Analyzing night illumination in dependency of cloud coverage and altitude.

Despite the publication of a large number of scientific studies in recent years, the impact of clouds on night illumination remains inconclusive. It is also unclear how clouds affect the ever-increasing prevalence of artificial lighting and the subsequent brightening of the night sky. There are many reasons for this uncertainty. Often, the altitude at which the clouds are located is unknown. Furthermore, different measurement equipment is used, which makes it difficult to compare measurements. Additionally, sufficient measurements must be available, as data can vary considerably within a single night and from night to night. To address these issues, Fraunhofer IOSB has conducted measurements in the photopic visual (380-780 nm) and short-wave infrared (800-1700 nm) spectral ranges. These measurements reveal significant variability in terms of cloud coverage and altitude. Comparing these measurements with others has shown that, ultimately, a hemispheric measurement of night illumination combined with the simultaneous determination of cloud coverage and altitude is necessary to draw meaningful conclusions about the influence of artificial lighting on night illumination.