Abstract: A method and an apparatus (15) for computer-implemented determination of physical properties of a porous layer (1) present on a surface of a substrate. The physical properties include at least a layer thickness (d) of the layer, a porosity (p) of the layer and a roughness (r) of the layer at an interface (9) with the substrate supporting the layer. The method includes recording a reflectance curve (39) concerning light (25) irradiated onto the porous layer within a wavelength range in which the porous layer is largely transparent, setting a predetermined roughness start value, setting a porosity start value based on knowledge concerning a manufacturing process for forming the porous layer, setting a layer thickness start value based on an evaluation of periodic fluctuations of reflectance intensities within the recorded reflectance curve, and determining the physical properties of the porous layer by computer-implemented fitting of the recorded reflectance curve using a non-linear least squares method.