Remote sensing of clouds with longwave infrared cameras at the Pierre Auger Observatory

Abstract

Knowledge of atmospheric conditions at the site of a cosmic ray observatory is important, especially for measurements made using the fluorescence technique. At the Pierre Auger Observatory in Argentina, an extensive network of meteorological instruments is dedicated to atmospheric monitoring, several of which are used for the remote sensing of night-time clouds. Clouds can be identified passively by detection of the thermal radiation they emit, and are often strong radiators at long-wave infrared wavelengths. As part of the University of Adelaide’s contribution to the Observatory, we have in- stalled four infrared cameras at the Observatory for cloud detection. The current generation cloud cameras are radiometric, and are sensitive to the 8–14 μm waveband. However, identifying clouds is not necessarily straight- forward as atmospheric water vapour also absorbs and emits radiation at these wavelengths. In this dissertation, I present the method that I use to identify clouds in our thermal images. Another major focus of my studies has been to calibrate our cameras. However, as they were already collecting data at the Observatory, the routines had to be developed remotely. These methods have been reproducible for each of our cameras, and could perhaps benefit other researchers in this field.