Abstract: Optical radiation sources functioning on different optical bands radiate on different optical bands and focus optical radiation on a region in a web surface as pulses in such a manner that illumination areas of the pulses overlap on the plane of the web. At most one optical radiation band is focused on the web from the direction of the normal. The spatial intensity distribution of at least one optical band differs from the uniform distribution and the intensity distributions of at least two different optical bands differ from one another in a predetermined manner. A camera forms still images of the web surface region on each optical radiation band. An image-processing unit determines the surface topography of the web on the basis of the images. In addition, a controller may control the paper manufacturing process on the basis of the determined surface topography.

Abstract: Optical radiation sources functioning on different optical bands radiate on different optical bands and focus optical radiation on a region in a web surface as pulses in such a manner that illumination areas of the pulses overlap on the plane of the web. At most one optical radiation band is focused on the web from the direction of the normal. The spatial intensity distribution of at least one optical band differs from the uniform distribution and the intensity distributions of at least two different optical bands differ from one another in a predetermined manner. A camera forms still images of the web surface region on each optical radiation band. An image-processing unit determines the surface topography of the web on the basis of the images. In addition, a controller may control the paper manufacturing process on the basis of the determined surface topography.