In order to quickly grasp the risks of frequent heavy rains and sediment-related disasters, it is necessary to know how much it is raining, but in areas without rain gauges, the actual amount of rain is not known.


Under these circumstances, a demonstration experiment was conducted in Tsukuba City, Ibaraki Prefecture, in an attempt to estimate rainfall using "images" from cameras in rivers nationwide.

In an experiment conducted at a large facility at the National Research Institute for Earth Science and Disaster Prevention in Tsukuba City, rain from 15 mm to 300 mm per hour was reproduced step by step, almost the same as the one installed in a river. Take a picture of the rain with a resolution camera.



And depends on the National Institute for Land and Infrastructure Management Group to promote research, by rain strength,


▽ size and of raindrops,


▽ speed to drop


it,


since the distance visible to the naked eye, called the ▽ "visibility" is different,


the rainfall from there It means that it can be estimated.



The person in charge was checking the state of raindrops and "visibility" on the monitor while changing the intensity of rain.



About 2,300 rain gauges are installed on rivers and roads nationwide managed by the Ministry of Land, Infrastructure, Transport and Tourism, but there are about 14,000 cameras that monitor rivers, six times as many.



If this method is established, it is expected that heavy rainfall can be grasped faster than before by grasping the rain situation in areas with few rain gauges such as mountainous areas and supplementing the rainfall analyzed by radar. It means that.



Hiroaki Nakatani, Director of the Sediment Disaster Laboratory, National Institute for Land and Infrastructure Management, said, "If this technology is put into practical use, it will be possible to know how much rain is raining in the rivers near me. Especially in the mountains. There are few scales, and I want to make use of this technology. "

How do you estimate the amount of rainfall from the image?

In this experiment, the

amount of

rainfall is estimated by grasping the


distance "visibility" that can be seen with the naked eye and


the shape and size of rain "rain streaks" that change depending on how it descends


from

the

camera image.

Estimated from "visibility" during the day

The specific method differs greatly between daytime and nighttime.



First of all, "visibility" is used during the day.



According to the research group, the stronger the rain, the worse the visibility. For example, in the case of "extremely heavy rain" of 50 mm or more per hour, it becomes impossible to see beyond several tens of meters.



Also, in the case of "heavy rain" of 120 mm per hour, the visibility can be several meters at a stretch in the worst case, depending on the conditions such as sunshine and fog.



In the experiment, "visibility" is confirmed under various weather conditions such as fog and haze, and the data is learned by AI = artificial intelligence to determine the amount of rainfall.

Estimated from "rain streaks" at night

On the other hand, during the nighttime when the visibility is not clear, we use data such as the shape and size of rain that looks linear, which is called "rain streaks".



"Rain streaks" tend to be large when the rain is strong and fall faster, and vice versa when the rain is weak. To estimate.



However, although there are certain patterns in "visibility" and "rain streaks", they differ depending on the weather conditions at that time, so it is necessary to train AI to learn a large amount of data in order to estimate rainfall with high accuracy. , It means that it takes time to collect and learn data.



The research group hopes to further research data collection and image processing technologies in the future, and eventually improve the accuracy to the same level as rain gauges.

Verify "Visibility" with different rainfall

In the experiment on the 6th, we reproduced the rain of 60 mm, 120 mm, and even stronger 180 mm per hour, and verified the "visibility" of each.



In the definition of the Japan Meteorological Agency (JMA), in 1 hour,


▽ 50 mm or more, and rain of less than 80 mm is "very heavy rain"


▽ 80 millimeters or more of rain is classified as "ferocious rain",


both in the spray of water, one side per the It is said that it becomes whitish and visibility deteriorates.



In the experiment on the 6th, we installed walls of four colors such as green and brown, which were likened to forests and earth and sand, about 75 meters away.



▽ 60 mm "very heavy rain" can be distinguished slightly, but


▽ 120 mm "heavy rain" makes it difficult to distinguish colors, and


▽ 180 mm rain

makes it difficult to distinguish

colors. Even the distinction is almost impossible.



This experiment was conducted for 4 days while changing the light conditions assuming the sunlight, and in the future, the image data of the camera taken and the rainfall data actually dropped will be compared to determine the "visibility" and "rainfall". After analyzing the pattern, we will let AI = artificial intelligence learn.