Raindrops keep falling on my windscreen

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.