
Counting raindrops using mobile-phone towers - sohkamyung
https://www.economist.com/news/science-and-technology/21729740-rain-affects-signal-strength-which-means-you-can-measure-it-counting-raindrops
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anilakar
Back in 2002–2004 when DSL wasn't a commodity, a local ISP offered WLAN
access. We lived on a ridge and had a clean line of sight – some 2.6 km – to
one of the base stations so we set up a spare satellite dish with a peanut can
feed and were happy customers thereafter.

In the dry winter months the we had some 22 dB of signal-to-noise ratio and
during the summer months it fell to 15 ish dB. The link became unusable at
around 11 decibels of SNR, which we hit during heavy rain and fog. Just
looking at the link quality would tell you as much as peeking out of the
window.

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asafira
Are they really counting raindrops though, or just estimating rainfall
intensity?

I'm guessing the latter --- in which case, I'm not sure I'm a fan of the
sensationalism....

Regardless, is there a good resource for the modeling done in this?

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a_imho
They are not

 _Rain affects signal strength, which means you can measure it_

 _Some newer networks are sufficiently sensitive that they can detect humidity
and fog, both of which are predictors of imminent rain._

The idea is to use mobile towers as cheap weather stations/precipitation
radars especially in developing countries.

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Darthy
Full article: [http://archive.is/1E59I](http://archive.is/1E59I)

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aaron695
Mobile towers as radar for military use -

[http://www.telegraph.co.uk/news/uknews/1309952/Mobile-
teleph...](http://www.telegraph.co.uk/news/uknews/1309952/Mobile-telephone-
masts-can-detect-stealth-bombers.html)

~~~
twic
An article long on patriotism, short on detail! The boffins at Roke Manor are
presumably talking about passive radar:

[https://en.wikipedia.org/wiki/Passive_radar](https://en.wikipedia.org/wiki/Passive_radar)

Ah yes:

[https://www.electronicsweekly.com/news/archived/resources-
ar...](https://www.electronicsweekly.com/news/archived/resources-
archived/roke-manor-research-uses-mobile-phone-signals-to-make-cheap-2002-07/)

The most impressive passive radar idea i've heard is to use GPS signals as the
illumination. There is really no escape from those.

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mhb
Counting raindrops using umbrellas:
[https://news.ycombinator.com/item?id=15383330](https://news.ycombinator.com/item?id=15383330)

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crowbahr
Really interesting.

Didn't get the paywall everyone else did.

Here's the raw text:

NO ONE knows exactly how many people died in a series of mudslides that
happened in and near Freetown, the capital of Sierra Leone, on August 14th.
The upper estimates are more than a thousand. The areas swept away had not
been evacuated partly because no one knew how much rain had actually fallen
beforehand, laments Modeste Kacou, a rainfall expert at Félix Houphouët-Boigny
University in Abidjan, in nearby Ivory Coast. Rain gauges are sparse in Sierra
Leone. Satellites detect rainfall in the tropics, but estimates for small
areas are often inaccurate. Worse, these numbers are calculated hours after
the fact. Many countries therefore use cloud-scanning ground radar to measure
precipitation as it is happening, but Sierra Leone has no such radar.

Nor do many other poor countries. Ivory Coast has double the GDP per person of
Sierra Leone, but like most of west Africa, it also lacks precipitation radar.
Indeed, maintenance costs mean that the number of weather stations around the
entire world is shrinking, making it harder to forecast flash floods and
landslides even in some rich countries. It would be useful, therefore, if some
other way of measuring rainfall—preferably a cheap one that employs existing,
widespread equipment—could be devised. Fortunately, there is just such a
method, and it involves mobile-phone networks.

The basic insight is straightforward enough: rain weakens electromagnetic
signals. Many mobile-phone towers, especially in remote areas, use microwaves
to communicate with other towers on the network. A dip in the strength of
those microwaves could therefore reveal the presence of rain. The technique is
not as accurate as rooftop rain gauges. But, as Dr Kacou points out,
transmission towers are far more numerous, they report their data
automatically and they cost meteorologists nothing. He runs the Ivory Coast
operations of Rain Cell Africa, an effort paid for by the World Bank, the UN
Foundation, a charity, and the Institute for Development Research, which is
based in France, to map rainfall in parts of Africa using data donated by
Orange, a big telecoms firm, and Telecel Faso of Burkina Faso, a small one.
Had the system been running in Sierra Leone, he reckons evacuations could have
been carried out in time.

Rich countries are interested, too. A pilot project in the Netherlands a few
years ago produced promising results, but it has not yet been followed up.
This month officials in Gothenburg, Sweden, began to study rainfall maps
derived from data collected every ten seconds from 418 mobile-phone towers
owned by a firm called Hi3G. The hope is this will provide more accurate
estimates of rainwater about to slosh into the municipal waterworks, helping
managers to limit flooding and sewage overflows. Until now, the city has
relied on 13 rain gauges, backed up by radar sweeps of the sky that are
neither sufficiently frequent nor sufficiently precise, says Jafet Andersson,
a hydrologist behind the scheme at the Swedish Meteorological and Hydrological
Institute. Satellite data on rain in northern latitudes are so poor the agency
does not bother using them at all.

Though it is useful to know how much rain is falling right now, forecasting is
even better. Telecoms data promise to make this easier as well. Some newer
networks are sufficiently sensitive that they can detect humidity and fog,
both of which are predictors of imminent rain. Newer generations of mobile-
phone masts use shorter wavelengths in their transmissions, because these can
carry more data. Serendipitously, that also permits tinier amounts of water to
be detected, for moisture weakens short wavelengths more than long ones. Using
data from about 5,000 towers operated by three telecoms firms in Israel,
Pinhas Alpert of Tel Aviv University creates moisture maps that, he says, are
far more precise than those drawn with data from the Israel Meteorological
Service’s humidity gauges, of which there are fewer than 70.

The right wavelength Moreover, because transmission towers are so common,
predicting where rainclouds are being pushed by winds is easy and accurate,
notes Dr Andersson. Several governments in Africa and South-East Asia have
asked his team to set up rainfall-measurement networks for them. No deals have
yet been signed, though, for there is a stumbling block: money.

For the time being, telecoms companies are happy to let forecasters use their
data free of charge. As the value of such data becomes clearer, says Frédéric
Cazenave of the Institute for Development Research, that is likely to change.
Consider ClimaCell, a firm based in Boston, Massachusetts. In April ClimaCell
began selling forecasts based on phone-tower data which are so precise, it
claims, that its customers will be able to tell “if a plane, crane or game”
will get soaked.

The firm’s clients include three airlines, several sports leagues, a
construction company, a drone operator and a hedge fund (which uses weather
forecasts to make trades). It plans to offer its forecasts in India by the end
of this year, and to expand into ten more countries in 2018. If ClimaCell
pulls that off profitably, telecoms firms in both the rich and poor world are
likely to start demanding a slice of the action.

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bb88
Possibly a great story, too bad it's behind a paywall.

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marksomnian
Paywall.

