This umbrella ‘listens’ to rain — for science

Someday, umbrellas may do more than just keep people dry. A researcher in the Netherlands has designed a simple sensor that “listens” to rain. And that sensor can turn a bumbershoot into a rain-measuring whiz.

Tools like this can let anyone measure the weather. That can help scientists make sure that satellites and radar systems that track storms are doing a good job.

“Rain radar is a beautiful way of seeing where rainfall is up in the air. But you never know where it hits the ground,” says Rolf Hut. He designed the umbrella sensor.

Researchers want to know how much rain makes it to the planet’s surface. Not all rain that falls from a cloud reaches the ground. And it can be difficult for radar and satellites to gauge that rain, particularly in cities. A host of big buildings can change how air — and rain — move during a storm. This is one reason that it can be pouring in one spot and barely sprinkling 10 to 20 blocks away.

It also explains why a single, expensive sensor — the kind that might be found at an official weather station — won’t give accurate city-wide data, Hut says. But by putting low-cost rain gauges into people’s hands, scientists can learn more about how much rainfall varies in these and other tricky-to-measure places.

Hut showed off his prototype umbrella at the European Geosciences Union General Assembly meeting in Vienna, Austria, in late April. He is a water-management researcher at Delft University of Technology in Delft, the Netherlands.

Eavesdropping on the rain

The unique sensor on Hut’s umbrella started as part of a project to design very-low-cost weather stations, including rain gauges, for use in Africa.

Researchers use rain gauges to figure out how much rain is falling, and how quickly. Some rain gauges are simple containers with markings on the side. Others have tipping buckets, which fill and empty as the rain falls. (Each time they pour out, they add a mark to an electronic tally.)

Direct measurement of water isn’t necessary for figuring out how much water has fallen. Sound also can convey such information. From the pitter-patter — or pounding — of rain on the roof, a person can estimate how much rain is falling. Hut and a colleague, along with several students, came up with a low-cost sensor that works in a similar way: It “listens” to the rain. Their sensor records the sound of each drop as it hits. That gauge can “hear” how big a raindrop is and how fast it’s falling. A computer can sum up those data to figure out how much rain lands over time. The whole system has a fancy name: acoustic disdrometer.

Hut came up with the idea to stick the same type of sensor on an umbrella when he was talking to kids about science. He showed them a photo of a policeman who was holding an umbrella and talking to a crowd in a microphone. Why not put the two together? He thought it could make a cool rainfall sensor.

Hut, who likes to tinker, used a few simple pieces to build his system. He bought a part called a piezoelectric disk. When this disk bends, it creates a tiny electric current. These types of disks are sometimes used to make buzzing alarms that wake people up in the morning. Many microphones also use them.

To make his device, Hut glued that disk onto a Winnie-the-Pooh umbrella. Then he took apart a hands-free cellphone headset and pulled out its microphone. He connected the pieces of the headset to the disk with wires. “If you then connect the Bluetooth headset wirelessly to your phone, then your phone starts listening to the vibrations in the [fabric] of your umbrella,” Hut explains.

Rutger van Iperen, who works for AMIS in Nieuwegein, the Netherlands, created a basic smartphone app. It analyzes the sound of the raindrops.

When a storm came through, Hut compared the umbrella’s new “ear” for rain to an official rain gauge on his balcony. And to his delight, he found the umbrella’s measurements were “pretty good.”

His next step is to refine the umbrella sensor to make it more accurate. He also plans to post details online in the next few weeks showing how anyone can turn an umbrella into a walking rain gauge. Search for “umbrella sensor” at www.instructables.com.

Small sensors help out

These little rain gauges that anyone can use are an example of citizen science. They offer the public a chance to gather data that researchers can use. They can also fill in gaps between the systems that collect data at scientific research stations, says Chris Kidd.

A satellite meteorologist, he studies weather and climate with the help of satellites. He works at the University of Maryland in College Park and nearby at NASA’s Goddard Space Flight Center in Greenbelt, Md.

At the same meeting in Vienna, Kidd presented research showing how few rain gauges today collect data. Add up the total number around the globe, he says, and they cover an area of between 120 and 3,000 square meters (around 1,300 square feet to perhaps ¾ of an acre). That range runs from an area smaller than a tennis court to a space covering about half the size of a soccer field.

Clearly, that’s not enough coverage to fully understand the most important thing that comes from rainfall: water.

“You use water throughout the day. You use water from the moment you get up to the moment you go to bed,” Kidd says. And it’s not just the water people drink and use in their homes. Water is a valuable resource. It irrigates farm fields and is used in making most things, from cars to books to computers. “Water is absolutely vital to all of us,” he observes.

For younger individuals who want to learn more about rainfall — or anything else — it is crucial to keep asking questions, says Hut. He also recommends playing around with devices and taking them apart to learn how they work (as long as kids have permission to do so).

Try putting together electronic ingredients and seeing what happens, Hut says — just like attempting to whip up a cake in the kitchen. Even kids can follow “recipes” developed by other experienced makers or from websites dedicated to making things, he says: “Technology is not just for grownups.”

Through that process, anyone who is curious can learn how to create his or her own inventions. And sometimes, one of the ingredients might be as simple as an umbrella.

Power Words

acoustic disdrometer    A device that uses sound to measure falling water.

acoustics    The science related to sounds and hearing.

app    Short for application. It’s a computer program designed for a specific task, often on a smartphone or tablet computer.

bumbershoot    Another word for umbrella, which some people think may be a combination of the words “umbrella” and “parachute”.

citizen science     Scientific research in which the public — people of all ages and abilities — participate. The data that these citizen “scientists” collect helps to advance research. Letting the public participate means that scientists can get data from many more people and places than would be available if they were working alone.

climate    The weather conditions prevailing in an area in general or over a long period.

electric current   A flow of charge, called electricity, usually from the movement of negatively charged particles, called electrons.

meteorologist    Someone who studies weather and climate events.

piezoelectricity     An electric discharge, often as a result of subtly deforming a crystal or crystalline material.

prototype    A first or early model of some device that still needs to be perfected.

sensor     A measurement device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. For example, a sensor might measure rain on a surface, and convert that to a signal to turn windshield wipers on. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly.

smartphone  A cell (or mobile) phone that can perform a host of functions, including search for information on the Internet.

weather     Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.