Abstract: According to an example aspect of the present invention, there is provided an apparatus comprising a normalized surface condition monitoring sensor, and a processing unit comprising at least one processing core, at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processing core, cause the apparatus at least to process surface data based on a real time position of the apparatus to obtain calibration of the surface condition monitoring sensor, wherein values of the surface data originate from at least one normalized surface condition monitoring system, and wherein at least some of the values of the surface data are associated with position information.

Abstract: A method and apparatus for calibrating an optical surface condition monitoring system (1). Light beams at different wavelengths (?1, ?2) 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 and no dry calibration plate or dry spot of the target surface (8) is required.