An apparatus for measuring parameters, such as moisture content or basis weight, of a fibrous web, e.g. paper or non-wovens, comprises optical elements and a wavelength selection device for selectively directing a beam of electromagnetic radiation comprising wavelengths in at least the mid infrared (MIR) spectral range through the web; an element, such as a beam stop, arranged in the path of electromagnetic radiation emerging from the web, for separating directly transmitted from scattered electromagnetic radiation; a collector for collecting the scattered radiation; and at least one detector for detecting the scattered radiation collected by the collector.