Driving in the rain
November 29, 2013

RainCars Initiative Could Use Moving Vehicles To Measure Precipitation

redOrbit Staff & Wire Reports - Your Universe Online

Inspired by drivers who alter the speed of their windshield wipers when precipitation becomes more or less intense, researchers from the University of Hanover in Germany have created RainCars - a new initiative that uses moving, GPS-equipped automobiles to measure rainfall.

The study authors, who detail the most recent results of their project in the open-access journal Hydrology and Earth System Sciences, explained that rainfall can vary greatly in some parts of the world, including northern Germany. While ordinary rain gauges prove accurate, they typically are too few and far apart to accurately represent such variation.

Having detailed data about precipitation amounts can often be essential for helping predict and prevent floods and other catastrophic events, project leader Uwe Haberlandt of the university’s Institute of Water Resources Management, Hydrology and Agricultural Hydraulic Engineering and his colleagues explained in a statement Thursday.

“If moving cars could be used to measure rainfall the network density could be improved dramatically,” Haberlandt said, adding that the concept of RainCars came about following a brainstorming session involving geoinformatics researchers and hydrologists. The basis of the project is the fact that there are currently over 40 million cars in Germany alone, as well as the increasing amount of automotive traffic all over the world.

Haberlandt and his colleagues tested their concept in a laboratory that included a rain simulator. The researchers placed cars with different types of wiper systems under the precipitation machine, which featured a sprinkler irrigation system that had adjustable nozzles and was capable of varying intensity from heavy to light rainfall amounts.

In one set of experiments, a person sitting in the car adjusted the wiper speed manually based on the windscreen visibility. Ehsan Rabiei, lead author of the paper, explained that while this test demonstrated that front visibility was “a good indicator for rainfall intensity,” the fact that the measurements required a person to manually adjust wiper speed suggests that it might be unreliable.

During a second set of experiments, Rabiei, Haberlandt and their associates used the rain machine to test the effectiveness of optical sensors that have been installed in many modern vehicles in order to automatically control wipers. These sensors utilize a system of infrared laser beams which detect when drops of rain accumulate on the device’s surface, which each sensor corresponding to a specific amount of water.

“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,” Haberlandt said. He and his colleagues are already working on field experiments involving taxis in Hanover, which could measure actual rainfall amounts throughout the city.

Furthermore, his team could also test the impact of car movement on these measurements by placing the sensors on a rotating device that simulates car speed and placing it under the rain simulator. Understanding how the measurements are altered by car speed can allow them to correct for the effect when using mobile cars to measure rainfall. However, the researchers also point out there are other factors that need to be considered.

“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,” Rabiei said. Haberlandt added that “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.”

Image 2 (below): A car tested under a rain simulator. Credit: www.ikg.uni-hannover.de, Daniel Fitzner