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Raindrops keep falling on my windscreen

Researchers from the University of Hanover have started an initiative that aims to use GPS-equipped cars to measure rainfall.

The most recent results of the RainCar project are now published in Hydrology and Earth System Sciences.

Rainfall can be very variable across different parts of a region such as Northern Germany. Conventional rain gauges are accurate, but are often distributed too sparsely to capture much of this variation.

‘If moving cars could be used to measure rainfall the network density could be improved dramatically,’ project-leader Uwe Haberlandt said in a statement.

To test their idea, they equipped a lab with a rain simulator to find out exactly how wiper speed relates to rainfall intensity.

Cars with different wiper systems were placed under the rain machine, which uses a sprinkler irrigation system with adjustable nozzles to simulate light to heavy rain.

In one set of experiments the team used the rain machine to test optical sensors that are installed in many modern cars to automate wipers. The sensors use a system of infrared laser beams that detect when drops of rain accumulate on the surface of the device. Each sensor reading corresponds to a specific amount of water, with more frequent readings corresponding to more intense rainfall.

‘The optical sensors measure the rain on the windshield in a more direct and continuous manner so, currently, they would be the better choice for rain sensors in cars,’ said Haberlandt.

The team could also test the effects of car movement on the measurements by placing the sensors on a rotating device, which simulates car speed, under the rain simulator. By knowing how the readings are affected by car speed, they can correct for this effect when using moving cars to measure rainfall.

But speed is not all that can alter the rain measurements, said Ehsan Rabiei, Haberlandt’s collaborator and the paper’s lead author.

‘Our experiments so far were carried out in an ideal and controlled environment. In nature there are external effects like wind, spray from other cars or shielding trees that can affect the readings, and rainfall characteristics are different from the rain simulator.’

‘The value of using moving cars to measure rainfall is not about a higher accuracy of rainfall measurements but about a much higher number of measurement points,’ said Haberlandt.

In a Hydrology and Earth System Sciences study published in 2010, two of the team members showed that a high number of less accurate rain gauges gives more reliable rainfall readings than a low number of very accurate devices.

The researchers are now working on field experiments using cars to measure real rainfall in and around Hanover. 

Readers' comments (1)

  • When I first read this and the pieces about wash & wearable metal textiles, I did check the date to make sure it was not April 1st!

    The possibilities are endless: when the rain starts to be measured accurately (via the programmable wig) it can surely activate a message home to take the washing in! Then during periods of drought the reverse: activate the sprinkler system to keep the lawns nice and green.

    I would subscribe heartily to a system of data management which substituted the mindless 'cr*p' of so much of the meja (not of course our august organ) with material which might actually be valuable.

    Do I not recall that the earliest clerics (between the two rivers Tigris and Euphrates and the Nile) were those who had worked out from observations of the stars and planets when it was an august? (bit late!) time to plant next-years crops. They became the gurus of all important matters: presumably to ensure that the tythes that would keep them in food and power would be payable!
    So, nothing new there.
    Mike B

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