According to The Asahi Shimbun, a Japanese research institute may have found a quicker and cheaper way to accurately predict localized rainstorms by measuring water vapor in the air through radio waves of digital terrestrial TV broadcasts.
The National Institute of Information and Communications Technology (NICT) plans to install its new system--the size of several dictionaries--at different locations across the Kanto region, including buildings, for more trial runs.
Radio waves travel more slowly in thicker water vapor, although the difference may seem minuscule. For example, a 1-percent increase in water vapor concentration causes a delay of 17 one-trillionths of a second when radio waves are received at a distance of 5 kilometers.
The NICT used computers to analyze radio waves from receivers installed at different locations to measure propagation delays, thereby estimating the water vapor content.
Doing so allows for quick identification of locations where water vapor is highly concentrated and localized heavy rainstorms are likely to occur.
Rain clouds gather in a matter of several minutes before causing the precipitation of a localized heavy rainstorm.
Even high-performance weather radars, which cost several hundred million yen (several million dollars) per unit, can observe such storms only after raindrops have formed in the air. This makes it difficult to catch signs ahead of time.
The NICT’s receiver-cum-analyzer used with the new technique is available for a combined cost of only about 1 million yen (US$9,000).
One idea being floated is to embed a similar device in household TV sets to allow pinpoint predictions of localized heavy rainstorms. Forecasts become more accurate with an increasing number of receivers, NICT officials said.
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