Detecting wet surfaces using near infrared lighting

We propose a system to detect wet surfaces using near infrared LED lighting and a conventional CCD camera. There is a sharp fall in the transmission of light through water for wavelengths longer than 920 nm. By detecting this transition it is possible to robustly detect a film of water lying on a surface. This paper considers surfaces that are impermeable, are not hydrophilic, and are sufficiently reflective (reflectivity, rho>0.4). A system is demonstrated that can detect water on a wide range of surfaces that meet these conditions.