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- Spectral measurement of an arquiled arquicity R1 LED streetlight installed at Cumeada, dark sky AlquevaPublication . Lima, Raul Cerveira; Bará, SalvadorDuring late 2016 the national Portuguese electricity operator, Electricidade de Portugal (EDP), changed the streetlights of the hamlet of Cumeada, Reguengos de Monsaraz, Évora, to white light emission diodes technology (LED). The hamlet of Cumeada is within the borders of the Starlight Tourism Destination Dark Sky Alqueva (DSA). We evaluated in lab the spectrum and the CCT of one of those LED. The results revealed the LED luminaires installed in the hamlet are not appropriate for use in a dark skies reserve.
- Testing a cloudless model of light pollution propagation on two dark sky regions in PortugalPublication . Lima, Raul CerveiraLight pollution (LP) affects Mainland Portugal in accordance to its asymmetric demographic distribution. The strongest LP sources are distributed along the densely populated coastal line, whereas the interior north and south of the country is still generally well preserved due to a much lower demographic density. In the period 2010-2014, on selected moonless and cloudless nights, we assessed the skyglow of two dark sky regions (the Peneda-Gerês National Park, a mountain region, and the Lake Alqueva region, typically plain) with a portable Unihedron SQM-L unit pointed handheld to the zenith. The data from the field measurements was used to compare to one light pollution propagation model (Kocifaj, 2007), using calibrated VIIRS DNB satellite upwards radiance (calibration by Zamorano et al, 2012) as input to the model. The results obtained from the model are favourably compared to the field measurements. We proceeded to a set of tests with the model (programmed in MATLAB) to find the best fit. Our best results were achieved by analysing the data by night rather than the global set of data. Our results were used to apply to the classification of the Alqueva as a Starlight Tourism Destination and light pollution guidelines were implemented in the Peneda-Gerês Park’s Management Plan.
- Light pollution: Assessment of sky glow on two dark sky regions of PortugalPublication . Lima, Raul Cerveira; Pinto da Cunha, José; Peixinho, NunoArtificial light at night (ALAN), producing light pollution (LP), is not a matter restricted to astronomy anymore. Light is part of modern societies and, as a consequence, the natural cycle day-night (bright-dark) has been interrupted in a large segment of the global population. There is increasing evidence that exposure to certain types of light at night and beyond threshold levels may produce hazardous effects to humans and the environment. The concept of "dark skies reserves" is a step forward in order to preserve the night sky and a means of enhancing public awareness of the problem of spread of light pollution worldwide. The aim of this study was to assess the skyglow at two sites in Portugal, the Peneda-Gerês National Park (PNPG) and the region now known as Dark Sky Alqueva Reserve. The latter site was classified as a "Starlight Tourism Destination" by the Starlight Foundation (the first in the world to achieve this classification) following a series of night sky measurements in situ described herein. The measurements at PNPG also contributed to the new set of regulations concerning light pollution at this national park. This study presents the first in situ systematic measurements of night sky brightness, showing that at the two sites the skies are mostly in levels 3 to 4 of the Bortle 9-level scale (with level 1 being the best achievable). The results indicate that the sources of light pollution and skyglow can be attributed predominantly to contamination from nearby urban regions.
- Quantitative evaluation of outdoor artificial light emissions using low Earth orbit radiometersPublication . Bará, Salvador; Bao-Varela, Carmen; Lima, Raul CerveiraLow Earth orbit radiometers allow monitoring nighttime anthropogenic light emissions in wide areas of the planet. In this work we describe a simple model for assessing significant outdoor lighting changes at the municipality level using on-orbit measurements complemented with ground-truth information. We apply it to evaluate the transformation effected in the municipality of Ribeira (42°33'23"N, 8°59' 32" W) in Galicia, which in 2015 reduced the amount of installed lumen in its publicly-owned outdoor lighting system from 93.2 to 28.7 Mlm. This significant cutback, with the help of additional controls, allowed to reduce from 0.768 to 0.208 Mlm/km2 the lumen emission density averaged across the territory. In combination with the VIIRS-DNB annual composite readings these data allow to estimate that the relative weight of the emissions of the public treetlight system with respect to the total emissions of light in the municipality changed from an initial value of 74.86% to 44.68% after the transformation. The effects of the sources’ spectral shift and the photon calibration factor on the radiance reported by the VIIRS-DNB are also evaluated.
- Fast Fourier-transform calculation of artificial night sky brightness mapsPublication . Bará, Salvador; Falchi, Fabio; Furgoni, Riccardo; Lima, Raul CerveiraLight 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.
- Monitoring transition: expected night sky brightness trends in different photometric bandsPublication . Bará, Salvador; Rigueiro, Iago; Lima, Raul CerveiraSeveral 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.
- Estimating the relative contribution of streetlights, vehicles, and residential lighting to the urban night sky brightnessPublication . Bará, Salvador; Rodríguez-Arós, Ángel; Pérez, Marcos; Tosar, Borja; Lima, Raul Cerveira; Sánchez de Miguel, Alejandro; Zamorano, JaimeUnder stable atmospheric conditions the brightness of the urban sky varies throughout the night following the time course of the anthropogenic emissions of light. Different types of artificial light sources (e.g. streetlights, residential, and vehicle lights) have specific time signatures, and this feature makes it possible to estimate the amount of brightness contributed by each of them. Our approach is based on transforming the time representation of the zenithal night sky brightness into a modal expansion in terms of the time signatures of the different sources of light. The modal coefficients, and hence the absolute and relative contributions of each type of source, can be estimated by means of a linear least squares fit. A practical method for determining the time signatures of different contributing sources is also described, based on wide-field time-lapse photometry of the urban nightscape. Our preliminary results suggest that, besides the dominant streetlight contribution, artificial light leaking out of the windows of residential buildings may account for a significant share of the time-varying part of the zenithal night sky brightness at the measurement locations, whilst the contribution of the vehicle lights seems to be significantly smaller.
- Monitoring long-term trends in the anthropogenic night sky brightnessPublication . Bará, Salvador; Lima, Raul Cerveira; Zamorano, JaimeMonitoring 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.
- A rising risk to human health: assessment of light pollution on two dark sky regions of PortugalPublication . Lima, Raul Cerveira; Cunha, José Pinto da; Peixinho, NunoBad public and private artificial light planning is the main cause for light pollution (LP). Night illumination is part of modern societies, reaching increasing levels with consequences on various fields that only recently began to be studied. Residents of large cities are almost totally deprived from a starry night. UNESCO, UNTWO and IAU’s Declaration in Defence of the Night Sky and the Right to Starlight state that “an unpolluted night sky that allows the enjoyment and contemplation of the firmament should be considered an inalienable right equivalent to all other socio-cultural and environmental rights. Hence the progressive degradation of the night sky must be regarded as a fundamental loss” and that “the intelligent use of artificial lighting that minimizes sky glow and avoids obtrusive visual impact on both humans and wildlife should be promoted. This strategy would involve a more efficient use of energy so as to meet the wider commitments made on climate change, and for the protection of the environment”(Marín & Jafari, 2007).The observation and study of the night sky both at professional and casual or amateur levels is the first to be affected by light pollution thus being the primary reason to study LP until recently. However, other LP effects are already known to affect the human being such as modifications of the circadian rhythm(Stevens, 2006). More recent studies suggest LP as a risk factor for human breast and prostate cancer(Haim & Portnov, 2013). Other direct and indirect effects on the environment include natural resources consumption and effects on biodiversity, namely nocturnal fauna(Rich & Longcore, 2005).The creation of dark-skies protected areas is one form to preserve the night sky of some regions that still have a good dark sky quality. It is also a way to draw the attention of public and stakeholders to this growing problem. More than a local effect caused mainly by large urban centres, light pollution propagates to regions that are tensor more kilometres away from those populated regions, affecting places once with good night sky quality even a few years ago. Two examples of regions in Portugal that offer good dark skies are, at the north of the country, the Peneda-Gerês National Park and, at the south, the Alentejo’s region of Alqueva, both commonly known to have good dark skies but that have not been previously measured. The latter got its classification as «dark sky reserve» based on the values of night sky brightness obtained for this work.
- Poluição luminosaPublication . International Astronomical Union; Lima, Raul Cerveira