4:15 PM - 4:30 PM
[MIS09-04] Development of a method for estimating the location of lightning strikes using sound waves
★Invited Papers
Keywords:Lightning strike, Estimation of lightning strike location, Sound wave observation, Low-cost lightning strike observation equipment
Current lightning strike location data released in Japan is often provided in meshes that are more than 1km long, and even companies that provide it have an estimation error about 300m. Since there is no location accuracy of less than several tens of meters that can identify whether a lightning strike has caused damage to a building. If household goods are damaged, it may be difficult to distinguish the damage from time-related deterioration, wear and tear, or general malfunction, which may lead to problems with insurance coverage.
The reason why the accuracy of the lightning strike position is limited to the above is that the lightning strike position is derived from the difference in the arrival speed of electromagnetic waves generated during lightning strikes, and these waves are not points but three-dimensionally spread out. On the other hand, there is a recent report that the position of a lightning strike was estimated with an accuracy of more than ten meters, and in that previous study, sound waves were used to estimate the position of the lightning strike. The principle is that the low-frequency sound at the time of a lightning strike is observed at three points, and the position of the lightning strike is estimated from the difference in the time of observation. However, the reason why a positional accuracy of more than ten meters was achieved was because the condition of estimating the diminishing rate of temperature due to altitude differences in a narrow area of about 12 km in a mountainous region was met. It is not obvious whether the accuracy of this method of estimating the location of lightning strikes in urban areas, where temperatures vary locally by more than 2 degrees Celsius, can achieve an accuracy of more than ten meters.
The final objective of this research is to develop a method for estimating the location of lightning strikes using sound waves that can achieve an estimation accuracy of 10-20m in urban areas with large local temperature differences. In order to achieve this goal, we developed multiple devices that can observe multiple points of sound waves, electromagnetic waves of lightning as the time of occurrence 0, and temperature. At the same time, we aimed to reduce the cost of the measurement equipment (less than 20,000 yen per unit), so that the distance to the lightning strike point could be calculated without installing a GPS module. However, natural lightning strikes are not suitable for testing the accuracy of the developed device because it is not possible to know the exact point and time of occurrence, and the points of occurrence of lightning strikes are frequent and spread randomly in three dimensions. Therefore, the purpose of this research is to demonstrate the method of estimating the location of lightning strikes and the principle of the developed device by using fireworks whose time of occurrence (launch) and source are known in advance, and whose energy is known in the form of points.
For the development equipment, we used a Raspberry Pi 3 Model B, a high-sensitivity microphone amplifier kit (Akizuki Denshi, 50Hz~16kHz), an A/D converter, (10bit, mcp3008(Microchip)), and a temperature/humidity sensor (16bit, ±0.3°C error, SHT31-DIS( SENSIRION)) were used.
Using the three developed devices, we observed the sound waves of the fireworks, and from the video of the fireworks taken simultaneously with the sound waves, we considered the time when the fireworks exploded in the video to be the time of arrival of the electromagnetic wave in the lightning strike, and set it as time 0. The observation points were set up at three locations, about 490m, 2700m, and 4200m away from the fireworks launch point in order to make the distance from the launch point as different as possible. For the purpose of accuracy verification, only single fireworks were observed, and the point of fireworks burst was estimated using the time difference when the sound reached the observation equipment. Assuming a sampling frequency of 48 kHz, the estimation error of the distance to the point of firework burst from the time difference when the sound wave reached the device was 1m, 9m, and 50m for each point. By taking the temperature into account, we were able to confirm that the device is capable of identifying the location of lightning strikes with an error about 10 meters
The reason why the accuracy of the lightning strike position is limited to the above is that the lightning strike position is derived from the difference in the arrival speed of electromagnetic waves generated during lightning strikes, and these waves are not points but three-dimensionally spread out. On the other hand, there is a recent report that the position of a lightning strike was estimated with an accuracy of more than ten meters, and in that previous study, sound waves were used to estimate the position of the lightning strike. The principle is that the low-frequency sound at the time of a lightning strike is observed at three points, and the position of the lightning strike is estimated from the difference in the time of observation. However, the reason why a positional accuracy of more than ten meters was achieved was because the condition of estimating the diminishing rate of temperature due to altitude differences in a narrow area of about 12 km in a mountainous region was met. It is not obvious whether the accuracy of this method of estimating the location of lightning strikes in urban areas, where temperatures vary locally by more than 2 degrees Celsius, can achieve an accuracy of more than ten meters.
The final objective of this research is to develop a method for estimating the location of lightning strikes using sound waves that can achieve an estimation accuracy of 10-20m in urban areas with large local temperature differences. In order to achieve this goal, we developed multiple devices that can observe multiple points of sound waves, electromagnetic waves of lightning as the time of occurrence 0, and temperature. At the same time, we aimed to reduce the cost of the measurement equipment (less than 20,000 yen per unit), so that the distance to the lightning strike point could be calculated without installing a GPS module. However, natural lightning strikes are not suitable for testing the accuracy of the developed device because it is not possible to know the exact point and time of occurrence, and the points of occurrence of lightning strikes are frequent and spread randomly in three dimensions. Therefore, the purpose of this research is to demonstrate the method of estimating the location of lightning strikes and the principle of the developed device by using fireworks whose time of occurrence (launch) and source are known in advance, and whose energy is known in the form of points.
For the development equipment, we used a Raspberry Pi 3 Model B, a high-sensitivity microphone amplifier kit (Akizuki Denshi, 50Hz~16kHz), an A/D converter, (10bit, mcp3008(Microchip)), and a temperature/humidity sensor (16bit, ±0.3°C error, SHT31-DIS( SENSIRION)) were used.
Using the three developed devices, we observed the sound waves of the fireworks, and from the video of the fireworks taken simultaneously with the sound waves, we considered the time when the fireworks exploded in the video to be the time of arrival of the electromagnetic wave in the lightning strike, and set it as time 0. The observation points were set up at three locations, about 490m, 2700m, and 4200m away from the fireworks launch point in order to make the distance from the launch point as different as possible. For the purpose of accuracy verification, only single fireworks were observed, and the point of fireworks burst was estimated using the time difference when the sound reached the observation equipment. Assuming a sampling frequency of 48 kHz, the estimation error of the distance to the point of firework burst from the time difference when the sound wave reached the device was 1m, 9m, and 50m for each point. By taking the temperature into account, we were able to confirm that the device is capable of identifying the location of lightning strikes with an error about 10 meters