In the past few years, several active instruments put in orbit have led to significant insights regarding the spatial distribution of clouds. Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) \cite{Winker_2010}, bla bla. CALIOP cannot penetrate optically thick clouds, and thus cannot always document the entire vertical profile of cloud fraction. However, this does not impair its ability to retrieve whether a given column of atmosphere contain clouds or not, with a high horizontal resolution and a sensitivity to optically thin clouds unmatched by most passive sensors. CALIOP is therefore a reliable source for documenting the overall cloud fraction and it has been often used so in recent years [bla bla et al. 2012, 2013 etc].