observation: Level 1 - Only signal to measurement algorithm used
see: Matthias V., Böckmann C., Freudenthaler V., Pappalardo G., Bösenberg J., Amiridis V., Amodeo A., Balis D., Boselli A., Chaykovski A., Chourdakis G., Comeron A., Delaval A., De Tomasi F., Eixmann R., Frioud M., Hagard A., Iarlori M., Komguem L., Kreipl S., Larchev¿¿que G., Matthey R., Mattis I., Papayannis A., Rizi V., Rocadenbosch F., Schneider J., Schumacher R., Shcherbakov V., Simeonov V., Wandinger U., Wang X. and Wiegner M., Lidar intercomparison on algorithm and system level in the frame of EARLINET. Max-Planck-Institut Report No. 337 (2002)