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Tokyo Skytree radio waves may help predict localized heavy downpours

by Atsushi Kawamura

Kyodo

Radio waves emitted by Tokyo Skytree may help make it easier to predict a heavy downpour in the Tokyo metropolitan area by the time the capital hosts the 2020 Olympic Games, according to research by the Tokyo-based National Institute of Information and Communications Technology.

The transmission speed of radio waves for digital terrestrial broadcasting slows down when there is a large amount of water vapor in the atmosphere, according to Seiji Kawamura, senior researcher at the institute.

By analyzing the delay of radio waves transmitted by the world’s tallest tower, which is situated in Sumida Ward, it may be possible to find out how much water vapor is contained in the atmosphere in a specific area.

“We aim to put the system into practical use before the 2020 Tokyo Olympics,” Kawamura said.

He explained that the tower keeps transmitting radio waves while broadcasting and that the envisioned system can utilize existing frequencies without the need for a new transmission facility.

Under existing forecast systems, it is considered challenging to make an accurate projection of exactly when heavy rain will hit a relatively small area for a short period of time.

Such a prediction is important as exemplified in 2008 when heavy rain caused the Toga River in Kobe to rise quickly. Five people lost their lives in that incident.

The Geospatial Information Authority of Japan in Tsukuba, Ibaraki Prefecture, has separately observed the amount of atmospheric water vapor by using signals from satellite-based Global Positioning Systems.

The Meteorological Agency refers to data collected by the authority when making its forecasts. However, the authority’s system is only capable of observing the amount of vapor vertically.

“Since radio waves for digital terrestrial broadcasting send stronger signals than satellite radio waves, they would help us obtain more detailed data collected near the surface of the ground, where the air contains much vapor,” Kawamura said of the new system.

Kawamura’s team has already made receivers for the Skytree radio waves and has developed computer software to be used for analysis.

He said that the institute eventually plans to install receivers at many locations to predict the amount of atmospheric water vapor every 30 seconds every 5 km.

“We hope to launch a feasibility experiment by the end of this fiscal year,” Kawamura said.

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