Abstracts

To assess the negative effects of artificial light at night, measurement data are often necessary. These can be acquired from ground or satellite-based measurements. Satellite-based observations of artificial light have an advantage of global coverage. Since the launch of the Suomi National Polar-orbiting Partnership (S-NPP) satellite, the Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night Band (DNB) provides a tool for worldwide night time remote sensing for various applications, including artificial light. We used the data in year 2015 from the VIIRS-DNB sensor to study the angular distribution of artificial light in major cities and metropoles in Europe. Despite encountering some issues, for example low overflight rate with cloud-free sky condition, we are able to investigate the angular distributions of upwelling artificial light emission for 74 regions, almost all of which emit more light near the horizon. In comparison to satellite-based observations, ground-based measurements can acquire data more frequently. An international campaign studying variations of night sky at 44 worldwide locations was conducted in 2011 and 2012, measuring the night sky using broadband radiometers, the Sky Quality Meters (SQMs), and was the first time comparing ground-based night sky measurement in a unified analysis procedure. The presence of artificial light reverses the variation pattern of sky brightness at cloudy nights. Instead of darkening of night sky by blockage of extraterrestrial light sources, clouds backscatter the artificial light emitted from ground, brighting the night sky. Comparison with daytime aerosol measurement data did not yield a consistent relationship between the aerosol content and night sky brightness for the rural site in Cabauw, the Netherlands, but found the brightening of the night sky of Madrid with increasing atmospheric aerosol load. Long-term monitoring of the night sky enables us to observe the change in skyglow pattern over a long period. Two SQMs have been set up in a suburban site and a rural site in Bremen, Germany since December 2011. The night sky of the suburban site is found to be brighter during cloudy nights and becomes darker during the course of the night, which is typical for a light-polluted location. While instrumental issues cannot be ruled out, we found a decrease of sky brightness over a span of about 4.5 years, with a stronger decreasing trend at late hours of the night. For the rural site, the local public and domestic lightings are the dominating light source, contributing to the larger skyglow in the early hours of the night. However, with domestic and public lighting switched off as the night progresses, the variation pattern of the night sky is typical for a location with less light pollution, where the overcast sky is only slightly different in brightness from clear sky. It is suspected that this trend in the change of sky brightness originates from the gradual decrease of output of the public lighting system due to aging, while the progress replacing the publicAdvisors/Committee Members: Heygster, Georg (advisor), Notholt, Justus (referee), Rckmann, Ilja (referee).