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Aubé, M., & Kocifaj, M. (2012). Using two light-pollution models to investigate artificial sky radiances at Canary Islands observatories: Light-pollution models and artificial sky radiances. Monthly Notices of the Royal Astronomical Society, 422(1), 819–830.
Abstract: Astronomical observations are increasingly limited by light pollution, which is a product of the over-illumination of the night sky. To predict both the angular distribution of scattered light and the ground-reaching radiative fluxes, a set of models has been introduced in recent decades. Two distinct numerical tools, MSNsRAu and ILLUMINA, are compared in this paper, with the aim of identifying their strengths and weaknesses. The numerical experiment comprises the simulation of spectral radiances in the region of the Canary Islands. In particular, the light fields near the Roque de los Muchachos and Teide observatories are computed under various turbidity conditions. It is shown that ILLUMINA has enhanced accuracy at low elevation angles. However, ILLUMINA is time-consuming because of the two scattering orders incorporated into the calculation scheme. Under low-turbidity conditions and for zenith angles smaller than 70° the two models agree well, and thus can be successfully applied to typical cloudless situations at the majority of observatories. MSNsRAu is well optimized for large-scale simulations. In particular, the grid size is adapted dynamically depending on the distance between a light source and a hypothetical observer. This enables rapid numerical modelling for large territories. MSNsRAu is also well suited for the mass modelling of night-sky radiances after ground-based light sources are hypothetically changed. This enables an optimum design of public lighting systems and a time-efficient evaluation of the optical effects related to different lamp spectra or different lamp distributions. ILLUMINA provides two diagnostic geographical maps to help local authorities concerned about light-pollution control. The first map allows the identification of the relative contribution of each ground element to the observed sky radiance at a given viewing angle, while the second map gives the sensitivity, basically saying how each ground element contributes per lumen installed.
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Kocifaj, M., & Solano Lamphar, H. A. (2014). Skyglow: a retrieval of the approximate radiant intensity function of ground-based light sources. Monthly Notices of the Royal Astronomical Society, 439(4), 3405–3413.
Abstract: The angular distribution of the light emitted from a city is an important source of information about public lighting systems and it also plays a key role in modelling the skyglow. Usually, the upwardly directed radiation is characterized through a parametrized emission function â a semi-empirical approach as a reasonable approximation that allows for fast computations. However, theoretical or experimental retrievals of emission characteristics are extremely difficult to obtain because of both the complexity of radiative transfer methods and/or the lack of highly specialized measuring devices.
Our research has been conducted with the specific objective to identify an efficient theoretical technique for retrieval of the emission pattern of ground-based light sources in order to determine the optimum values of the scaling parameters of the Garstang function. In particular, the input data involve the zenith luminance or radiance with horizontal illuminance or irradiance. Theoretical ratios of zenith luminance LV(0) to horizontal illuminance DV are calculated for a set of distances d that separate a hypothetical observer from the light source (a city or town). This approach is advantageous because inexpensive traditional equipment can be used to obtain the mean values of the Garstang parameters. Furthermore, it can also be applied to other parametrizable emission functions and to any measuring site, even one with a masked horizon. |
Kocifaj, M., Solano Lamphar, H. A., & Kundracik, F. (2015). Retrieval of Garstang's emission function from all-sky camera images. Mon. Not. R. Astron. Soc., 453(1), 819–827.
Abstract: The emission function from ground-based light sources predetermines the skyglow features to a large extent, while most mathematical models that are used to predict the night sky brightness require the information on this function. The radiant intensity distribution on a clear sky is experimentally determined as a function of zenith angle using the theoretical approach published only recently in MNRAS, 439, 3405â3413. We have made the experiments in two localities in Slovakia and Mexico by means of two digital single lens reflex professional cameras operating with different lenses that limit the system's field-of-view to either 180º or 167º. The purpose of using two cameras was to identify variances between two different apertures. Images are taken at different distances from an artificial light source (a city) with intention to determine the ratio of zenith radiance relative to horizontal irradiance. Subsequently, the information on the fraction of the light radiated directly into the upward hemisphere (F) is extracted. The results show that inexpensive devices can properly identify the upward emissions with adequate reliability as long as the clear sky radiance distribution is dominated by a largest ground-based light source. Highly unstable turbidity conditions can also make the parameter F difficult to find or even impossible to retrieve. The measurements at low elevation angles should be avoided due to a potentially parasitic effect of direct light emissions from luminaires surrounding the measuring site.
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Müller, A., Wuchterl, G., & Sarazin, M. (2011). Measuring the Night Sky Brightness with the Lightmeter. ReVMexAA, 41, 46â49.
Abstract: We present a newly developed, low-cost photometer for long-term monitoring of the night sky brightness and
light pollution on Earth. The so-called Lightmeter is an as far as possible stand-alone operational, fully weatherproof, and maintenance-free device. It provides a high data sampling rate of up to 1 Hz as well as a superb sensitivity covering the whole brightness range down to the darkest night time conditions. The excellent performance of the Lightmeter allows a continuously monitoring of the night sky brightness and opens a wide range of applications at an observatory site like determining overall sky conditions in real time, cloud detection and estimation of their velocity, measuring relative changes in extinction as well as the detection of long term trends in brightness caused by an increase of artificial illumination. We will present first results of measurements taken at Cerro Armazones, one of the best obser |