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Author |
Kotarba, A.Z.; Chacewicz, S.; Żmudzka, E. |
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Title |
Night sky photometry over Warsaw (Poland) evaluated simultaneously with surface-based and satellite-based cloud observations |
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Journal Article |
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Year |
2019 |
Publication |
Journal of Quantitative Spectroscopy and Radiative Transfer |
Abbreviated Journal |
Journal of Quantitative Spectroscopy and Radiative Transfer |
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Volume |
235 |
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95-107 |
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Keywords |
Skyglow |
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Abstract |
Light pollution is a widely distributed form of anthropogenic pollution that threatens both biodiversity and human health. One of the most popular indicators is known as night sky brightness (NSB), measured with photometric techniques. In the study, we report results of the very first, long-term photometric survey of NSB over Poland's capital, Warsaw, for 636 nights between 2014 and 2016 using a sky quality meter (SQM). Data were collected for all-weather conditions and, for the first time, we simultaneously use two independent sources of cloud amount data: surface-based (SYNOP) and satellite-based (Meteosat/SEVIRI). Results show that Warsaw is significantly polluted by light, with average NSB of 18.65 ± 0.06 magSQM/arcsec2 (15 times higher than unpolluted sky). Zenithal NSB is almost unaffected by moonlight. During astronomical nights, cloud cover was the dominant determinant of NSB, increasing by 7 times for overcast sky. In general, the sky brightened by ∼0.2 magSQM/arcsec2 for each 10% increase in cloud fraction. Satellite-based cloud amount data was found to be a very reliable alternative to traditional SYNOP observations. No statistically significant difference was found for average NSB calculated using satellite and SYNOP datasets. This finding is of particular importance, since the coverage of surface-based data is limited, while satellite observations can be obtained for any location on Earth, and collocate with any NSB photometric station. Our investigation also highlighted that SYNOP data are unreliable when cloud amount is low. This is due to the different fields of view for SQM (20°) and SYNOP (180°) observations of broken cloud. |
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0022-4073 |
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GFZ @ kyba @ |
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2580 |
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Author |
Wallner, S.; Kocifaj, M. |
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Title |
Impacts of surface albedo variations on the night sky brightness – A numerical and experimental analysis |
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Journal Article |
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Year |
2019 |
Publication |
Journal of Quantitative Spectroscopy and Radiative Transfer |
Abbreviated Journal |
Journal of Quantitative Spectroscopy and Radiative Transfer |
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239 |
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106648 |
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Skyglow; albedo; surface albedo; Sky Quality Meter; Austria; Europe |
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The aim of this paper is to analyze surface albedo impacts on artificial night sky brightness at zenith. The way in which these parameters correlate with each other is analyzed numerically and then experimentally by Sky Quality Meters (SQMs) in the city of Linz, Austria between 2016 and 2018. Three SQMs are located in city areas that differ in ground type, while other two are installed outside but near the city. To eliminate systematic errors of different SQMs or a missing inter-calibration of all devices, we examine relative change in zenithal brightness instead of its absolute values. However, the ground albedo not only depends on the ground type, but also shows seasonal variation most often driven by vegetation and environmental change. To understand these changes, we use SkyGlow simulator to perform numerical experiments on four different albedo models. The results have proven that seasonal variations are clearly visible as green city parts become darker around autumn and ratios to urban located SQMs increase. We show that there is a major difference in simulation results if either conducting city parts with various surface albedos or using only one averaged value over the whole city. The latter produces worse fit to the observed SQM data, implying that a use of various surface albedos is a need when modelling zenithal brightness in artificially lit areas of a city or town. Also, the seasonal changes of surface albedo cannot be neglected and the parameter itself must be included in the modelling tools. |
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Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria; stefan.wallner(at)univie.ac.at |
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Elsevier |
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English |
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0022-4073 |
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GFZ @ kyba @ |
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2675 |
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Kocifaj, M. |
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Title |
Ground albedo impacts on higher-order scattering spectral radiances of night sky |
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Journal Article |
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2019 |
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Journal of Quantitative Spectroscopy and Radiative Transfer |
Abbreviated Journal |
Journal of Quantitative Spectroscopy and Radiative Transfer |
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239 |
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106670 |
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skyglow |
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The contribution from ground reflected light to the night sky radiance is of increased interest because of constant modernization of street lighting systems that now efficiently eliminate light emissions above the horizontal plane, so the appreciable fraction of artificial light directed upwards is from ground reflection. Diffuse light of a night sky shows a positive correlation with ground albedo (α), but it seems there is no linear trend between α and the night sky brightness (NSB), at least not for all sky elements, and, the mechanism of this relationship becomes even more complicated due to multiple scattering effects. The extent to which the ground reflectance influences the higher-order scattering radiance of night sky, and, the factors that initiate the crossover from single- to multiple-scattering dominance of the sky glow has been virtually unexplored until now.
We demonstrate here that albedo-induced effects in NSB exhibit an angular dependence, with amplitudes enhanced towards shorter wavelengths. For low values of ground reflectance and at short distances from a light source, the second-scattering radiance is found to be only a few percent of the first-order scattering radiance. However, the ratio of a higher- to the first-order scattering radiance gradually increases near horizon, specifically at the side opposite to the azimuthal position of the light source. Also the NSB in blue band has decreasing gradation tendency when increasing the altitude above sea level. The findings in this paper are significant in a proper incorporation of higher-order scattering in modeling the NSB under elevated reflectance conditions, and may be critical for saving computational time. |
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0022-4073 |
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GFZ @ kyba @ |
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2679 |
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Bará, S.; Falchi, F.; Furgoni, R.; Lima, R.C. |
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Title |
Fast Fourier-transform calculation of artificial night sky brightness maps |
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Journal Article |
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2020 |
Publication |
Journal of Quantitative Spectroscopy and Radiative Transfer |
Abbreviated Journal |
Journal of Quantitative Spectroscopy and Radiative Transfer |
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240 |
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106658 |
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Skyglow; Light pollution; Atmospheric optics; Photometry; Radiometry; Fourier transforms |
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Light pollution poses a growing threat to optical astronomy, in addition to its detrimental impacts on the natural environment, the intangible heritage of humankind related to the contemplation of the starry sky and, potentially, on human health. The computation of maps showing the spatial distribution of several light pollution related functions (e.g. the anthropogenic zenithal night sky brightness, or the average brightness of the celestial hemisphere) is a key tool for light pollution monitoring and control, providing the scientific rationale for the adoption of informed decisions on public lighting and astronomical site preservation. The calculation of such maps from satellite radiance data for wide regions of the planet with sub-kilometric spatial resolution often implies a huge amount of basic pixel operations, requiring in many cases extremely large computation times. In this paper we show that, using adequate geographical projections, a wide set of light pollution map calculations can be reframed in terms of two-dimensional convolutions that can be easily evaluated using conventional fast Fourier-transform (FFT) algorithms, with typical computation times smaller than 10^-6 s per output pixel. |
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Departamento de Física Aplicada, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Galicia, Spain; salva.bara(at)usc.es |
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Elsevier |
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English |
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English |
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0022-4073 |
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IDA @ john @ |
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2782 |
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Bará, S.; Rigueiro, I.; Lima, R.C. |
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Title |
Monitoring transition: Expected night sky brightness trends in different photometric bands |
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Journal Article |
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Year |
2019 |
Publication |
Journal of Quantitative Spectroscopy and Radiative Transfer |
Abbreviated Journal |
Journal of Quantitative Spectroscopy and Radiative Transfer |
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239 |
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106644 |
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Skyglow; Remote Sensing; Instrumentation |
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Several light pollution indicators are commonly used to monitor the effects of the transition from outdoor lighting systems based on traditional gas-discharge lamps to solid-state light sources. In this work we analyze a subset of these indicators, including the artificial zenithal night sky brightness in the visual photopic and scotopic bands, the brightness in the specific photometric band of the widely used Sky Quality Meter (SQM), and the top-of-atmosphere radiance detected by the VIIRS-DNB radiometer onboard the satellite Suomi-NPP. Using a single-scattering approximation in a layered atmosphere we quantitatively show that, depending on the transition scenarios, these indicators may show different, even opposite behaviors. This is mainly due to the combined effects of the changes in the sources' spectra and angular radiation patterns, the wavelength-dependent atmospheric propagation processes and the differences in the detector spectral sensitivity bands. It is suggested that the possible presence of this differential behavior should be taken into account when evaluating light pollution indicator datasets for assessing the outcomes of public policy decisions regarding the upgrading of outdoor lighting systems. |
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0022-4073 |
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GFZ @ kyba @ |
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2810 |
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