Measuring night sky brightness: methods and challenges. (January 2018)

• Record Type: Journal Article
• Authors: Hänel, Andreas; Posch, Thomas; Ribas, Salvador J.; Aubé, Martin; Duriscoe, Dan; Jechow, Andreas; Kollath, Zoltán; Lolkema, Dorien E.; Moore, Chadwick; Schmidt, Norbert; Spoelstra, Henk; Wuchterl, Günther; Kyba, Christopher C.M.
• Is Part Of: Journal of quantitative spectroscopy & radiative transfer. Volume 205(2018)
• Page Start: 278
• Page End: 290
• Publication Date: 2018-01
• Subjects: Atmospheric effects -- Site testing -- Light pollution -- Techniques: photometric -- Techniques: spectroscopic; Spectrum analysis -- Periodicals; Radiation -- Periodicals; Analyse spectrale -- Périodiques; Rayonnement -- Périodiques; Radiation; Spectrum analysis; Periodicals; 543.0858
• DOI: 10.1016/j.jqsrt.2017.09.008
• Languages: English
• ISSNs: 0022-4073

Abstract

Highlights: First comprehensive overview paper on techniques for measuring night sky brightness. Discussion of the strengths and weaknesses of 1d photometric, 2d photometric and spectroscopic techniques. Pros and cons of deriving long time series versus a comprehensive characterization of an astronomical site at a given time. Providing a set of reference values on night sky brightness, some of which are hard to find in the literature. Containing Examples of 2d maps as well as of spectra of the night sky. Abstract: Measuring the brightness of the night sky has become an increasingly important topic in recent years, as artificial lights and their scattering by the Earth's atmosphere continue spreading around the globe. Several instruments and techniques have been developed for this task. We give an overview of these, and discuss their strengths and limitations. The different quantities that can and should be derived when measuring the night sky brightness are discussed, as well as the procedures that have been and still need to be defined in this context. We conclude that in many situations, calibrated consumer digital cameras with fisheye lenses provide the best relation between ease-of-use and wealth of obtainable information on the night sky. While they do not obtain full spectral information, they are able to sample the complete sky in a period of minutes, with colour information in three bands. This is important, as given the current global changes in lamp spectra, changes in sky radiance observed only with single band devices may lead to incorrect conclusions regarding long term changes in sky brightness. The acquisition of all-sky information is desirable, as zenith-only information does not provide an adequate characterization of a site. Nevertheless, zenith-only single-band one-channel devices such as the "Sky Quality Meter" continue to be a viable option for long-term studies of night sky brightness and for studies conducted from a moving platform. Accurate interpretation of such data requires some understanding of the colour composition of the sky light. We recommend supplementing long-term time series derived with such devices with periodic all-sky sampling by a calibrated camera system and calibrated luxmeters or luminance meters.