3.1.3 Infrared-based sensor system for contactless detection of wetness and ice on surfaces

20. GMA/ITG-Fachtagung Sensoren und Messsysteme 2019
2019-06-25 - 2019-06-26
Nürnberg, Germany
3.1 Infrarotsensoren
L. Tharmakularajah, J. Döring, L. Friedrich, K. Krieger - ITEM Universität Bremen (Deutschland)
210 - 215


In order to differentiate between a wet and a dry road surface, the water film height is measured by using an infrared-based sensor system. With the help of different wavelengths it is also possible to distinguish between ice and water. In this article, a sensor system for determination of the physical state of water on different surfaces with infrared LEDs and one photodiode is presented. This shall serve as a basis for the calculation of the road condition. Here, emitted and reflected signals of five different infrared emitters are acquired with an infrared receiver. In commercial sensors this method (with one emitter) is used to determine a distance. At a constant distance, different intensities for the reflected signal are measured depending on the color and texture of the surface. Similar sensor systems work with a broadband light, usually a halogen lamp, and several photodiodes. This type is more cost-intensive and not robust enough for the desired application. The transmission spectrum of water shows that light is absorbed little at a wavelength of 900 nm and strongly at a wavelength of about 1400 nm – 1500 nm. Therefore, the intensity depends not only on the material surface, but also on the wavelength of the transmitting and receiving diode. In order to distinguish between ice and water, the wavelengths 1450 nm and 1550 nm are compared, which is shown in this article by the measurements. In ice, the infrared light is more strongly absorbed at 1550 nm and less absorbed at 1450 nm.