Measurement apparatus and method of paper web

A measurement apparatus of a moving paper web, wherein:

• the apparatus comprises an optical radiation source that is configured to output optical radiation toward a scattering element of the measurement apparatus;
• the scattering element is configured to scatter the optical radiation, and a transmitting surface of the scattering element is configured to direct the optical radiation in a scattered manner toward the moving paper web;
• a distance between said transmitting surface of the scattering element and a surface of the paper web is known, and the transmitting surface and a detector of the apparatus are on opposite sides of the paper web;
• the detector is configured to receive at least a part of the optical radiation, which is side-scattered from the moving paper web, the side-scattered optical radiation deviating by a predetermined angle from a direction that extends from the scattering element to the paper web, and reject the optical radiation that has passed directly through the moving paper web without scattering;
• the detector is configured determine a moisture value and a dry weight of the paper web on a basis of spectral information on the received optical radiation and the known distance.