CALIBRATING AN OPTICAL SURFACE CONDITION MONITORING SYSTEM

According to an example aspect of the present invention, there is provided a method of calibrating an optical surface condition monitoring system (1). Light beams at different wavelengths (λ1, λ2) are emitted to a reference substrate (2) at different distances (L1, L2) as well as to sample substrates (5) at a specific distance (Lspecific). Subsequently, ratios between the signals scattered back from the reference substrate (2) and the signals scattered back from the sample substrates (5) are calculated. Then, input data regarding a measurement distance (Lmeasurement) between a target surface (8) to be monitored, for example a road, and the receiver (3) of the system (1) is provided. Further, a preset program is selected. Dry calibration of the system (1) can then take place based on the calculated ratios, the measurement distance (Lmeasurement) and the selected program. Dry calibration can be calculated without having to perform an actual dry calibration in the field. No dry calibration plate or dry spot of the target surface (8) is required for calibration according to the present invention.