Most satellite laser stations have used extermal terrestrial targets at distances from several hundred metres to kilometres for the determination of the calibration constant. The disadvantage of this method is the incomplete overlap of the transmitter and receiver angular fields and the necessity to monitor accurately the optical distance of the remote target. At Potsdam station, one year ago we introduced a very simple calibration link based on dual diffuse scattering, which can be easily attached in front of any laser radar. No optical components other than diffuse reflectors are used. The inherent attenuation is about 10^13, so that a 1000 : 1 additional filter is sufficient to reach the single photoelectron level. The method has been used for routing operations during the MERIT campaign and for investigating some error sources as well.