 16 experiment using optical fibers at the test site, it was confirmed that different waveforms were recorded depending on the fiber installation conditions. However, in both cases, only basic signal processing techniques (waveform filtering and averaging with neighboring measurement points) were applied, and it was difficult to definitively identify DAS waveforms as originating from fireworks. Future studies will not be limited to the low-frequency domain but will also consider higher frequency ranges to further evaluate the feasibility of detecting firework sound waves.
Acknowledgement
We sincerely appreciate Kawaguchiko Cable Television Co. Ltd. for allowing us to use a part of their fiber-optic cable network for the observation in the urban fiber.