Fortis Watch Cosmonautis Stratoliner Ceramic P.M. 401.26.31 LP.10. The stratosphere is part of the atmosphere surrounding the Earth. It is located between 15 and 50 kilometers above sea level. In contrast to the surrounding troposphere, the temperature increases from 60 degrees to degrees due to the ozone absorbed UV radiation, which converts electromagnetic radiation into heat. Already in the 60s, pilots of reconnaissance flights, such as the US with the Lockheed U 2, needed a reliable technique for flights over 20000 meters. The U stands for utility and was used as a camouflage, so that Russia did not suspect. Since these aircraft literally vanish from the radar, Fortis has assigned the model Stratoliner to the space watches.