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Kolláth, Z., Cool, A., Jechow, A., Kolláth, K., Száz, D., & Tong, K. P. (2020). Introducing the Dark Sky Unit for multi-spectral measurement of the night sky quality with commercial digital cameras. Journal of Quantitative Spectroscopy and Radiative Transfer, 253, 107162.
Abstract: Multi-spectral imaging radiometry of the night sky provides essential information on light pollution (skyglow) and sky quality. However, due to the different spectral sensitivity of the devices used for light pollution measurement, the comparison of different surveys is not always trivial. In addition to the differences between measurement approaches, there is a strong variation in natural sky radiance due to the changes of airglow. Thus, especially at dark locations, the classical measurement methods (such as Sky Quality Meters) fail to provide consistent results. In this paper, we show how to make better use of the multi-spectral capabilities of commercial digital cameras and show their application for airglow analysis. We further recommend a novel sky quality metric the ”Dark Sky Unit”, based on an easily usable and SI traceable unit. This unit is a natural choice for consistent, digital camera-based measurements. We also present our camera system calibration methodology for use with the introduced metrics.
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Ayuga, C. E. T., & Zamorano, J. (2018). LICA AstroCalc, a software to analyze the impact of artificial light: Extracting parameters from the spectra of street and indoor lamps. Journal of Quantitative Spectroscopy and Radiative Transfer, 214, 33–38.
Abstract: The night sky spectra of light-polluted areas is the result of the artificial light scattered back from the atmosphere and the reemission of the light after reflections in painted surfaces. This emission comes mainly from street and decorative lamps. We have built an extensive database of lamps spectra covering from UV to near IR and the software needed to analyze them. We describe the LICA-AstroCalc free software that is a user friendly GUI tool to extract information from our database spectra or any other user provided spectrum. The software also includes the complete color database of paints from NCS comprising 1950 types. This helps to evaluate how different colors modify the reflected spectra from different lamps. All spectroscopic measurements have been validated with recommendations from CIELAB and ISO from NCS database.
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Baddiley, C. (2021). Light pollution colour changes at MHAONB, from distant town conversions to blue-rich LED lighting, implications for rural UK skies. Journal of Quantitative Spectroscopy and Radiative Transfer, in press, 107574.
Abstract: The sky in the Malvern Hills Area of Outstanding Natural Beauty (MHAONB) has been monitored continually since 2012, when a dark sky survey of the area was carried out commissioned by Malvern Hills Conservators. Ever since then at F.C.Mathon, the sky brightness has been measured continually, in the last few years at minute intervals in all weathers. On the darkest of nights, a fisheye lensed camera was used at the same intervals. There is a trend in brightness distribution and colour changes on the sky, especially towards the horizon, with clearly separated bright sky domes. The sky quality meter (SQM) photometry data near zenith does not show any great change. In 2015, Malvern Hills Conservators commissioned the author for modelling of the effect on the MHAONB sky, of the ongoing blue rich LED re-lighting throughout Herefordshire.
The SQM photometry shows the sky brightness are very weather dependent; and the camera shows colour changes from orange-pink to blue-rich LEDs. Besides the trend over recent years to blue white from orange, changes can occur over hours or even minutes, depending on cloud cover over individual towns on or beyond the horizon, and local humidity levels. It can vary from orange to blue and red. Clear skies can vary in overall colour from one night to another and brightness falls overnight. This is shown in isophotes and accurate profile curve fitting. The effect of 2020 lockdown is included. A measurement was made of the clear air back scatter ratio from a known luminance source which can be used to estimate the sky visibility degradation from any planned lighting scheme.
For the rural UK, the Milky Way is only 20% contrast to background at zenith on the darkest nights, (MHAONB 21.10 mag.arcsec-2), doubling the road light level across Europe would make it invisible.
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Baddiley, C. (2018). Light pollution modelling, and measurements at Malvern Hills AONB, of county conversion to blue rich LEDs. Journal of Quantitative Spectroscopy and Radiative Transfer, 219, 142–173.
Abstract: The introduction of blue rich colour, Correlated-Colour-Temperature (CCT) 6000K road lighting could increase skyglow significantly compared with CCT 3000K types, if the blue content reaches the sky.
Highways England have a policy for lighting specification on motorways advised by the author's work. This is a categorised environmental impact point system of summed brightness as a function of angle from vertically down to the cut off angle; but with no CCT limitation.
Modelling was done for Malvern-Hills Area-of-Outstanding-Natural-Beauty (MHAONB), for the nighttime environmental impact of the LED replacement of Low-Pressure-Sodium throughout Herefordshire. The study was extended to include High-Pressure-Sodium and to LEDs at several CCTs, for the same Photopic ground illuminance.
Dark-Sky-Survey geographic location results for the MHAONB (2012) are described. Near-Zenith sky brightness photometry became continuous from 2016 at 2 minute intervals in all weathers, not just clear nights, with a networked calibrated Unihedron Lensed Sky Quality Meter (LSQM). Samples were also taken of all-sky camera images, corrected for vignetting and near-Zenith calibrated with the LSQM, to study weather effects, Milky Way contribution, and Herefordshire lighting conversion to blue-rich LEDs (2013-15), compared with the less converted Severn valley direction.
Time-plots and histogram analysis showed a small reduction in brightness (2012-2018), 0.1 mag.arcsec−2. Most variation is from increased sampling of distant cloud cover effects. Mist or low cloud on the horizon obscures light sources beyond reducing local skyglow, while high cloud reflects, increasing clear sky brightness. The Milky Way is critically 20% above background. Darkest periods near Zenith reach 21.1 mag.arcsec−2, to 21.2 after rain or surrounding low-cloud or poor-visibility. Clear-sky brightness decreases into early hours (∼0.03 mag.arcsec−2/hr); dimming effects were not seen.
The Zenith brightness is still set by distant cities, while towards the horizon, commercial and private uncontrolled non-directional LED lighting is increasing, negating the improvements in road lighting.
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Ges, X., Bará, S., García-Gil, M., Zamorano, J., Ribas, S. J., & Masana, E. (2018). Light pollution offshore: Zenithal sky glow measurements in the mediterranean coastal waters. Journal of Quantitative Spectroscopy and Radiative Transfer, 210, 91–100.
Abstract: Light pollution is a worldwide phenomenon whose consequences for the natural environment and the human health are being intensively studied nowadays. Most published studies address issues related to light pollution inland. Coastal waters, however, are spaces of high environmental interest, due to their biodiversity richness and their economical significance. The elevated population density in coastal regions is accompanied by correspondingly large emissions of artificial light at night, whose role as an environmental stressor is increasingly being recognized. Characterizing the light pollution levels in coastal waters is a necessary step for protecting these areas. At the same time, the marine surface environment provides a stage free from obstacles for measuring the dependence of the skyglow on the distance to the light polluting sources, and validating (or rejecting) atmospheric light propagation models. In this work we present a proof-of-concept of a gimbal measurement system that can be used for zenithal skyglow measurements on board both small boats and large vessels under actual navigation conditions. We report the results obtained in the summer of 2016 along two measurement routes in the Mediterranean waters offshore Barcelona, travelling 9 and 31.7 km away from the coast. The atmospheric conditions in both routes were different from the ones assumed for the calculation of recently published models of the anthropogenic sky brightness. They were closer in the first route, whose results approach better the theoretical predictions. The results obtained in the second route, conducted under a clearer atmosphere, showed systematic differences that can be traced back to two expected phenomena, which are a consequence of the smaller aerosol content: the reduction of the anthropogenic sky glow at short distances from the sources, and the slower decay rate of brightness with distance, which gives rise to a relative excess of brightness at large distances from the coastline.
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