Vain, Ants, Sanna Kaasalainen, Juha Hyyppä, and Eero Ahokas. 2012. “Calibration of Laser Scanning Intensity Data Using Brightness Targets”. Geodesy and Cartography 35 (3):77-81. https://doi.org/10.3846/1392-1541.2009.35.77-81.