A method of characterizing a wet paint layer of a painted body by paint layer parameters based on fitting to a physical model is provided. The method is carried out by a sensor system in a non-contact manner, the sensor system including an emitter system for emitting THz radiation, a detector system for detecting THz radiation, and a processing unit operationally coupled to the emitter system and the detector system. The method includes: Emitting, by the emitter system, a THz radiation signal towards the painted body such that the THz radiation interacts with the wet paint layer, the wet paint layer having not yet finished a drying process during which the wet paint layer becomes a dry paint layer; and Detecting, by the detector system, a response signal being the detected THz radiation signal having interacted with the wet paint layer.