Remote optical sensor for real-time residual salt monitoring on road surfaces

We report on an optical sensor for remote residual dry salt (NaCl) monitoring, with applications in road winter maintenance. The novelty of the sensing principle is the simultaneous measurement of the amplitude and decay time of the natural fluorescence of salt using synchronous detection. We present the characterisation of the luminous properties of salt that allow a sensor design with high sensitivity and stable measurements that match the requirements for the intended applications (concentrations below 20 g/m2). The proposed sensor system has a compact design and short response time, capable of being mounted on-board maintenance vehicles for real-time road condition assessment.