Imaging and mapping the impact of clouds on skyglow with all-sky photometry

Andreas Jechow,Henk Spoelstra,Salvador J Ribas,Zoltán Kolláth,Christopher C M Kyba,Franz Hölker

doi:10.1038/s41598-017-06998-z

Abstract

Artificial skyglow is constantly growing on a global scale, with potential ecological consequences ranging up to affecting biodiversity. To understand these consequences, worldwide mapping of skyglow for all weather conditions is urgently required. In particular, the amplification of skyglow by clouds needs to be studied, as clouds can extend the reach of skyglow into remote areas not affected by light pollution on clear nights. Here we use commercial digital single lens reflex cameras with fisheye lenses for all-sky photometry. We track the reach of skyglow from a peri-urban into a remote area on a clear and a partly cloudy night by performing transects from the Spanish town of Balaguer towards Montsec Astronomical Park. From one single all-sky image, we extract zenith luminance, horizontal and scalar illuminance. While zenith luminance reaches near-natural levels at 5 km distance from the town on the clear night, similar levels are only reached at 27 km on the partly cloudy night. Our results show the dramatic increase of the reach of skyglow even for moderate cloud coverage at this site. The powerful and easy-to-use method promises to be widely applicable for studies of ecological light pollution on a global scale also by non-specialists in photometry.

Highlights

Artificial skyglow is the part of artificial light at night (ALAN) that is scattered or reflected within the atmosphere and directed back towards the Earths surface[1]
The images are shown in Hammer–Aitoff equal area projection and were calculated from all-sky images obtained with a commercial digital single lens reflex (DSLR) camera
Zenith luminance observed on clear nights can underestimate the degree to which a site is exposed to skyglow under all weather conditions

Summary

Introduction

Artificial skyglow is the part of artificial light at night (ALAN) that is scattered or reflected within the atmosphere and directed back towards the Earths surface[1]. Studies of skyglow in the context of ELP are very sparse, with the exemption of seminal work by Moore on zooplankton[18] This is mainly owing to the fact that the status-quo of light at night in general and of ALAN (including skyglow) is not well known. As a basis for this, it is essential to first fully know the availability of all light at night in the environment[26] This should include unpolluted sites as well as heavily polluted sites and all states in between, at best at all weather conditions. Atmospheric conditions and especially clouds prevent any satellite data acquisition, rendering it a clear-weather-only method

Methods

Results

Discussion

Conclusion