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Author  |
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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Year |
2020 |
Publication |
Journal of Quantitative Spectroscopy and Radiative Transfer |
Abbreviated Journal |
Journal of Quantitative Spectroscopy and Radiative Transfer |
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Volume |
240 |
Issue |
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Pages |
106658 |
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Keywords |
Skyglow; Light pollution; Atmospheric optics; Photometry; Radiometry; Fourier transforms |
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Abstract |
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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Address |
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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Call Number |
IDA @ john @ |
Serial |
2782 |
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Author |
Bará, S.; Lima, R.C.; Zamorano, J. |
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Title |
Monitoring Long-Term Trends in the Anthropogenic Night Sky Brightness |
Type |
Journal Article |
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Year |
2019 |
Publication |
Sustainability |
Abbreviated Journal |
Sustainability |
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Volume |
11 |
Issue |
11 |
Pages |
3070 |
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Keywords |
Skyglow |
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Abstract |
Monitoring long-term trends in the evolution of the anthropogenic night sky brightness is a demanding task due to the high dynamic range of the artificial and natural light emissions and the high variability of the atmospheric conditions that determine the amount of light scattered in the direction of the observer. In this paper, we analyze the use of a statistical indicator, the mFWHM, to assess the night sky brightness changes over periods of time larger than one year. The mFWHM is formally defined as the average value of the recorded magnitudes contained within the full width at half-maximum region of the histogram peak corresponding to the scattering of artificial light under clear skies in the conditions of a moonless astronomical night (sun below −18°, and moon below −5°). We apply this indicator to the measurements acquired by the 14 SQM detectors of the Galician Night Sky Brightness Monitoring Network during the period 2015–2018. Overall, the available data suggest that the zenithal readings in the Sky Quality Meter (SQM) device-specific photometric band tended to increase during this period of time at an average rate of +0.09 magSQM/arcsec2 per year. |
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ISSN |
2071-1050 |
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Call Number |
GFZ @ kyba @ |
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2552 |
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Author |
Bará, S.; Nievas, M.; Sanchez de Miguel, A.; Zamorano, J. |
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Title |
Zernike analysis of all-sky night brightness maps |
Type |
Journal Article |
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Year |
2014 |
Publication |
Applied Optics |
Abbreviated Journal |
Appl Opt |
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Volume |
53 |
Issue |
12 |
Pages |
2677-2686 |
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Keywords |
modeling; light at night; light pollution; all-sky; Zernike polynomials; image decomposition; sky brightness |
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Abstract |
All-sky night brightness maps (calibrated images of the night sky with hemispherical field-of-view (FOV) taken at standard photometric bands) provide useful data to assess the light pollution levels at any ground site. We show that these maps can be efficiently described and analyzed using Zernike circle polynomials. The relevant image information can be compressed into a low-dimensional coefficients vector, giving an analytical expression for the sky brightness and alleviating the effects of noise. Moreover, the Zernike expansions allow us to quantify in a straightforward way the average and zenithal sky brightness and its variation across the FOV, providing a convenient framework to study the time course of these magnitudes. We apply this framework to analyze the results of a one-year campaign of night sky brightness measurements made at the UCM observatory in Madrid. |
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Address |
Ãrea de Óptica, Dept. de FÃsica Aplicada, Fac. de FÃsica, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Galicia, Spain |
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Optical Society of America |
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English |
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0003-6935 |
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Notes |
PMID:24787595 |
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Call Number |
IDA @ john @ |
Serial |
318 |
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Author |
Bará, S.; Ribas, S.; Kocifaj, M. |
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Title |
Modal evaluation of the anthropogenic night sky brightness at arbitrary distances from a light source |
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Journal Article |
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Year |
2015 |
Publication |
Journal of Optics |
Abbreviated Journal |
J. of Optics |
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Volume |
17 |
Issue |
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Pages |
105607 |
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Keywords |
Skyglow; light propagation, atmospheric optics, light pollution |
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Abstract |
The artificial emissions of light contribute to a high extent to the observed brightness of the night sky in many places of the world. Determining the all-sky radiance of anthropogenic origin requires solving the radiative transfer equation for ground-level light sources, generally resorting to a double-scattering approximation in order to account for the observed radiance patterns with a reasonable degree of accuracy. Since the all-sky radiance distribution produced by an elementary light source depends on the distance to the observer in a way that is not immediately obvious, the contributions of sources located at different distances have to be computed on an individual basis, solving for each one the corresponding scattering integrals. In this paper we show that these calculations may be significantly alleviated by using a modal approach, whereby the hemispheric night-sky radiance is expanded in terms of a convenient basis of two-dimensional (2D) orthogonal functions. Since the modal coefficients of this expansion do vary smoothly with the distance to the observer, the all-sky brightness distributions produced by light sources located at arbitrary intermediate distances can be efficiently estimated by interpolation, provided that the coefficients at a discrete set of distances are accurately determined beforehand. |
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Area de Optica, Universidade de Santiago de Compostela Campus Sur, E-15782, Santiago de Compostela, Spain; salva.bara(at)usc.es |
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IOP |
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English |
Summary Language |
English |
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ISSN |
2040-8986 |
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no |
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Call Number |
IDA @ john @ |
Serial |
1235 |
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Author |
Bará, S.; Rigueiro, I.; Lima, R.C. |
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Title |
Monitoring transition: Expected night sky brightness trends in different photometric bands |
Type |
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 |
239 |
Issue |
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Pages |
106644 |
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Keywords |
Skyglow; Remote Sensing; Instrumentation |
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Abstract |
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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Call Number |
GFZ @ kyba @ |
Serial |
2810 |
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