Drivers on a rainy day regulate the speed of their windshield wipers according to rain intensity: faster in heavy rain and slower in light rain. (Agencies)
This simple observation has inspired researchers from the University of Hanover in Germany to come up with 'RainCars', an initiative that aims to use GPS-equipped moving cars as devices to measure rainfall.
Conventional rain gauges are accurate, but are often distributed too sparsely to capture much of this variation. Having good information about precipitation is important for flood prediction and prevention.
"If moving cars could be used to measure rainfall the network density could be improved dramatically," said project-leader Uwe Haberlandt.
Haberlandt said the idea for RainCars emerged during a brainstorming session between geoinformatics researchers and hydrologists. Now, with a lab equipped with a rain simulator, the researchers have been able to put their idea to the test.
They placed cars with different wiper systems under the rain machine, which uses a sprinkler irrigation system with adjustable nozzles to simulate light to heavy rain, to find out exactly how wiper speed relates to rainfall intensity.
In one set of experiments, an individual in the car adjusted the wiper speed manually, depending on the windscreen visibility.
"The experiments have shown that the front visibility is a good indicator for rainfall intensity," said Ehsan Rabiei, Haberlandt's collaborator and the paper's lead author.
In another 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.
"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," Haberlandt said.
The results of the project are published in the journal Hydrology and Earth System Sciences.
Drivers on a rainy day regulate the speed of their windshield wipers according to rain intensity: faster in heavy rain and slower in light rain.