Cloud Detection using Night Sky Background Light at the Pierre Auger Observatory

Rejection of cloud-contaminated data is a complex and important process at the Pierre Auger Observatory, one which combines information from several sources, including IR cameras, lidars, and satellite imaging. With the deteriorating quality of the IR cameras and challenges in using other sources, we propose a new method. We use continuous detector monitoring measurements to build a large database of night sky background fluxes for each pixel across 27 telescopes. Using this database, we generate the expected background flux and define cloud rejection thresholds. Through a straightforward analysis we construct boolean cloud-contamination masks. We demonstrate some results of the analysis, including comparisons with cloud detected using infra-red observations.