Abstract: A measuring instrument for simultaneous in situ determination of the spectral scatting and absorption coefficient, which can also be called an extinction meter, has a modulated light source and an optical system encompassing the hemisphere; the optical system has a multiply folded ray path with a focal point in the volume to be measured, and through this system the measurement signal is projected to detectors. The scattering measurement signals, which are maximally enlarged in this way, are then separated from those for the absorption. The extinction meter also has not only an integrating nephelometer for monitoring purposes but also a transmission meter for low transmission factors. Because of the small three-dimensional size and the streamlined shape of the measuring portion of the extinction meter, the extinction meter can be carried in aircraft and surface vehicles.