Gregory L Schuster, NASA Langley Research Center, Hampton, VA, United States, Oleg Dubovik, Laboratoire d'Optique Atmosphérique, CNRS/University of Lille, Lille, France, Antti Arola, Finnish Meteorological Institute, Helsinki, Finland, Tom Eck, USRA, Greenbelt, United States and Brent Holben, NASA Goddard Space Flight Center, Greenbelt, MD, United States