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Zamorano, J.; Sánchez de Miguel, A.; Ocaña, F.; Pila-Diez, B.; Gómez Castaño, J.; Pascual, S.; Tapia, C.; Gallego, J.; Fernandez, A.; Nievas, M. |
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Title |
Testing sky brightness models against radial dependency: a dense two dimensional survey around the city of Madrid, Spain |
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Year |
2016 |
Publication |
Journal of Quantitative Spectroscopy and Radiative Transfer |
Abbreviated Journal |
JQSRT |
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181 |
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52-66 |
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Skyglow; measurements; light pollution; artificial light at night; modeling; Madrid; Spain |
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We present a study of the night sky brightness around the extended metropolitan area of Madrid using Sky Quality Meter (SQM) photometers. The map is the first to cover the spatial distribution of the sky brightness in the center of the Iberian peninsula. These surveys are neccessary to test the light pollution models that predict night sky brightness as a function of the location and brightness of the sources of light pollution and the scattering of light in the atmosphere. We describe the data-retrieval methodology, which includes an automated procedure to measure from a moving vehicle in order to speed up the data collection, providing a denser and wider survey than previous works with similar time frames. We compare the night sky brightness map to the nocturnal radiance measured from space by the DMSP satellite. We find that i) a single source model is not enough to explain the radial evolution of the night sky brightness, despite the predominance of Madrid in size and population, and ii) that the orography of the region should be taken into account when deriving geo-specific models from general first-principles models. We show the tight relationship between these two luminance measures. This finding sets up an alternative roadmap to extended studies over the globe that will not require the local deployment of photometers or trained personnel. |
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Dept. Astrof´ısica y CC. de la Atm´osfera, Universidad Complutense de Madrid, Ciudad Universitaria, 28040 Madrid, Spain |
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IDA @ john @ |
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1323 |
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Kocifaj, M.; Kómar, L. |
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Title |
A role of aerosol particles in forming urban skyglow and skyglow from distant cities |
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Journal Article |
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Year |
2016 |
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Monthly Notices of the Royal Astronomical Society |
Abbreviated Journal |
MNRAS |
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458 |
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1 |
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438-448 |
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Keywords |
Skyglow; scattering; atmospheric effects; artificial light; numerical modeling; GIS-based modeling; light pollution |
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Abstract |
Aerosol particles may represent the largest uncertainty about skyglow change in many locations under clear sky conditions. This is because aerosols are ubiquitous in the atmosphere and influence the ground-reaching radiation in different ways depending on their concentrations, origins, shapes, sizes, and compositions. Large particles tend to scatter in Fraunhofer diffraction regime, while small particles can be treated in terms of Rayleigh formalism. However, the role of particle microphysics in forming the skyglow still remains poorly quantified. We have shown in this paper that the chemistry is somehow important for backscattering from large particles that otherwise work as efficient attenuators of light pollution if composed of absorbing materials. The contribution of large particles to the urban skyglow diminishes as they become more spherical in shape. The intensity of backscattering from non-absorbing particles is more-or-less linearly decreasing function of particle radius even if number size distribution is inversely proportional to the fourth power of particle radius. This is due to single particle backscattering that generally increases steeply as the particle radius approaches large values. Forward scattering depends on the particle shape but is independent of the material composition, thus allowing for a simplistic analytical model of skyglow from distant cities. The model we have developed is based on mean value theorem for integrals and incorporates the parametrizable Garstang's emission pattern, intensity decay along optical beam path, and near-forward scattering in an atmospheric environment. Such model can be used by modellers and experimentalists for rapid estimation of skyglow from distant light sources. |
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ICA, Slovak Academy of Sciences, Dúbravská Road 9, 845 03 Bratislava, Slovak Republic; kocifaj(at)savba.sk |
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Oxford Journals |
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English |
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IDA @ john @ |
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1361 |
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Kocifaj, M. |
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Title |
Light-pollution model for cloudy and cloudless night skies with ground-based light sources |
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2007 |
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Applied Optics |
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Appl. Opt. |
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46 |
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15 |
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3013 |
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light pollution; modeling |
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The scalable theoretical model of light pollution for ground sources is presented. The model is successfully employed for simulation of angular behavior of the spectral and integral sky radiance and∕or luminance during nighttime. There is no restriction on the number of ground-based light sources or on the spatial distribution of these sources in the vicinity of the measuring point (i.e., both distances and azimuth angles of the light sources are configurable). The model is applicable for real finite-dimensional surface sources with defined spectral and angular radiating properties contrary to frequently used point-source approximations. The influence of the atmosphere on the transmitted radiation is formulated in terms of aerosol and molecular optical properties. Altitude and spectral reflectance of a cloud layer are the main factors introduced for simulation of cloudy and∕or overcast conditions. The derived equations are translated into numerically fast code, and it is possible to repeat the entire set of calculations in real time. The parametric character of the model enables its efficient usage by illuminating engineers and∕or astronomers in the study of various light-pollution situations. Some examples of numerical runs in the form of graphical results are presented. |
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0003-6935 |
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IDA @ john @ |
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277 |
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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 |
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Journal Article |
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2014 |
Publication |
Applied Optics |
Abbreviated Journal |
Appl Opt |
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53 |
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12 |
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2677-2686 |
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modeling; light at night; light pollution; all-sky; Zernike polynomials; image decomposition; sky brightness |
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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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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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PMID:24787595 |
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IDA @ john @ |
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318 |
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Noll, S.; Kausch, W.; Barden, M.; Jones, A.M.; Szyszka, C.; Kimeswenger, S.; Vinther, J. |
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Title |
An atmospheric radiation model for Cerro Paranal: I. The optical spectral range* |
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Journal Article |
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2012 |
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Astronomy & Astrophysics |
Abbreviated Journal |
A&A |
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543 |
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A92 |
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atmospheric effects; site testing; radiative transfer; radiation mechanisms: general; scattering; techniques; spectroscopic; modeling; observatories; Cerro Paranal |
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Aims. The Earth’s atmosphere affects ground-based astronomical observations. Scattering, absorption, and radiation processes deteriorate the signal-to-noise ratio of the data received. For scheduling astronomical observations it is, therefore, important to accurately estimate the wavelength-dependent effect of the Earth’s atmosphere on the observed flux.
Methods. In order to increase the accuracy of the exposure time calculator of the European Southern Observatory’s (ESO) Very Large Telescope (VLT) at Cerro Paranal, an atmospheric model was developed as part of the Austrian ESO In-Kind contribution. It includes all relevant components, such as scattered moonlight, scattered starlight, zodiacal light, atmospheric thermal radiation and absorption, and non-thermal airglow emission. This paper focuses on atmospheric scattering processes that mostly affect the blue (<0.55 μm) wavelength regime, and airglow emission lines and continuum that dominate the red (>0.55 μm) wavelength regime. While the former is mainly investigated by means of radiative transfer models, the intensity and variability of the latter is studied with a sample of 1186 VLT FORS 1 spectra.
Results. For a set of parameters such as the object altitude angle, Moon-object angular distance, ecliptic latitude, bimonthly period, and solar radio flux, our model predicts atmospheric radiation and transmission at a requested resolution. A comparison of our model with the FORS 1 spectra and photometric data for the night-sky brightness from the literature, suggest a model accuracy of about 20%. This is a significant improvement with respect to existing predictive atmospheric models for astronomical exposure time calculators. |
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0004-6361 |
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IDA @ john @ |
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274 |
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