Article

Photometric indicators of visual night sky quality derived from all-sky brightness maps

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Abstract

Wide angle or fisheye cameras provide a high resolution record of artificial sky glow, which results from the scattering of escaped anthropogenic light by the atmosphere, over the sky vault in the moonless nocturnal environment. Analysis of this record yields important indicators of the extent and severity of light pollution. The following indicators were derived through numerical analysis of all-sky brightness maps: zenithal, average all-sky, median, brightest, and darkest sky brightness. In addition, horizontal and vertical illuminance resulting from sky brightness were computed. A natural reference condition to which the anthropogenic component may be compared is proposed for each indicator, based upon an iterative analysis of a high resolution natural sky model. All-sky brightness data, calibrated in the V band by photometry of standard stars and converted to luminance, from 406 separate data sets were included in an exploratory analysis. Of these, six locations representing a wide range of severity of impact from artificial sky brightness were selected as examples and examined in detail. All-sky average brightness is the most unbiased indicator of impact to the environment, and is more sensitive and accurate in areas of slight to moderate light pollution impact than zenith brightness. Maximum vertical illuminance provides an excellent indicator of impacts to wilderness character, as does measures of the brightest portions of the sky. Zenith brightness, the workhorse of field campaigns, is compared to the other indicators and found to correlate well with horizontal illuminance, especially at relatively bright sites. The median sky brightness describes a brightness threshold for the upper half of the sky, of importance to telescopic optical astronomy. Numeric indicators, in concert with all-sky brightness maps, provide a complete assessment of visual sky quality at a site.

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... However, with both approaches only the luminance (or radiance) at zenith is measured. The zenith luminance is not a good proxy for the total light available at a site, and it is not straightforward to convert it to horizontal or scalar illuminance, commonly used by biologists, as the night sky brightness is usually non-uniform [35,36]. Commercial luxmeters have the drawback that they are either not sensitive enough or, when calibrated for low light levels, are relatively expensive. ...
... Information of the spatial distribution of the night sky brightness is relevant for ELP studies and can be obtained from imaging sensors as nicely outlined by Duriscoe [35]. Several approaches to measure light pollution with imaging sensors exist, like the all-sky transmission monitor (ASTMON) [38,39], CCD cameras with sophisticated mechanics to built all-sky mosaics like the US National Park Camera [40] as well as other custom built camera systems [41]. ...
... The importance of imaging devices for light pollution measurements has been pointed out earlier [35,42,43]. However, it is not widely recognized in the community investigating ELP, with the exception of work on marine turtle hatchlings [44]. ...
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Article
Artificial skyglow is constantly growing on a global scale, with potential ecological consequences ranging up to affecting biodiversity. To understand these consequences, worldwide mapping of skyglow for all weather conditions is urgently required. In particular, the amplification of skyglow by clouds needs to be studied, as clouds can extend the reach of skyglow into remote areas not affected by light pollution on clear nights. Here we use commercial digital single lens reflex cameras with fisheye lenses for all-sky photometry. We track the reach of skyglow from a peri-urban into a remote area on a clear and a partly cloudy night by performing transects from the Spanish town of Balaguer towards Montsec Astronomical Park. From one single all-sky image, we extract zenith luminance, horizontal and scalar illuminance. While zenith luminance reaches near-natural levels at 5km distance from the town on the clear night, similar levels are only reached at 27km on the partly cloudy night. Our results show the dramatic increase of the reach of skyglow even for moderate cloud coverage at this site. The powerful and easy-to-use method promises to be widely applicable for studies of ecological light pollution on a global scale also by non-specialists in photometry.
... A similar method has been used to improve zenith brightness measures with the SQM-L [7] . Values of 171 μcd m −2 and 250 μcd m −2 have been proposed as the reference conditions for ZL and ASL, respectively, in the absence of artificial sky glow [8] . These values provide a baseline level for expressing the scale of sky glow. ...
... The ratio indicators utilized in this paper are termed all-sky average light pollution ratio (ALR) and zenith light pollution ratio (ZLR). Numeric indicators of artificial sky brightness were discussed in detail by Duriscoe [8] , including their derivation from all sky photometric measurements and application to night sky quality assessments. ...
... The modeling experiment described in Section 2.4 and summarized in Section 3 predicts that the ALR is always higher than the ZLR, by a factor of 1.58-3.27. Sky brightness measurements have shown that ALR/ZLR is highest in the darkest locations, and that the range is 2.0-6.0 (see Table 1 and [8] ). Thus the ALR is a more sensitive indicator in darker locations, and has greater applicability to an assessment of visual quality in protected areas. ...
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Article
We present a simplified method using geographic analysis tools to predict the average artificial luminance over the hemisphere of the night sky, expressed as a ratio to the natural condition. The VIIRS Day/Night Band upward radiance data from the Suomi NPP orbiting satellite was used for input to the model. The method is based upon a relation between sky glow brightness and the distance from the observer to the source of upward radiance. This relationship was developed using a Garstang radiative transfer model with Day/Night Band data as input, then refined and calibrated with ground-based all-sky V-band photometric data taken under cloudless and low atmospheric aerosol conditions. An excellent correlation was found between observed sky quality and the predicted values from the remotely sensed data. Thematic maps of large regions of the earth showing predicted artificial V-band sky brightness may be quickly generated with modest computing resources. We have found a fast and accurate method based on previous work to model all-sky quality. We provide limitations to this method. The proposed model meets requirements needed by decision makers and land managers of an easy to interpret and understand metric of sky quality.
... However, this is not valid for most scenarios, as usually the NSB is not uniform [16,21,28,39]. Therefore, the horizontal illuminance can only be roughly approximated from narrow angle zenith measurements alone [27,39]. ...
... However, this is not valid for most scenarios, as usually the NSB is not uniform [16,21,28,39]. Therefore, the horizontal illuminance can only be roughly approximated from narrow angle zenith measurements alone [27,39]. From all-sky brightness maps, the horizontal illuminance (incident at the imaging plane of the camera) can be obtained when incorporating a cosine correction [39]. ...
... Therefore, the horizontal illuminance can only be roughly approximated from narrow angle zenith measurements alone [27,39]. From all-sky brightness maps, the horizontal illuminance (incident at the imaging plane of the camera) can be obtained when incorporating a cosine correction [39]. The cosine corrected angular luminance distribution is shown in Fig. 6 a) in NSU. ...
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Article
Near all-sky imaging photometry was performed from a boat on the Gulf of Aqaba to measure the night sky brightness in a coastal environment. The boat was not anchored, and therefore drifted and rocked. The camera was mounted on a tripod without any inertia/motion stabilization. A commercial digital single lens reflex (DSLR) camera and fisheye lens were used with ISO setting of 6400, with the exposure time varied between 0.5 s and 5 s. We find that despite movement of the vessel the measurements produce quantitatively comparable results apart from saturation effects. We discuss the potential and limitations of this method for mapping light pollution in marine and freshwater systems. This work represents the proof of concept that all-sky photometry with a commercial DSLR camera is a viable tool to determine light pollution in an ecological context from a moving boat.
... Indicators of sky quality derived from artificial all sky luminance maps are described by Duriscoe (2016). Here we focus on the use of the average of all observations throughout the sky, rank statistics performed on the luminance values, particularly the median or 50th percentile, and the ''brightest square degree'' or the 99.995th percentile, and the use of horizontal and maximum vertical illuminance is described. ...
... Bright light domes from distant cities may produce a strong vertical illuminance in an otherwise relatively dark location. The natural reference condition for these indicators is predicted at 0.8 mlux for horizontal, 0.4 mlux for vertical (Duriscoe 2016). All of the indicators may be expressed as a ratio to natural conditions, or ''percent above natural.'' ...
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Article
Human activity is rapidly increasing the negative impact of artificial skyglow at even the most remote professional observatory sites. Assessment of the actual impact requires an understanding of the propagation as a function of source spectral energy distribution. The higher blue content of light-emitting diodes being widely used as replacement for sodium discharge lamps has greater impact closer to the source, and less impact for more distant mountain-top sites. All-sky cameras with moderate angular resolution provide data and metrics sufficient to model and remove celestial contributions and provide measures of artificial light contribution. The natural skyglow is significantly affected by solar activity, which must be accounted for in determining secular trends in the artificial component. With the availability of the New World Atlas of the Artificial Sky Brightness, a direct comparison is made of the modeled artificial contribution to the sites with the largest aperture telescopes, noting the possible systematic errors in individual cases. Population growth of the nearest urban centers allows a prediction of the change in that brightness over a decade. All site protections are effected primarily by national or regional regulation. A collection of worldwide regulations shows that most are leveraged off environmental protection statutes, while in the U.S., they are largely based on land-use zones. Particular examples are presented in more detail for Flagstaff, Arizona, and the Island of Hawai’i. The latest rapidly growing threat is that of reflected sunlight from large constellations of satellites in low-earth orbit. A snapshot is provided of that rapidly changing situation. In all cases, astronomers must become very proactive in educating the public about the cultural value of visual or naked eye astronomy as well as the science and the need for access to a dark night sky for astronomical research.
... The use of these well-known metrics is intended to facilitate a first discussion of the issue of the restoration of urban skies. More comprehensive metrics, including all-sky and near-horizon average brightnesses [48][49][50] should be taken into account in future works for a full formulation of the desired features of the urban nightscapes. ...
... A similar definition can be applied to any sky quality indicator linearly dependent on the spectral radiance at the observer location, including, but not limited to, the zenith radiance, the average hemispheric radiance, the horizontal illuminance, or the average radiance within some angular strip above the horizon [46][47][48]. The formulation developed below applies equally to any of these indicators, and hence may be understood as representing any of them; for the particular purpose of this paper, however, we will identify with the zenith sky brightness. ...
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Could we enjoy starry skies in our cities again? Arguably yes. The actual number of visible stars will depend, among other factors, on the spatial density of the overall city light emissions. In this paper it is shown that reasonably dark skies could be achieved in urban settings, even at the center of large metropolitan areas, if the light emissions are kept within admissible levels and direct glare from the light sources is avoided. These results may support the adoption of science-informed, democratic public decisions on the use of light in our municipalities, with the goal of recovering the possibility of contemplating the night sky everywhere in our planet.
... The use of these well-known metrics is intended to facilitate a first discussion of the issue of the restoration of urban skies. More comprehensive metrics, including all-sky and near-horizon average brightnesses [48][49][50] should be taken into account in future works for a full formulation of the desired features of the urban nightscapes. ...
... A similar definition can be applied to any sky quality indicator linearly dependent on the spectral radiance at the observer location, including, but not limited to, the zenith radiance, the average hemispheric radiance, the horizontal illuminance, or the average radiance within some angular strip above the horizon [46][47][48]. The formulation developed below applies equally to any of these indicators, and hence may be understood as representing any of them; for the particular purpose of this paper, however, we will identify with the zenith sky brightness. ...
Preprint
Could we enjoy starry skies in our cities again? Arguably yes. The actual number of visible stars will depend, among other factors, on the spatial density of the overall city light emissions. In this paper it is shown that reasonably dark skies could be achieved in urban settings, even at the center of large metropolitan areas, if the light emissions are kept within admissible levels and direct glare from the light sources is avoided. These results may support the adoption of science-informed, democratic public decisions on the use of light in our municipalities, with the goal of recovering the possibility of contemplating the night sky everywhere in our planet.
... Increasingly, researchers recognize the value of detecting the brightness over the entire 2π steradians of sky through the use of calibrated, two-dimensional imaging techniques. A 2D imaging method allows for the extraction of a number of useful vector and scalar metrics from all-sky maps not possible with other methods [105]. 2D models of natural sources of light in the night sky can be subtracted from all-sky imagery, enabling the clear identification of distinctly anthropogenic sources [106]. ...
... The mean night sky brightness, averaged over the entire sky, is the most relevant parameter describing the impact of anthropogenic light at night on the nocturnal environment and yields a more reliable result than zenith luminance measurements alone, especially in places with low to moderate amounts of light pollution [105]. Such measurements are not easily obtained in the field with single-channel devices, much less those intended to operate autonomously. ...
Full-text available
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Since the introduction of electric lighting over a century ago, and particularly in the decades following the Second World War, indications of artificial light on the nighttime Earth as seen from Earth orbit have increased at a rate exceeding that of world population growth during the same period. Modification of the natural photic environment at night is a clear and imminent consequence of the proliferation of anthropogenic light at night into outdoor spaces, and with this unprecedented change comes a host of known and suspected ecological consequences. In the past two decades, the conservation community has gradually come to view light pollution as a threat requiring the development of best management practices. Establishing those practices demands a means of quantifying the problem, identifying polluting sources, and monitoring the evolution of their impacts through time. The proliferation of solid-state lighting and the changes to source spectral power distribution it has brought relative to legacy lighting technologies add the complication of color to the overall situation. In this paper, I describe the challenge of quantifying light pollution threats to ecologically-sensitive sites in the context of efforts to conserve natural nighttime darkness, assess the current state of the art in detection and imaging technology as applied to this realm, review some recent innovations, and consider future prospects for imaging approaches to provide substantial support for darkness conservation initiatives around the world.
... However, despite the amount of experimental work on ALAN and ELP, the understanding of the nocturnal light field (natural and artificial) at a specific site under specific environmental conditions (e.g., clouds, snow) is still limited. The natural nocturnal light field changes due to the movement of celestial objects, including daily variation in daylength and moon illumination as well as a seasonal variation in the position of stars [23]. Weather conditions further impose changes on shorter timescales to the natural light field, because atmospheric conditions significantly alter the amount of light incident at the Earth's surface, and the surface reflectance can change due to changes in vegetation, soil moisture, or snow cover. ...
... Unfortunately, at the moment no measurement device or method that can provide all these parameters simultaneously at high resolution is available for dim light conditions. However, in the context of astronomical light pollution, all-sky cameras have emerged recently as a promising tool for night sky brightness measurements [23][24][25][26][27][28] (see discussion for more details). ...
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Article
Artificial light at night is a novel anthropogenic stressor. The resulting ecological light pollution affects a wide breadth of biological systems on many spatio-temporal scales, from individual organisms to communities and ecosystems. However, a widely-applicable measurement method for nocturnal light providing spatially resolved full-spectrum radiance over the full solid angle is still missing. Here, we explain the first step to fill this gap, by using a commercial digital camera with a fisheye lens to acquire vertical plane multi-spectral (RGB) images covering the full solid angle. We explain the technical and practical procedure and software to process luminance and correlated color temperature maps and derive illuminance. We discuss advantages and limitations and present data from different night-time lighting situations. The method provides a comprehensive way to characterize nocturnal light in the context of ecological light pollution. It is affordable, fast, mobile, robust, and widely-applicable by non-experts for field work.
... and the scalar illuminance for the imaging hemisphere E v, scal, hem without cosine correction [26] is defined as: ...
... please be aware that this definition is not strict and some other authors use a different value of 0.17 mcd/m 2[14,26] but the 0.25 mcd/m 2 are sometimes casually called NSU -natural sky unit. ...
Article
Artificial skyglow is a form of light pollution with wide ranging implications on the environment. The extent, intensity and color of skyglow depends on the artificial light sources and weather conditions. Skyglow can be best determined with ground based instruments. We mapped the skyglow of Berlin, Germany, for clear sky and overcast sky conditions inside and outside of the city limits. We conducted observations using a transect from the city center of Berlin towards a rural place more than 58 km south of Berlin using all-sky photometry with a calibrated commercial digital camera and a fisheye lens. From the multispectral imaging data, we processed luminance and correlated color temperature maps. We extracted the night sky brightness and correlated color temperature at zenith, as well as horizontal and scalar illuminance simultaneously. We calculated cloud amplification factors at each site and investigated the changes of brightness and color with distance, particularly showing differences inside and outside of the city limits. We found high values for illuminance above full moon light levels and amplification factors as high as 25 in the city center and a gradient towards the city limit and outside of the city limit. We further observed that clouds decrease the correlated color temperature in almost all cases. We discuss advantages and weaknesses of our method, compare the results with modeled night sky brightness data and provide recommendations for future work.
... and the scalar illuminance for the imaging hemisphere E v,scal,hem without cosine correction [26] is defined as: ...
... please be aware that this definition is not strict and some other authors use a different value of 0.17 mcd/m 2[14,26] but the 0.25 mcd/m 2 are sometimes casually called NSUnatural sky unit ...
Full-text available
Preprint
Artificial skyglow is a form of light pollution with wide ranging implications on the environment. The extent, intensity and color of skyglow depends on the artificial light sources and weather conditions. Skyglow can be best determined with ground based instruments. We mapped the skyglow of Berlin, Germany, for clear sky and overcast sky conditions inside and outside of the city limits. We conducted observations using a transect from the city center of Berlin towards a rural place more than 58 km south of Berlin using all-sky photometry with a calibrated commercial digital camera and a fisheye lens. From the multispectral imaging data, we processed luminance and correlated color temperature maps. We extracted the night sky brightness and correlated color temperature at zenith, as well as horizontal and scalar illuminance simultaneously. We calculated cloud amplification factors at each site and investigated the changes of brightness and color with distance, particularly showing differences inside and outside of the city limits. We found high values for illuminance above full moon light levels and amplification factors as high as 25 in the city center and a gradient towards the city limit and outside of the city limit. We further observed that clouds decrease the correlated color temperature in almost all cases. We discuss advantages and weaknesses of our method, compare the results with modeled night sky brightness data and provide recommendations for future work.
... All the light that escapes upwards, either reflected by surfaces on the ground or intentionally directed to the sky interacts with the atmosphere and scatters (Rayleigh scattering) causing what is called sky glow where the sky appears illuminated (Duriscoe 2016;Kyba et al. 2011). This reduces the contrast of the night sky, making astronomy optical observations difficult (Lamphar & Kocifaj 2016). ...
... That is why astronomers are amongst the early groups that are most concerned about this threat. They have been long monitoring the level of sky brightness photometrically at zenith where most of astronomical observations are conducted (Duriscoe 2016). This later progressed into all-sky mapping of sky brightness surrounding an area of interest and also development of simple device such as the handheld Sky Quality Meter (SQM) to measure sky brightness easily (Cinzano 2005). ...
Full-text available
Article
A spectral observation and analysis were conducted in order to identify the main contributor of sky brightness at two of Malaysia’s most active observatories. The light pollution observations were carried out under moonless clear night sky with a 90 mm refractor telescope and SBIG’s Self Guiding Spectrograph. We found that the main contributor to Balai Cerap Teluk Kemang (BCTK) sky brightness is High Pressure Sodium (HPS) street lighting due to its number and density used within 5 km radius of the observatory. HPS spectral lines dominate the spectrum between 556 - 640 nm, agrees with the orange hue visible to the naked eye. The intensity due to HPS lighting is so high that there was no trace of the concerned white LED spotlight less than 1 km away. However, some traces of elements from Mercury Vapor (MV) lamps at 3.6 km distance managed to reach the observatory in the green spectrum. The finding concludes that the nearby LED spotlight does not affect the night sky brightness over BCTK. Meanwhile, Langkawi National Observatory (LNO) sky profile was also observed during heavy fishing season as comparison. The sky spectra for LNO was similar to BCTK in the reds except for a very distinct peak in green region corresponding highly with green MV (532 - 547 nm) with peaks at 536 nm and 546 nm, matches the lamps used for squid fishing around the island. The intensity of the green MV light matches the intensity of HPS light sources, during the observation period of peak squid season in January. This made LNO a far less favorable condition for astronomical observing site compared to BCTK. We also found that LNO sky has brightened 3.767 times compared to finding of 2013.
... The software processes the luminance L v,sky of the sky for each pixel of the camera (luminance is commonly referred to as "brightness" referenced to human vision). The software calculates the cosine corrected illuminance E v,cos in the imaging plane: and the scalar illuminance for the imaging hemisphere E v,scal,hem without cosine correction 57 : ...
Full-text available
Article
Artificial light at night has affected most of the natural nocturnal landscapes worldwide and the subsequent light pollution has diverse effects on flora, fauna and human well-being. To evaluate the environmental impacts of light pollution, it is crucial to understand both the natural and artificial components of light at night under all weather conditions. The night sky brightness for clear skies is relatively well understood and a reference point for a lower limit is defined. However, no such reference point exists for cloudy skies. While some studies have examined the brightening of the night sky by clouds in urban areas, the published data on the (natural) darkening by clouds is very sparse. Knowledge of reference points for the illumination of natural nocturnal environments however, is essential for experimental design and ecological modeling to assess the impacts of light pollution. Here we use differential all-sky photometry with a commercial digital camera to investigate how clouds darken sky brightness at two rural sites. The spatially resolved data enables us to identify and study the nearly unpolluted parts of the sky and to set an upper limit on ground illumination for overcast nights at sites without light pollution.
... Let us denote by B ( r ) any generic radiant or photometric magnitude relevant for light-pollution studies, being r the position vector of the observing site. In the present context B ( r ) may be any member of a wide set of functions linearly related to the source radiance, e.g., the zenithal night sky brightness, the brightness in any other direction of the upper hemisphere, the average sky radiance, or the horizontal illuminance, among others [42] , including, where appropriate, their spectral density distributions. Let us further denote by L ( r , α ; λ) the spectral radiance emitted in the direction described by the two-dimensional vector α = ( z , φ ) by a source located at r , being z and φ the zenith angle and the azimuth, respectively, in the source reference frame, and λ the wavelength. ...
Article
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.
... The sky and twilight brightness were studied by Duriscoe (2016), Hanel et al. (2018) and Kishida (1989), by photoelectric measurements. Studies on dawn have been carried out using two methods: Naked eye observations and photoelectric measurements. ...
Article
The first visibility of the dawn occurs at a definite angle of the sun depression, Do which is used to calculate the fajr (dawn) prayer time. Dawn observations were carried out using Digital Single-lens Reflex (DSLR) camera in the period from February to December 2017 at several locations in both Malaysia and Indonesia (Lat. between 2.0° - 7.0° N, Long. 95.0°-106.0°E). Within the observational period, 64 days of the dawn luminance at horizon were recorded with backgrounds of both sea and land. The purpose of these observations was to determine the sun depression angle Do at the first moment when the dawn is seen using a DSLR camera. The results indicated that Do can be determined using a DSLR camera. The value of Do is between -14.5° and -18.5° with a mean value of -16.67° and standard deviation of 0.9992. This suggests that the new sun depression angle Do for dawn prayer is -17.0°. © 2018 Penerbit Universiti Kebangsaan Malaysia. All Rights Reserved.
... For instance, the input (  ) can be the spectrally integrated radiance [W·m -2 ·sr -1 ] detected by the VIIRS-DNB radiometer onboard the Suomi-NPP satellite [20][21][22][23][24][25], and the output () can be e.g. the zenithal night sky brightness in the visible band [9] or the hemispherical average of the artificial night sky brightness measured as a multiple of its reference natural value, also known as the all-sky average light pollution ratio (ALR) [14], to mention but two possible outcomes. As a matter of fact, () can be identified with any convenient photometric indicator linearly dependent on the emission of the sources, such as the luminance in any arbitrary sky direction, or the horizontal, scalar, and vertical illuminances analyzed by Duriscoe [26]. Of course, different choices for (  ) and () will require the use of different (,   ) PSF functions (that have to be specifically calculated for each case), but the general form of Eq.(1) does not change. ...
Full-text available
Article
The light pollution levels experienced at any given site generally depend on a wide number of artificial light sources distributed throughout the surrounding territory. Since photons can travel long distances before being scattered by the atmosphere, any effective proposal for reducing local light pollution levels needs an accurate assessment of the relative weight of all intervening light sources, including those located tens or even hundreds of km away. In this paper we describe several ways of quantifying and visualizing these relative weights. Particular emphasis is made on the aggregate contribution of the municipalities, which are -in many regions of the world- the administrative bodies primarily responsible for the planning and maintenance of public outdoor lighting systems
... For instance, the input ( ′ ) can be the spectrally integrated radiance [W·m −2 ·sr −1 ] detected by the VIIRS-DNB radiometer onboard the Suomi-NPP satellite [20][21][22][23][24][25], and the output ( ) can be e.g. the zenithal night sky brightness in the visible band [9] or the hemispherical average of the artificial night sky brightness measured as a multiple of its reference natural value, also known as the all-sky average light pollution ratio (ALR) [14], to mention but two possible outcomes. As a matter of fact, ( ) can be identified with any convenient photometric indicator linearly dependent on the emission of the sources, such as the luminance in any arbitrary sky direction, or the horizontal, scalar, and vertical illuminances analyzed by Duriscoe [26]. Of course, different choices for ( ′ ) and ( ) will require the use of different ( , ′ ) PSF functions (that have to be specifically calculated for each case), but the general form of Eq.(1) does not change. ...
Full-text available
Preprint
The light pollution levels experienced at any given site generally depend on a wide number of artificial light sources distributed throughout the surrounding territory. Since photons can travel long distances before being scattered by the atmosphere, any effective proposal for reducing local light pollution levels needs an accurate assessment of the relative weight of all intervening light sources, including those located tens or even hundreds of km away. In this paper we describe several ways of quantifying and visualizing these relative weights. Particular emphasis is made on the aggregate contribution of the municipalities, which are -in many regions of the world- the administrative bodies primarily responsible for the planning and maintenance of public outdoor lighting systems.
... Table 2 summarizes the different approaches and the benefits and drawbacks of each: There is presently an increasing demand for an affordable, off-the-shelf imagery system for obtaining simultaneous all-sky measurements of night sky luminance for both initial site evaluation and ongoing monitoring. Duriscoe [19] suggests a number of useful metrics that can be extracted from such spatially-resolved sky luminance data; combined with visibility studies, these may lead toward a more robust and objective means of deciding which candidates are best suited for IDA Dark Sky Place recognition. ...
Full-text available
Article
Since the invention of electric lighting in the nineteenth century, the steadily increasing use of artificial light at night in outdoor spaces has grown to threaten the integrity of dark night skies and nocturnal terrestrial spaces. The conservation community has gradually come to accept the need to protect natural nighttime darkness, which finds expression in dark sky parks and similar protected areas. As these places begin to reap tangible economic benefits in the form of sustainable ‘astrotourism,’ the movement to actively protect them gains strength. The International Dark-Sky Association designates Dark Sky Parks and Reserves under a comparative ranking scheme that assigns night sky quality tiers according to a combination of objective and subjective characteristics, but shortcomings in the consistency of these ratings exist that undermine the consistency and reputation of the designation program. Here we consider potential changes to the qualification regime to make the ratings system more robust for the benefit of future designations.
... and the scalar illuminance for the imaging hemisphere E v,scal,hem without cosine correction [36]: ...
Full-text available
Preprint
Artificial light at night has affected most of the natural nocturnal landscapes worldwide and the subsequent light pollution has diverse effects on flora, fauna and human well-being. To evaluate the environmental impacts of light pollution, it is crucial to understand both the natural and artificial components of light at night under all weather conditions. The night sky brightness for clear skies is relatively well understood and a reference point for a lower limit is defined. However, no such reference point exists for cloudy skies. While some studies have examined the brightening of the night sky by clouds in urban areas, the published data on the (natural) darkening by clouds is very sparse. Knowledge of reference points for the illumination of natural nocturnal environments however, is essential for experimental design and ecological modeling to assess the impacts of light pollution. Here we use differential all-sky photometry with a commercial digital camera to investigate how clouds darken sky brightness at two rural sites. The spatially resolved data enables us to identify and study the nearly unpolluted parts of the sky and to set an upper limit on ground illumination for overcast nights at sites without light pollution.
... Specifically, the pipeline applies basic reduction, performs photometric calibration, mosaics the images to form the panoramic views of the entire night sky, generates the models for the natural sky brightness, 2 and calculates values of various sky brightness metrics. 3 This original data pipeline was developed mainly by Dan Duriscoe about a decade ago. These scripts were written in three different languages including Python, Java, and Visual Basic. ...
Conference Paper
The US National Park Service (NPS) assesses the night sky quality over parks by capturing a series of overlapping images to obtain a mosaic view of the entire night sky. The NPS Night Skies Program has integrated a sequence of scripts and software packages (a "pipeline") to process and create the hemispherical mosaic images. This processing pipeline is being improved to reduce dependence on commercial software packages, improve management of revisions, and ease distribution of the latest version. The upgraded pipeline is designed for processing the images in three stages: (I) performing data reduction, calibration, and mosaic, (II) modeling the natural sky brightness to separate out light from artificial sources, and (III) deriving sky quality indicators. Currently, stage I is completed and is presented in detail in this report. Stage II and III are in the upgrading process and will be presented in a future report. In stage I, the pipeline applies basic image reduction, pointing registration, photometric calibration, coordinate transformation, and image mosaicking. We implemented new features including auto-logging the processing history, version control through Git and GitHub, team management on source code development, reduction on the number of required proprietary software usage, and setting the primary pipeline language to Python. Once the upgrade is completed, our open source pipeline can benefit other scientists in the similar research field worldwide for processing related sets of data.
... Let us denote by ( ) any generic radiant or photometric magnitude relevant for lightpollution studies, being the position vector of the observing site. In the present context ( ) may be any member of a wide set of functions linearly related to the source radiance, e.g., the zenithal night sky brightness, the brightness in any other direction of the upper hemisphere, the average sky radiance, or the horizontal illuminance, among others (Duriscoe, 2016), including, where appropriate, their spectral density distributions. Let us further denote by ( ′ , ′ ; ) the spectral radiance emitted in the direction described by the two-dimensional vector ′ = ( ′ , ′) by a source located at ′ , being ′ and ′ the zenith angle and the azimuth, respectively, in the source reference frame, and the wavelength. ...
Preprint
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.
... In addition to the SQM predictor variables, we converted the hemispheric SQM luminance measurements into 24 azimuthspecific illuminance values (in micro-lux units) using sine and cosine corrections (Duriscoe, 2016). These measures integrate light intensity measurements from 10 • altitude (nearest to the horizon) to 90 • altitude (zenith) into the illuminance value, and therefore the vertical AOA is 90 • . ...
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Article
Sea turtles in the Gulf of Mexico, which are listed as either threatened or endangered under the US Endangered Species Act, face numerous threats but are particularly susceptible to the negative effects of light pollution on nesting beaches. Light pollution affects the distribution, density, and placement of nests on beaches, and disrupts seafinding in hatchlings emerging from nests; often leading to their death. Rapid urban growth near Gulf Islands National Seashore (GUIS), FL, United States, over the last century has contributed to increased light pollution on its beaches. There is concern that light pollution is causing females to build nests in at-risk locations subject to erosion and flooding, and is causing the observed high rates of hatchling misorientation. From 2015 to 2016, we measured brightness of the night sky, horizon profile, and lunar variables at GUIS at loggerhead (Caretta caretta) nests to assess the effects of brightness on building of at-risk nests and hatchling misorientation. In addition, we quantified the effects of relocating at-risk nests on nest success. We found that contrast in brightness between the landward and seaward directions at GUIS was partially responsible for high rates of hatchling misorientation, and there was a strong moderating influence of lunar fraction and lunar altitude on hatchling misorientation: larger lunar fractions and lower lunar altitudes reduced misorientation. We did not find an effect of artificial light, horizon profile, or lunar fraction on the propensity of loggerheads to build nests in at-risk locations, and found no evidence that relocating nests at GUIS reduced loggerhead nest success. In fact, we found that nest success was improved and hatchling misorientation rates were reduced for relocated loggerhead nests.
... Finally, SQM or other lightmeters measure light only over a part of the sky (solid angle < 180˚) whereas vector irradiance (solid angle of 180˚) or scalar irradiance (all directions) may be more important for organisms. In this regard, hemispherical photography using fish eye lenses, which can be fitted to digital single-lens cameras, have been developed to measure full sky irradiance [38][39][40][41]. Thus, devices like SQM and luxmeters, if they can provide information in some cases, are not well-suited to assess the effect of ALAN on a broad range of organisms, especially for visual tasks in animals [42]. ...
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Article
Artificial light at night (ALAN) is an increasing phenomenon worldwide. It causes a wealth of biological and ecological effects that may eventually affect populations and ecosystems. Despite the growing concern about ALAN, little is known about the light levels species are exposed to at night, especially for wetlands and underwater habitats. We determined nocturnal irradiance in urban and peri-urban wetlands above and under water, and assessed the effect of cloud cover on the variability of ALAN across the urban gradient. Even in aquatic habitats, cloud cover could increase irradiance beyond values observed during clear full moon nights. We report a negative relationship between baseline irradiance and the increase in irradiance during overcast nights. According to this result and previous studies, we propose that the change in the variation regime of ALAN between the urban center and rural land at its periphery is a usual feature. We discuss the ecological and evolutionary implications of this spatial variation in the urban and peri-urban environment.
... These data can be used with radiative transfer models to predict night sky brightness on clear nights (Cinzano et al., 2001;Falchi et al., 2016). Both satellite imagery and the derived night sky brightness maps are used by the public to find locations for astronomical tourism (Collison and Poe, 2013;Hiscoks and Kyba, 2017), and photometric indicators of visual night sky quality can be derived from ground based hemispherical photos (Duriscoe, 2016). The global spectral shift due to adoption of white LEDs is a major challenge for astronomy, both because the blue component of white light produces more skyglow (section 2.4), and because many current ground and space-based sensors are not sensitive to blue light (section 4.5, Fig. 24). ...
Article
Remote sensing of night light emissions in the visible band offers a unique opportunity to directly observe human activity from space. This has allowed a host of applications including mapping urban areas, estimating population and GDP, monitoring disasters and conflicts. More recently, remotely sensed night lights data have found use in understanding the environmental impacts of light emissions (light pollution), including their impacts on human health. In this review, we outline the historical development of night-time optical sensors up to the current state of the art sensors, highlight various applications of night light data, discuss the special challenges associated with remote sensing of night lights with a focus on the limitations of current sensors, and provide an outlook for the future of remote sensing of night lights. While the paper mainly focuses on space borne remote sensing, ground based sensing of night-time brightness for studies on astronomical and ecological light pollution, as well as for calibration and validation of space borne data, are also discussed. Although the development of night light sensors lags behind daytime sensors, we demonstrate that the field is in a stage of rapid development. The worldwide transition to LED lights poses a particular challenge for remote sensing of night lights, and strongly highlights the need for a new generation of space borne night lights instruments. This work shows that future sensors are needed to monitor temporal changes during the night (for example from a geostationary platform or constellation of satellites), and to better understand the angular patterns of light emission (roughly analogous to the BRDF in daylight sensing). Perhaps most importantly, we make the case that higher spatial resolution and multispectral sensors covering the range from blue to NIR are needed to more effectively identify lighting technologies, map urban functions, and monitor energy use.
... (NPS) provides all-sky coverage similar to that obtained with a fisheye lens, but by mosaicking multiple wide-field images taken in succession [82,83]. The NPS image scale (93.5 arcsec / pixel) is sufficient to perform accurate stellar photometry required for calibration to known standards, and produces panoramic or fisheye 39.3 mega-pixel images. ...
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Article
Measuring the brightness of the night sky has become an increasingly important topic in recent years, as artificial lights and their scattering by the Earth’s atmosphere continue spreading around the globe. Several instruments and techniques have been developed for this task. We give an overview of these, and discuss their strengths and limitations. The different quantities that can and should be derived when measuring the night sky brightness are discussed, as well as the procedures that have been and still need to be defined in this context. We conclude that in many situations, calibrated consumer digital cameras with fisheye lenses provide the best relation between ease-of-use and wealth of obtainable information on the night sky. While they do not obtain full spectral information, they are able to sample the complete sky in a period of minutes, with colour information in three bands. This is important, as given the current global changes in lamp spectra, changes in sky radiance observed only with single band devices may lead to incorrect conclusions regarding long term changes in sky brightness. The acquisition of all-sky information is desirable, as zenith-only information does not provide an adequate characterization of a site. Nevertheless, zenith-only single-band one-channel devices such as the “Sky Quality Meter” continue to be a viable option for long-term studies of night sky brightness and for studies conducted from a moving platform. Accurate interpretation of such data requires some understanding of the colour composition of the sky light. We recommend supplementing long-term time series derived with such devices with periodic all-sky sampling by a calibrated camera system and calibrated luxmeters or luminance meters.
... The radiance for the whole dome has been integrated because the purpose is to study the contribution of the light sources in all directions. Other indicators Duriscoe (2016)). ...
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Article
Night sky brightness over Montsec Observatory (north-east of Spain) has been computed and checked against measurements using Illumina numerical model [2]. In a previous publication [20] the methodology was validated and light pollution received in the observatory coming from a unique city was computed. Here we present a simulation that includes all the sources that has a significant impact over the quality of the night sky in this area. The decision of which sources should be included in the simulations was taken following the methodology explained by [6]: using a point spread function (PSF) as a simple approach to estimate which sources are brightening the sky dome over the observer. An ad hoc PSF derived with Illumina was used with the purpose of avoiding to have to rely on already existing empirical PSF. The resulting PSF can be used in any location with similar atmospheric conditions. Differences in the spectrum of the lamps can be accounted easily by adjusting a spectrum scale factor. Illumina simulates the artificial sky brightness received (W/sr/m2) by an observer from any direction. Adding the natural sky brightness allows to compare the simulations to measurements taken with different instrumentation. In our case simulations were checked against ASTMON, SQC and SQM measurements. They show a good agreement both in absolute values and in geographical patterns for the three filters studied, B, V and R. The methodology presented opens many possibilities, such as increasing the reliability of the maps that point out the light pollution main contributors for any location, and reducing the amount of time needed to perform an accurate simulation of the night sky brightness.
... Then as night begins, the spectral composition depends on celestial bodies as the moon reflects sunlight and thus delivers a similar spectral composition to that of the day, albeit 6 orders of magnitude dimmer [19]. However, if the moon is absent, then the ambient lighting will be a result of starlight, atmospheric diffuse light, and airglow and thus middle wavelength rich [28,29]. At such low light intensities, few animals are able to perceive color and no butterfly is known to be able to perceive color at such low light levels. ...
Full-text available
Article
Light is arguably the most important abiotic factor for living organisms. Organisms evolved under specific lighting conditions and their behavior, physiology, and ecology are inexorably linked to light. Understanding light effects on biology could not be more important as present anthropogenic effects are greatly changing the light environments in which animals exist. The two biggest anthropogenic contributors changing light environments are: (1) anthropogenic lighting at night (i.e., light pollution); and (2) deforestation and the built environment. I highlight light importance for butterfly behavior, physiology, and ecology and stress the importance of including light as a conservation factor for conserving butterfly biodiversity. This review focuses on four parts: (1) Introducing the nature and extent of light. (2) Visual and non-visual light reception in butterflies. (3) Implications of unnatural lighting for butterflies across several different behavioral and ecological contexts. (4). Future directions for quantifying the threat of unnatural lighting on butterflies and simple approaches to mitigate unnatural light impacts on butterflies. I urge future research to include light as a factor and end with the hopeful thought that controlling many unnatural light conditions is simply done by flipping a switch.
... Note that many additional photometric quantities can be expressed as particular cases of equation (A1). For instance, the irradiance ( , ) within the ( ) band (units W·m  2 , or photon·s  1 ·m  2 ), produced on the input pupil of the instrument by a patch of the sky of solid angle ω can be written as ( , ) = ∫ ( ) ∫ ( , ′′, ) cos( , ′′ )d 2 ′′ d ω Λ ( 3) and the same holds for many photometric quantities routinely measured in astrophysics and light pollution research (for a description of some of the latter, see [40]). ...
Preprint
The sustained increase of emissions of artificial light is causing a progressive brightening of the night sky in most of the world. This process represents a threat for the long-term sustainability of the scientific and educational activity of ground-based astronomical observatories operating in the optical range. Huge investments in building, scientific and technical workforce, equipment and maintenance can be at risk if the increasing light pollution levels hinder the capability of carrying out the top-level scientific observations for which these key scientific infrastructures were built. In addition, light pollution has other negative consequences, as e.g. biodiversity endangering and the loss of the starry sky for recreational, touristic, and cultural enjoyment. The traditional light pollution mitigation approach is based on imposing conditions on the photometry of individual sources, but the aggregated effects of all sources in the territory surrounding the observatories are seldom addressed in the regulations. We propose that this approach shall be complemented with a top-down, inmission limits strategy, whereby clear limits are established to the admissible deterioration of the night sky above the observatories. We describe the general form of the indicators that can be employed to this end, and develop linear models relating their values to the artificial emissions across the territory. This approach can be extended to take into account for other protection needs, and it is expected to be useful for making informed decisions on public lighting, in the context of wider spatial planning projects.
... An techically simpler but still highly useful approach is all-sky imaging in the Johnson-Cousins B, V and R bands [24][25][26][27], or conventional DSLR RGB imagery [28][29]. The all-sky photopic brightness evaluated in the V(λ) band or, as an approximation, in the Johnson-Cousins V, allows to calculate a relevant set of visual parameters at the observer's site [30]. ...
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Article
A recurring question arises when trying to characterize, by means of measurements or theoretical calculations, the zenithal night sky brightness throughout a large territory: how many samples per square kilometer are needed? The optimum sampling distance should allow to reconstruct with sufficient accuracy the continuous zenithal brightness map across the whole region, whilst at the same time avoiding an unnecessary and redundant oversampling. This paper attempts to provide some tentative answers to this issue, using two complementary tools: the luminance structure function and the Nyquist-Shannon spatial sampling theorem. The anaysis of several regions of the world, based on the data of the New world atlas of artificial night sky brightness (Falchi et al 2016, Sci. Adv. 2, e1600377) suggests that, as a rule of thumb, about one measurement per square kilometer could be sufficient for determining the zenithal night sky brightness of artificial origin at any point of a region to within 0.1 mag/arcsec^2 (in the root-mean-square sense) of its true value in the Johnson-Cousins V band. The exact reconstruction of the zenithal night sky brightness maps from samples taken at the Nyquist rate seems to be considerably more demanding.
... ð v L T (r,a 00 , l) cos(a,a 00 )d 2 a 00 dl, ðA 3Þ and the same holds for many photometric quantities routinely measured in astrophysics and light pollution research (for a description of some of the latter, see [43]). ...
Full-text available
Article
The persistent increase of artificial light emissions is causing a progressive brightening of the night sky in most regions of the world. This process is a threat for the long-term sustainability of the scientific and educational activity of ground-based astronomical observatories operating in the optical range. Huge investments in building, scientific and technical workforce, equipment and maintenance can be at risk if the increasing light pollution levels hinder the capability of carrying out the top-level scientific observations for which these key scientific infrastructures were built. Light pollution has other negative consequences, as e.g. biodiversity endangering and the loss of the starry sky for recreational, touristic and preservation of cultural heritage. The traditional light pollution mitigation approach is based on imposing conditions on the photometry of individual sources, but the aggregated effects of all sources in the territory surrounding the observatories are seldom addressed in the regulations. We propose that this approach shall be complemented with a top-down, ambient artificial skyglow immission limits strategy, whereby clear limits are established to the admissible deterioration of the night sky above the observatories. We describe the general form of the indicators that can be employed to this end, and develop linear models relating their values to the artificial emissions across the territory. This approach can be easily applied to other protection needs, like e.g. to protect nocturnal ecosystems, and it is expected to be useful for making informed decisions on public lighting, in the context of wider spatial planning projects.
... To develop a clear picture of the diverse phenomenon resulting from ALAN, ground based sensing of light at night is critical. A number of instruments have been used to collect data on the quantity and form of light at night in a range of environments [1][2][3][4]. These instruments vary from inexpensive single point sensors [5,6], off-the-shelf digital cameras equipped with fish-eye lenses [7], to custom built systems with a range of cost and capabilities [8]. ...
Full-text available
Article
Instrumentation developed to monitor and characterize light pollution from the ground has helped frame our understanding of the impacts of artificial light at night (ALAN) [Bará, Lima, & Zamorano, 2019; Hänel et al., 2018; Zamorano et al., 2017]. All-sky imaging has been used to quantify and characterize ALAN in a variety of environments [D. M. Duriscoe, 2016; Jechow, Kyba, & Hölker, 2019]. Over the past decade growth in access to DIY electronics has afforded the opportunity for the development of new and affordable instrumentation for ALAN research. The GONet (Ground Observing Network) camera is an inexpensive (~USD 100), simple to use, all-sky imaging system designed to allow measurements of sky quality at night. Due to their ease of use and low price, GONet cameras allow observations by users with little technical expertise, large inter-comparison campaigns and deployments of opportunity. Developed as a student engineering project at the Adler Planetarium, initial field tests of the GONet system have demonstrated its utility as a tool that can benefit ALAN research. Here we present an overview of the design and use of the GONet device, methods of calibration, initial results from observations, potential use cases, and limitations of the system. What we describe here is the version 1 GONet camera. We conclude with a brief description of the version 2 unit already under development.
... Refs. [7] and [8]), but others may be of greater interest to assess the quality of the night sky and night environment: average radiance in the whole night sky, average radiance at 30 • above the horizon, average radiance in the first 10 • above the horizon, total horizontal irradiance, average vertical irradiance, maximum radiance at a particular zenith distance or in the whole sky hemisphere, and others (some are discussed in Ref. [9]). ...
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Article
Light pollution modeling and monitoring has traditionally used zenith sky brightness as its main indicator. Several other indicators (e.g., average sky radiance, horizontal irradiance, and average sky radiance at given interval of zenith distances) may be more useful, both for general and specific purposes of ecology studies, night sky, and environmental monitoring. These indicators can be calculated after the whole sky radiance is known with sufficient angular detail. This means, for each site, to integrate the contribution in each direction of the sky of each light source in the radius of hundreds of km. This approach is extremely high time-consuming if the mapping is desired for a large territory. Here, we present a way to obtain maps of large territories for a large subset of useful indicators, bypassing the need to calculate first the radiance map of the whole sky in each site to obtain from it the desired indicator in that site. For each indicator, a point spread function (PSF) is calculated from the whole sky radiance maps generated by a single source at sufficiently dense number of distances from the observing site. If the PSF is transversally shift-invariant, that is, if it depends only on the relative position of source and observer, then we can further speed up the map calculation via the use of fast Fourier-transform. We present here examples of maps for different indicators. Precise results can be calculated for any single site, taking into account the site and light sources' altitudes, by means of specific inhomogeneous (spatially variant) and anisotropic (nonrotationally symmetric) PSFs.
... We quantify this change with the sky brightness metrics derived from the images. Five indicators (Duriscoe, 2016) based on the observed panoramic images focus on different aspects of sky brightness: horizontal illuminance, maximum vertical illuminance, zenith brightness, percentage of lost stars, and all-sky light pollution ratio (ALR). Illuminance, the amount of visible light incident on a unit surface area, quantifies how brightly the landscape is lit from the night sky. ...
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Preprint
The US National Park Service (NPS) Night Skies Program measured changes in sky brightness resulting from a countywide lighting retrofit project. The retrofit took place in Chelan County, a gateway community to North Cascades National Park and Lake Chelan National Recreation Area in Washington State. The county retrofitted all 3,693 county-owned high pressure sodium (HPS) street lamps to full cutoff LEDs. This number is about 60% of the County's total outdoor street and area lights. About 80% of the newly installed lights were 3000K in color temperature and 20% were 4000K. The 4000K LEDs were used to meet Washington State Department of Transportation guidelines. To measure sky brightness, we used the NPS night sky camera system before the retrofit started in 2018 and after its completion in 2019. These images were photometrically calibrated and mosaicked together to provide hemispherical images in V band. For comparison with our ground-based measurement, we obtained the satellite imagery taken by Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership satellite. Our measurements show that the post-retrofit skyglow became brighter and extended higher in the sky, but upward radiance, as measured by the day-night band radiometer, decreased. These divergent results are likely explained by a substantial increase in light emitted at wavelengths shorter than 500 nm, and a relative decrease in zenith light emission due to better shielded luminaires. These results also demonstrate that earlier models relating VIIRS day-night band data to skyglow will, at a minimum, require substantial revision to account for the different characteristics of solid state luminaires.
... The situation is again somewhat easier to handle when it comes to artificial night sky brightness in observatories or dark sky destinations. Several useful indicators, like the zenith brightness, the average hemispheric radiance, the average radiance within altitude bands above the horizon, and others, are already in use ( Duriscoe, 2016 ;Bará, 2020 , 2021 ). The artificial sky radiance is routinely measured in observatories in multiple instrumental bands, see e.g. ...
Article
The prevailing regulatory framework for light pollution control is based on establishing conditions on individual light sources or single installations (regarding features like ULOR, spectrum, illuminance levels, glare, ...), in the hope that an ensemble of individually correct lighting installations will be effective to somehow solve this problem. This "local sources" approach is indeed necessary, and shall no doubt be enforced; however, it seems to be clearly insufficient for curbing the actual process of degradation of the night, and for effectively attaining the necessary remediation goals. In this paper we describe a complementary (not substitutive) 'red-lines' strategy that should in our opinion be adopted as early as possible in the policies for light pollution control. It is based on setting maximum values for absolute light pollution indicators and using linear models relating the indicators to the source emissions in order to establish the maximum light emissions compatible with these red-lines. This top-down approach seeks to set definite limits on the allowable degradation of the night, providing the methodological tools required for making science-informed public policy decisions and for managing the transition processes. Light pollution abatement should routinely be included as an integral part of any territorial management plan. A practical application case-study based on the night sky brightness at zenith is described to illustrate these concepts.
... The horizontal irradiance, ho we ver, is not the only useful indicator that can be derived from the radiance field. Other radiance-related indicators are appropriate for different kinds of studies, including the av erage all-sk y radiance, the average radiance at intermediate zenith distances, or the average radiance in the first degrees of altitude abo v e the horizon rim (Duriscoe 2016 ;Falchi & Bar á 2021 ). ...
Preprint
Estimating the horizontal irradiance from measurements of the zenith night sky radiance is a useful operation for basic and applied studies in observatory site assessment, atmospheric optics and environmental sciences. The ratio between these two quantities, also known as Posch ratio, has been previously studied for some canonical cases and reported for a few observational sites. In this work we (a) generalize the Posch ratio concept, extending it to any pair of radiance-related linear indicators, (b) describe its main algebraic properties, and (c) provide analytical expressions and numerical evaluations for its three basic nighttime components (moonlight, starlight and other astrophysical light sources, and artificial light). We show that the horizontal irradiance (or any other linear radiance indicator) is generally correlated with the zenith radiance, enabling its estimation from zenith measurements if some a priori information on the atmospheric state is available.
... and the scalar illuminance for the imaging hemisphere E v, scal, hem without cosine correction [29] : ...
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Article
Artificial skyglow is dynamic due to changing atmospheric conditions and the switching on and off of artificial lights throughout the night. Street lights as well as the ornamental illumination of historical sites and buildings are sometimes switched off at a certain time to save energy. Ornamental lights in particular are often directed upwards, and can therefore have a major contribution towards brightening of the night sky. Here we use differential photometry to investigate the change in night sky brightness and illuminance during an automated regular switch-off of ornamental light in the town of Balaguer and an organized switch-off of all public lights in the village of Àger, both near Montsec Astronomical Park in Spain. The sites were observed during two nights with clear and cloudy conditions using a DSLR camera and a fisheye lens. A time series of images makes it possible to track changes in lighting conditions and sky brightness simultaneously. During the clear night, the ornamental lights in Balaguer contribute over 20% of the skyglow at zenith at the observational site. Furthermore, we are able to track very small changes in the ground illuminance on a cloudy night near Àger.
Article
Estimating the horizontal irradiance from measurements of the zenith night-sky radiance is a useful operation for basic and applied studies in observatory site assessment, atmospheric optics, and environmental sciences. The ratio between these two quantities, also known as the Posch ratio, has previously been studied for some canonical cases and reported for a few observational sites. In this work we (a) generalize the Posch ratio concept, extending it to any pair of radiance-related linear indicators, (b) describe its main algebraic properties, and (c) provide analytical expressions and numerical evaluations for its three basic night-time components (moonlight, starlight and other astrophysical light sources, and artificial light). We show that the horizontal irradiance (or any other linear radiance indicator) is generally correlated with the zenith radiance, enabling its estimation from zenith measurements if some a priori information on the atmospheric state is available.
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Article
A new portable sky scanner designed for low-light-level detection at night is developed and employed in night sky brightness measurements in a rural region. The fast readout, adjustable sensitivity and linear response guaranteed in 5–6 orders of magnitude makes the device well suited for narrow-band photometry in both dark areas and bright urban and suburban environments. Quasi-monochromatic night-sky brightness data are advantageous in the accurate characterization of spectral power distribution of scattered and emitted light and, also allows for the possibility to retrieve light output patterns from whole-city light sources. The sky scanner can operate in both night and day regimes, taking advantage of the complementarity of both radiance data types. Due to its inherent very high sensitivity the photomultiplier tube could be used in night sky radiometry, while the spectrometer-equipped system component capable of detecting elevated intensities is used in daylight monitoring. Daylight is a source of information on atmospheric optical properties that in turn are necessary in processing night sky radiances. We believe that the sky scanner has the potential to revolutionize night-sky monitoring systems.
Article
Pourtant d’apparence immuable, le ciel étoilé est aujourd’hui menacé de disparition. La cause est la croissance généralisée de la pollution lumineuse, résultat de l’utilisation de dispositifs d’éclairage inadéquats. Nous présentons ici les résultats de la mesure de cette pollution obtenue par différentes approches méthodologiques sur le territoire de la Réserve internationale de ciel étoilé du Mont-Mégantic (RICEMM). La RICEMM a été créée en 2007 afin de protéger la qualité des observations astronomiques et de recherche de l’observatoire du mont Mégantic, ainsi que pour conserver les paysages étoilés exceptionnels du site. Deux aspects incontournables de la lumière artificielle nocturne ont été pris en compte : ses sources, ainsi que sa diffusion dans l’atmosphère. Les analyses démontrent que le niveau de pollution lumineuse est resté stable depuis 10 ans dans la RICEMM, tant au zénith que pour l’ensemble du ciel, et ce, malgré une tendance mondiale à la hausse des niveaux d’éclairement, l’augmentation de la population dans la périphérie du parc national du Mont-Mégantic et l’arrivée sur le marché de types de luminaires problématiques.
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Exposure to artificial light at night (ALAN) is a significant factor in ecological and epidemiological research. Although levels of exposure are frequently estimated from satellite-based measurements of upward radiance, and the correlation between upward radiance and zenith sky brightness is established, the correlation between upward radiance and the biologically relevant exposure to light experienced from all directions on the ground has not been investigated. Because ground-based exposure to ALAN can depend on local glare sources and atmospheric scattering, ecological and epidemiological studies using upward radiance have relied on an untested relationship. To establish the nature of the relationship between upward radiance and hemispherical scalar illuminance (SI) on the ground and to calibrate future experimental studies of ALAN, we used hemispheric digital photography to measure SI at 515 locations in coastal southern California, and compared those values to co-located satellite-based measures of upward radiance as described by the Visible Infrared Imaging Radiometer Suite (VIIRS) satellite’s Day-Night Band (DNB) sensor and zenith downwards radiance as estimated by the World Atlas of Artificial Night Sky Brightness (WA). We found significant variations in SI within the geographic scale defined by the resolutions of both the DNB and WA, as well as in both luminance and color correlated temperature (CCT) across individual image hemispheres. We observed up to two or more orders of magnitude in ALAN exposure within any given satellite-measured unit. Notwithstanding this variation, a linear model of log(SI) (log(SI modeled )), dependent only on the percent of the image hemisphere obscured by structures along the horizon (percent horizon) and log(WA) accounted for 76% of the variation in observed log(SI). DNB does not perform as well in alternative models and consequently future studies seeking to characterize the light environment should be built on WA data when the high temporal resolution of DNB measurements are not needed.
Preprint
Initial details and results from the Ground Observation Network (GONet) all-sky nighttime imaging system. GONet is an automated method of collecting night sky quality data with RGB information throughout a night. The system was designed with a target cost of $100 USD.
Article
The US National Park Service (NPS) Night Skies Program measured changes in sky brightness resulting from a countywide lighting retrofit project. The retrofit took place in Chelan County, a gateway community to North Cascades National Park and Lake Chelan National Recreation Area in Washington State. The county retrofitted all 3693 county-owned high pressure sodium (HPS) street lamps to full cutoff LEDs. This number is about 60% of the County's total outdoor street and area lights. About 80% of the newly installed lights were 3000 K in color temperature and 20% were 4000 K. The 4000 K LEDs were used to meet Washington State Department of Transportation guidelines. To measure sky brightness, we used the NPS night sky camera system before the retrofit started in 2018 and after its completion in 2019. These images were photometrically calibrated and mosaicked together to provide hemispherical images in V band. For comparison with our ground-based measurement, we obtained the satellite imagery taken by Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership satellite. Our measurements show that the post-retrofit skyglow became brighter and extended higher in the sky, but upward radiance, as measured by the day-night band radiometer, decreased. These divergent results are likely explained by a substantial increase in light emitted at wavelengths shorter than 500 nm, and a relative decrease in upward light emission due to better shielded luminaires. These results also demonstrate that earlier models relating VIIRS day-night band data to skyglow will – at a minimum – require substantial revision to account for the different characteristics of solid state luminaires.
Article
Studying light pollution is an interest to researchers in a wide range of fields including astronomy, biology, civil engineering, ecology, and social science. Consequently, numerous sky brightness metrics have been developed over the years. However, what metrics are truly representative of the night sky quality and unique to the measured feature? The US National Park Service Night Skies Program has collected more than 1,500 sets of night skies data throughout the United States. For each data set, a maximum of 56 metrics were measured through the combination of the captured images, Sky Quality Meter readings, and visual observations. This paper analyzes these measurements and identifies a distinctive set of night sky brightness metrics based on the principal component analysis. Three major findings emerge. First, the commonly used metrics, such as the zenith brightness, horizontal illuminance, maximum vertical illuminance, all-sky light pollution ratio, Bortle class, and limiting magnitude, are highly correlated. Second, the observed sky brightness often offers a good estimate of the artificial light level despite the natural varying night sky background. Third, a set of six metrics that consists of the zenith brightness and sky brightness percentiles are more distinctive when used to concisely describe night sky characteristics. These findings suggest that long-term night sky monitoring can be efficiently carried out by measuring the sky brightness percentiles on the observed all-sky images.
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Quietn ess exists in place s without human induc ed noise sources and could off er multip le be nefi ts to citizen s. Unlit areas are sites free of huma n intense interference at ni ght t ime. The aim of thi s research is to develop an in tegrated environme ntal index of noi se an d light poll ution. In order to achi eve this goal the spa tial pattern of quietn ess and darkness of Europe was identifi ed, as well as their overlap. The environme ntal in dex revealed t hat the spa tial patterns of Quiet and Unl it Areas differ to a great extent highlig hting the importa nce of preserving quietn ess as well as darkness in EU. The spatial overlap of these t wo environmental characteristics cover s 32.0 6% of EU surface area, which could be cons idered a feasibl e threshold for protection. This diu rnal and noctur nal metric of environme ntal quality accompanied with all direct and indirect benefi ts to huma n well-being cou ld indicate a target for environme ntal protection in the EU poli cy and practices
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Natural transitions between light and darkness influence the biology and behaviour of many organisms. What happens when humans introduce light into darkness? Oceanic beaches, where sea turtles nest, provide an example of both the problem and approaches to its solution.
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Despite constituting a widespread and significant environmental change, understanding of artificial nighttime skyglow is extremely limited. Until now, published monitoring studies have been local or regional in scope, and typically of short duration. In this first major international compilation of monitoring data we answer several key questions about skyglow properties. Skyglow is observed to vary over four orders of magnitude, a range hundreds of times larger than was the case before artificial light. Nearly all of the study sites were polluted by artificial light. A non-linear relationship is observed between the sky brightness on clear and overcast nights, with a change in behavior near the rural to urban landuse transition. Overcast skies ranged from a third darker to almost 18 times brighter than clear. Clear sky radiances estimated by the World Atlas of Artificial Night Sky Brightness were found to be overestimated by ~25%; our dataset will play an important role in the calibration and ground truthing of future skyglow models. Most of the brightly lit sites darkened as the night progressed, typically by ~5% per hour. The great variation in skyglow radiance observed from site-to-site and with changing meteorological conditions underlines the need for a long-term international monitoring program.
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The effects of artificial light at night are an emergent research topic for astronomers, physicists, engineers and biologists around the world. This leads to a need for measurements of the night sky brightness (= diffuse luminance of the night sky) and nocturnal illuminance. Currently, the most sensitive light meters measure the zenith sky brightness in magV/arcsec2 or – less frequently – in cd m−2. However, the horizontal illuminance resulting only from the night sky is an important source of information that is difficult to obtain with common instruments. Here we present a set of approximations to convert the zenith luminance into horizontal illuminance. Three different approximations are presented for three idealized atmospheric conditions: homogeneous sky brightness, an isotropically scattering atmosphere and a turbid atmosphere. We also apply the resulting conversion formulae to experimental data on night sky luminance, obtained during the past three years.
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The standard visibility model in light pollution studies is the formula of Hecht (1947), as used e.g. by Schaefer (1990). However it is applicable only to point sources and is shown to be of limited accuracy. A new visibility model is presented for uniform achromatic targets of any size against background luminances ranging from zero to full daylight, produced by a systematic procedure applicable to any appropriate data set (e.g Blackwell (1946)), and based on a simple but previously unrecognized empirical relation between contrast threshold and adaptation luminance. The scotopic luminance correction for variable spectral radiance (colour index) is calculated. For point sources the model is more accurate than Hecht's formula and is verified using telescopic data collected at Mount Wilson by Bowen (1947), enabling the sky brightness at that time to be determined. The result is darker than the calculation by Garstang (2004), implying that light pollution grew more rapidly in subsequent decades than has been supposed. The model is applied to the nebular observations of William Herschel, enabling his visual performance to be quantified. Proposals are made regarding sky quality indicators for public use.
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In 2007, the area around the Mont-Mégantic Observatory (MMO) was officially certified by the International Dark-Sky Association and the Royal Astronomy Association of Canada as the first International Dark Sky Reserve (IDSR). In order to be able to investigate the impact of Artificial Light at Night on night sky brightness before and after the establishment of the IDSR, we used a heterogeneous artificial sky brightness model including an implicit calculation of 2nd order scattering (ILLUMINA) developed by Martin Aubé's group. This model generates three kinds of outputs: the sky radiance at the given site, observing angle and wavelength and the corresponding contribution and sensitivity maps. The maps allow for the identification of the origin of the sky radiance according to each part of the surrounding territory. For summer clear sky conditions, the results show that replacing light fixtures within a 25 km radius around the MMO with cut-off High Pressure Sodium devices and reducing the total installed radiant power to ∼40% of its initial level are very efficient ways of reducing artificial sky brightness. The artificial sky brightness reduction at zenith observed after the establishment of the IDSR was ∼50% in the 546 nm mercury spectral line, while the reduction obtained in the 569 nm sodium line was ∼30%. A large part of that reduction can be associated to the reduction in radiant power. The contribution and sensitivity maps highlight critical zones where any changes in the lighting infrastructure have the most important impact on sky brightness at the MMO. Contribution and sensitivity maps have been used to analyze the detailed origin of sky brightness reduction. The results of this study are intended to support authorities in the management of their lighting infrastructure with the goal of reducing sky brightness. The results have been shared with MMO officials and are being used as a tool to improve sky quality at the observatory.
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Anthropogenic sky glow (a result of light pollution) combines with the natural background brightness of the night sky when viewed by an observer on the earth’s surface. In order to measure the anthropogenic component accurately, the natural component must be identified and subtracted. A model of the moonless natural sky brightness in the V-band was constructed from existing data on the Zodiacal Light, an airglow model based on the van Rhijn function, and a model of integrated starlight (including diffuse galactic light) constructed from images made with the same equipment used for sky brightness observations. The model also incorporates effective extinction by the atmosphere and is improved at high zenith angles (>80°) by the addition of atmospheric diffuse light. The model may be projected onto local horizon coordinates for a given observation at a resolution of 0.05° over the hemisphere of the sky, allowing it to be accurately registered with data images obtained from any site. Zodiacal Light and integrated starlight models compare favorably with observations from remote dark sky sites, matching within ± 8 nL over 95% of the sky. The natural airglow may be only approximately modeled, errors of up to ± 25 nL are seen when the airglow is rapidly changing or has considerable character (banding); ± 8 nL precision may be expected under favorable conditions. When subtracted from all-sky brightness data images, the model significantly improves estimates of sky glow from anthropogenic sources, especially at sites that experience slight to moderate light pollution.
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The development of street lamps based on solid-state lighting technology is likely to introduce a major change in the colour of urban skyglow (one form of light pollution). We demonstrate the need for long-term monitoring of this trend by reviewing the influences it is likely to have on disparate fields. We describe a prototype detector which is able to monitor these changes, and could be produced at a cost low enough to allow extremely widespread use. Using the detector, we observed the differences in skyglow radiance in red, green and blue channels. We find that clouds increase the radiance of red light by a factor of 17.6, which is much larger than that for blue (7.1). We also find that the gradual decrease in sky radiance observed on clear nights in Berlin appears to be most pronounced at longer wavelengths.
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Natural resource managers have used natural variability concepts since the early 1960s and are increasingly relying on these concepts to maintain biological diversity, to restore ecosystems that have been severely altered, and as benchmarks for assessing anthropogenic change. Management use of natural variability relies on two concepts: that past conditions and processes provide context and guidance for managing ecological systems today, and that disturbance-driven spatial and temporal variability is a vital attribute of nearly all ecological systems. We review the use of these concepts for managing ecological systems and landscapes. We conclude that natural variability concepts provide a framework for improved un- derstanding of ecological systems and the changes occurring in these systems, as well as for evaluating the consequences of proposed management actions. Understanding the history of ecological systems (their past composition and structure, their spatial and temporal variability, and the principal processes that influenced them) helps managers set goals that are more likely to maintain and protect ecological systems and meet the social values desired for an area. Until we significantly improve our understanding of ecological systems, this knowledge of past ecosystem functioning is also one of the best means for predicting impacts to ecological systems today. These concepts can also be misused. No a priori time period or spatial extent should be used in defining natural variability. Specific goals, site-specific field data, inferences derived from data collected elsewhere, simulation models, and explicitly stated value judg- ment all must drive selection of the relevant time period and spatial extent used in defining natural variability. Natural variability concepts offer an opportunity and a challenge for ecologists to provide relevant information and to collaborate with managers to improve the management of ecological systems.
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Benchmarks provide context and are a critical element of all ecological assessments. Over the last 25 y, hundreds of papers have been published on various aspects of ecological assessments, and most of the analyses described in these papers depend on specifying an ecological benchmark for context. Freshwater scientists and managers usually use reference sites (typically sites in natural or least-disturbed condition) to assess the ecological conditions at other sites. Accurate and precise assessments require that assessed sites be matched with appropriate reference conditions. Two general types of approaches have been proposed to predict reference conditions: classifications based on natural environmental settings and models that use continuously variable environmental attributes as inputs. Two types of classifications have been examined: geographic-dependent regionalizations based on general landscape features and geographic-independent typologies that are typically based on combinations of regional and channel features. We examined >1000 papers that addressed some aspect of predicting the reference condition in freshwater ecosystems. We focused on 5 types of benchmarks: ecological, thermal, hydrologic, geomorphic, and chemical. Our review showed that over the last 25 y, researchers have developed increasingly sophisticated methods that can be used to predict reference conditions. Most disciplines have increasingly moved toward site-specific modeling approaches as a way to improve both accuracy and precision of predictions, although typological approaches dominate geomorphic characterizations. Papers published in J-NABS have been especially important in advancing and refining methods for predicting ecological benchmarks. Much of the progress made in the science of ecological assessment emerged from research that advanced our understanding of how the spatial and temporal distributions of freshwater biota are related to naturally occurring environmental features and how those relationships can be most accurately and precisely described and predicted. Thus, the performance of ecological assessments is critically linked to how well we characterize freshwater environments, and research in the watershed sciences that addresses predicting thermal, hydrologic, geomorphic, and chemical attributes of freshwater ecosystems has paralleled research focused on predicting biota. We anticipate that knowledge produced from future collaborations between ecologists and watershed scientists coupled with the application of modern modeling techniques will largely determine progress in characterizing and predicting biota–environment relationships and, thus, the accuracy and precision of future ecological assessments.
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Artificial light is globally one of the most widely distributed forms of anthropogenic pollution. However, while both the nature and ecological effects of direct artificial lighting are increasingly well documented, those of artificial sky glow have received little attention. We investigated how city lights alter natural regimes of lunar sky brightness using a novel ten month time series of measurements recorded across a gradient of increasing light pollution. In the city, artificial lights increased sky brightness to levels six times above those recorded in rural locations, nine and twenty kilometers away. Artificial lighting masked natural monthly and seasonal regimes of lunar sky brightness in the city, and increased the number and annual regime of full moon equivalent hours available to organisms during the night. The changes have potentially profound ecological consequences.
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We describe a simple apparatus for making measurements of night sky brightness as a function of zenith and azimuth using "off-the-shelf" equipment: a Unihedron Sky Quality Meter with Lens, a protractor with plumb-line, a tripod, and a hand-held compass. Compared to a photoelectric or CCD photometric system, this apparatus is simple to set up and use and does not require complex data reduction procedures. Thus, this apparatus makes measurements of night sky brightness as a function of zenith and azimuthal angles quite amenable to students.
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One of the first 'International Dark-sky Parks' in Europe was established at the Zselic Landscape Protection Area in Hungary. A special monitoring program has been carrying on to survey the quality of the night sky using 'Sky Quality Meters' and DSLR cameras. The main conclusion of our measurements is that the local villages have only a minimal effect on the quality of the sky. There are light-domes due to the neighbouring cities only close to the horizon, the main source of obtrusive light is the city of Kaposvár. The anthropogenic component of zenith luminance of the night sky is obtained as the function of the distance from the city centre of Kaposvár. Our data were modelled by radiation transfer calculations. These results can help to draw attention to the energy emitted useless to the space and to protect our nocturnal landscape of nature parks for the next generations.
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Artificial lighting disrupts the nocturnal orientation of sea turtle hatchlings as they crawl from their nest to the ocean. Laboratory experiments in an arena were used to simultaneously present artificial light (that attracted the turtles toward “land”) and natural cues (a dark silhouette of the dune behind the beach) that promoted “seaward” orientation. Artificial lighting disrupted seaward crawling in the presence of low silhouettes, but not high silhouettes. Low silhouettes provided adequate cues for seaward crawling when the apparent brightness of artificial light was reduced. Based upon these results, we postulate that artificial light disrupts orientation by competing with natural cues. Current restoration practices at nesting beaches emphasize light reduction. However at many sites some lights cannot be modified. Our results suggest that pairing dune restoration (to enhance natural cues) with light reduction (to the extent possible) should significantly improve hatchling orientation, even at nesting beaches where lighting cannot be entirely eliminated.
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Ecologists have long studied the critical role of natural light in regulating species interactions, but, with limited exceptions, have not investigated the consequences of artificial night lighting. In the past century,the extent and intensity of artificial night lighting has increased such that it has substantial effects on the biology and ecology of species in the wild. We distinguish “astronomical light pollution”, which obscures the view of the night sky, from “ecological light pollution”, which alters natural light regimes in terrestrial and aquatic ecosystems. Some of the catastrophic consequences of light for certain taxonomic groups are well known, such as the deaths of migratory birds around tall lighted structures, and those of hatchling sea turtles disoriented by lights on their natal beaches. The more subtle influences of artificial night lighting on the behavior and community ecology of species are less well recognized, and constitute a new focus for research in ecology and a pressing conservation challenge.
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We present here the All Sky Transmission MONitor (ASTMON), designed to perform a continuous monitoring of the surface brightness of the complete night-sky in several bands. The data acquired are used to derive, in addition, a subsequent map of the multiband atmospheric extinction at any location in the sky, and a map of the cloud coverage. The instrument has been manufactured to afford extreme weather conditions, and remain operative. Designed to be fully robotic, it is ideal to be installed outdoors, as a permanent monitoring station. The preliminary results based on two of the currently operative units (at Do\~nana National Park - Huelva- and at the Calar Alto Observatory - Almer\'ia -, in Spain), are presented here. The parameters derived using ASTMON are in good agreement with previously reported ones, what illustrates the validity of the design and the accuracy of the manufacturing. The information provided by this instrument will be presented in forthcoming articles, once we have accumulated a statistically amount of data.
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Results of the first comprehensive light pollution survey in Hong Kong are presented. The night-sky brightness was measured and monitored around the city using a portable light-sensing device called the Sky Quality Meter over a 15-month period beginning in March 2008. A total of 1,957 data sets were taken at 199 distinct locations, including urban and rural sites covering all 18 Administrative Districts of Hong Kong. The survey shows that the environmental light pollution problem in Hong Kong is severe-the urban night skies (sky brightness at 15.0 mag arcsec(- 2)) are on average ~ 100 times brighter than at the darkest rural sites (20.1 mag arcsec(- 2)), indicating that the high lighting densities in the densely populated residential and commercial areas lead to light pollution. In the worst polluted urban location studied, the night-sky at 13.2 mag arcsec(- 2) can be over 500 times brighter than the darkest sites in Hong Kong. The observed night-sky brightness is found to be affected by human factors such as land utilization and population density of the observation sites, together with meteorological and/or environmental factors. Moreover, earlier night skies (at 9:30 p.m. local time) are generally brighter than later time (at 11:30 p.m.), which can be attributed to some public and commercial lightings being turned off later at night. On the other hand, no concrete relationship between the observed sky brightness and air pollutant concentrations could be established with the limited survey sampling. Results from this survey will serve as an important database for the public to assess whether new rules and regulations are necessary to control the use of outdoor lightings in Hong Kong.
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We describe a system for rapidly measuring the brightness of the night sky using a mosaic of CCD images obtained with a low-cost automated system. The portable system produces millions of independent photometric measurements covering the entire sky, enabling the detailed characterization of natural sky conditions and light domes produced by cities. The measurements are calibrated using images of standard stars contained within the raw data, producing results closely tracking the Johnson V astronomical standard. The National Park Service has collected hundreds of data sets at numerous parks since 2001 and is using these data for the protection and monitoring of the night-sky visual resource. This system also allows comprehensive characterization of sky conditions at astronomical observatories. We explore photometric issues raised by the broadband measurement of the complex and variable night-sky spectrum, and potential indices of night-sky quality. Comment: 22 pages, 16 figures; replaced missing/duplicated pages
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Keeping It Wild 2 is an interagency strategy to monitor trends in selected attributes of wilderness character based on lessons learned from 15 years of developing and implementing wilderness character monitoring across the National Wilderness Preservation System. This document updates and replaces Keeping It Wild: An Interagency Strategy for Monitoring Wilderness Character Across the National Wilderness Preservation System (Landres and others 2008), and provides a foundation for agencies to develop a nationally consistent approach to implement this monitoring. This monitoring strategy addresses two questions: How do stewardship activities affect attributes of wilderness character? How are attributes selected as integral to wilderness character changing over time within a wilderness, within an agency, and across the National Wilderness Preservation System? The primary audiences for the information from this monitoring are agency staff who manage wilderness day-to-day, and regional and national staff who develop wilderness policy and assess its effectiveness. The results of this monitoring will provide these staff some of the key data they need to improve wilderness stewardship and wilderness policy. Keeping It Wild 2 is designed to be nationally consistent across the four wilderness managing agencies and locally relevant, to be cost-effective, and to facilitate communication across the many resource programs that are responsible for preserving wilderness character. Implementing this monitoring strategy does not guarantee the preservation of wilderness character, but it informs and improves wilderness stewardship, and ensures managers are accountable to the central mandate of the 1964 Wilderness Act—to preserve wilderness character.
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Change in day length is an important cue for reproductive activation in seasonally breeding animals to ensure that the timing of greatest maternal investment (e.g. lactation in mammals) coincides with favourable environmental conditions (e.g. peak productivity). However, artificial light at night has the potential to interfere with the perception of such natural cues. Following a 5-year study on two populations of wild marsupial mammals exposed to different night-time levels of anthropogenic light, we show that light pollution in urban environments masks seasonal changes in ambient light cues, suppressing melatonin levels and delaying births in the tammar wallaby. These results highlight a previously unappreciated relationship linking artificial light at night with induced changes in mammalian reproductive physiology, and the potential for larger-scale impacts at the population level.
Poster
The all-sky night brightness distributions recorded at observing sites with moderate to high levels of light pollution can be efficiently described by polynomial series or relatively low order. This opens the way for estimating these continuous distributions from discrete sets of measurements made in different directions of the sky with photometric detectors of low spatial resolution as, e.g. the Sky Quality Meter, SQM (10º HWHM). Modal estimations of the night sky brightness can be obtained by expanding their equal-area projection maps as a series of orthonormal functions, in particular Zernike polynomials, and fitting the unknown modal coefficients to the measurements provided by the detector. Least squares and minimum variance estimators can be easily developed once the linear functional relationship between the measurements and the actual sky brightness distribution is established.
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In this paper we review new available indicators useful to quantify and monitor light pollution, defined as the alteration of the natural quantity of light in the night environment due to introduction of manmade light. With the introduction of recent radiative transfer methods for the computation of light pollution propagation, several new indicators become available. These indicators represent a primary step in light pollution quantification, beyond the bare evaluation of the night sky brightness, which is an observational effect integrated along the line of sight and thus lacking the three-dimensional information. Highlights • We review new available indicators useful to quantify and monitor light pollution. • These indicators are a primary step in light pollution quantification. • These indicators allow to improve light pollution mapping from a 2D to a 3D grid. • These indicators allow carrying out a tomography of light pollution. • We show an application of this technique to an Italian region.
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The ecological impacts of nighttime light pollution have been a longstanding source of concern, accentuated by realized and projected growth in electrical lighting. As human communities and lighting technologies develop, artificial light increasingly modifies natural light regimes by encroaching on dark refuges in space, in time, and across wavelengths. A wide variety of ecological implications of artificial light have been identified. However, the primary research to date is largely focused on the disruptive influence of nighttime light on higher vertebrates, and while comprehensive reviews have been compiled along taxonomic lines and within specific research domains, the subject is in need of synthesis within a common mechanistic framework. Here we propose such a framework that focuses on the cross-factoring of the ways in which artificial lighting alters natural light regimes (spatially, temporally, and spectrally), and the ways in which light influences biological systems, particularly the distinction between light as a resource and light as an information source. We review the evidence for each of the combinations of this cross-factoring. As artificial lighting alters natural patterns of light in space, time and across wavelengths, natural patterns of resource use and information flows may be disrupted, with downstream effects to the structure and function of ecosystems. This review highlights: (i) the potential influence of nighttime lighting at all levels of biological organisation (from cell to ecosystem); (ii) the significant impact that even low levels of nighttime light pollution can have; and (iii) the existence of major research gaps, particularly in terms of the impacts of light at population and ecosystem levels, identification of intensity thresholds, and the spatial extent of impacts in the vicinity of artificial lights.
Article
There have been major qualitative and quantitative changes in outdoor lighting technology in the last decade. The level of skylight caused by outdoor lighting systems is growing at a very high rate, about 20 percent per year nationwide. In addition, the spectral distribution of man-made light pollution may change in the next decade from one containing a few mercury lines to one containing dozens of lines and a significantly increased continuum level. Light pollution is presently damaging to some astronomical programs, and it is likely to become a major factor limiting progress in the next decade. Suitable sites in the United States for new dark sky observing facilities are very difficult to find. Some of the increase in outdoor illumination is due to the character of national growth and development. Some is due to promotional campaigns, in which questionable arguments involving public safety are presented. There are protective measures which might be adopted by the government; these would significantly aid observational astronomy, without compromising the legitimate outdoor lighting needs of society. Observatories should establish programs to routinely monitor sky brightness as a function of position, wavelength, and time. The astronomical community should establish a mechanism by which such programs can be supported and coordinated.
Article
A model has been constructed to allow calculation of the night-sky brightness caused by a city at its center and outside the city, and at arbitrary zenith distances. A circular city of uniform brightness is assumed, with the total brightness proportional to the population. Molecular scattering and aerosol scattering are included, with the amount of aerosols being an adjustable parameter, and different scale heights being adopted for molecules and aerosols. The reflectivity of the ground and the fraction of light radiated above the horizontal are taken as parameters. Applications are given to several cities, to the general population-distance relations, to brightness-distance relations, and to the city center brightness-population relations.
Article
A model previously constructed for night-sky brightness calculations has been modified to allow for the curvature of the earth. The model has been applied to calculate the brightness at the following observatories: Mount Wilson, Lick, Mount Palomar, Kitt Peak, Sacramento Peak, Mauna Kea, McDonald, San Pedro Martir, Mount Hopkins, Mount Lemmon, Lowell (Mars Hill), Lowell (Anderson Mesa), Fick, Iowa, Van Vleck, David Dunlap, Anglo-Australian, Haute Provence, and Cerro Tololo. Calculations have also been carried out for the following prospective observatory sites: Junipero Serra, Mount Graham, Charleston Peak, Wheeler Peak, Miller Peak, San Benito Mountain, Lowell (Hutch Mountain), Lowell (Saddle Mountain), and South Baldy (New Mexico). The model is extended to calculate magnitudes in the B photometric band.
Article
We present a method to map the artificial sky brightness across large territories in astronomical photometric bands with a resolution of approximately 1 km. This is of use in quantifying the situation regarding night sky pollution, recognizing potential astronomical sites and allowing future monitoring of trends. The artificial sky brightness present in the chosen direction at a given position on the surface of the Earth is obtained by the integration of the contributions produced by every surface area in the surroundings. Each contribution is computed via detailed models for the propagation in the atmosphere of the upward light flux emitted by the area. The light flux is measured with top-of-atmosphere radiometric observations made by the Defense Meteorological Satellite Program (DMSP) Operational Linescan System. We have applied the described method to Europe, obtaining maps of artificial sky brightness in the V and B bands.
Article
The prediction of the magnitude of the faintest star visible through a telescope by a visual observer is a difficult problem in physiology. Many prediction formulas have been advanced over the years, but most do not even consider the magnification used. Here, the prediction algorithm problem is attacked with two complimentary approaches: (1) First, a theoretical algorithm was developed based on physiological data for the sensitivity of the eye. This algorithm also accounts for the transmission of the atmosphere and the telescope, the brightness of the sky, the color of the star, the age of the observer, the aperture, and the magnification. (2) Second, 314 observed values for the limiting magnitude were collected as a test of the formula. It is found that the formula does accurately predict the average observed limiting magnitudes under all conditions.
Article
Of all the functions that define visual performance, the mesopic luminous efficiency function is probably the most complex and hardest to standardise or model. Complexities arise because of the substantial and often rapid visual changes that accompany the transition from scotopic to photopic vision. These are caused not only by the switch from rod to cone photoreceptors, but also by switches between different post-receptoral pathways through which the rod and cone signals are transmitted. In this review, we list several of the complexities of mesopic vision, such as rod-cone interactions, rod saturation, mixed photoreceptor spectral sensitivities, different rod and cone retinal distributions, and the changes in the spatial properties of the visual system as it changes from rod- to cone-mediated. Our main focus, however, is the enormous and often neglected temporal changes that occur in the mesopic range and their effect on luminous efficiency. Even before the transition from rod to cone vision is complete, a transition occurs within the rod system itself from a sluggish, sensitive post-receptoral pathway to a faster, less sensitive pathway. As a consequence of these complexities, any measure of mesopic performance will depend not only on the illumination level, but also on the spectral content of the stimuli used to probe performance, their retinal location, their spatial frequency content, and their temporal frequency content. All these should be considered when attempting to derive (or to apply) a luminous efficiency function for mesopic vision.
Article
There have been major qualitative and quantitative changes in outdoor lighting technology in the last decade. The level of skylight caused by outdoor lighting systems is growing at a very high rate, about 20 percent per year nationwide. In addition, the spectral distribution of man-made light pollution may change in the next decade from one containing a few mercury lines to one containing dozens of lines and a significantly increased continuum level. Light pollution is presently damaging to some astronomical programs, and it is likely to become a major factor limiting progress in the next decade. Suitable sites in the United States for new dark sky observing facilities are very difficult to find. Some of the increase in outdoor illumination is due to the character of national growth and development. Some is due to promotional campaigns, in which questionable arguments involving public safety are presented. There are protective measures which might be adopted by the government; these would significantly aid observational astronomy, without compromising the legitimate outdoor lighting needs of society. Observatories should establish programs to routinely monitor sky brightness as a function of position, wavelength, and time. The astronomical community should establish a mechanism by which such programs can be supported and coordinated.
Article
We present the first World Atlas of the zenith artificial night sky brightness at sea level. Based on radiance calibrated high resolution DMSP satellite data and on accurate modelling of light propagation in the atmosphere, it provides a nearly global picture of how mankind is proceeding to envelope itself in a luminous fog. Comparing the Atlas with the U.S. Department of Energy (DOE) population density database we determined the fraction of population who are living under a sky of given brightness. About two thirds of the World population and 99% of the population in US (excluding Alaska and Hawaii) and EU live in areas where the night sky is above the threshold set for polluted status. Assuming average eye functionality, about one fifth of the World population, more than two thirds of the US population and more than one half of the EU population have already lost naked eye visibility of the Milky Way. Finally, about one tenth of the World population, more than 40% of the US population and one sixth of the EU population no longer view the heavens with the eye adapted to night vision because the sky brightness. Comment: 24 pages, 11 size-reduced PostScript figures, 3 statistical tables, accepted for publication in Monthly Notices of the Royal Astronomical Society, high-resolution original maps will be available soon from http://www.lightpollution.it/dmsp/ as zipped TIFF files
Article
The present work provides the results of the first six years of operation of the systematic night-sky monitoring at ESO-Paranal (Chile). The UBVRI night-sky brightness was estimated on about 10,000 VLT-FORS1 archival images, obtained on more than 650 separate nights, distributed over 6 years and covering the descent from maximum to minimum of sunspot cycle n.23. Additionally, a set of about 1,000 low resolution, optical night-sky spectra have been extracted and analyzed. The unprecedented database discussed in this paper has led to the detection of a clear seasonal variation of the broad band night sky brightness in the VRI passbands, similar to the well known semi-annual oscillation of the NaI D doublet. The spectroscopic data demonstrate that this seasonality is common to all spectral features, with the remarkable exception of the OH rotational-vibrational bands. A clear dependency on the solar activity is detected in all passbands and it is particularly pronounced in the U band, where the sky brightness decreased by about 0.6 mag arcsec-2 from maximum to minimum of solar cycle n.23. No correlation is found between solar activity and the intensity of the NaI D doublet and the OH bands. A strong correlation between the intensity of NI 5200A and [OI]6300,6364A is reported here for the first time. The paper addresses also the determination of the correlation timescales with solar activity and the possible connection with the flux of charged particles emitted by the Sun. Comment: 19 pages, 27 figures, accepted for publication in Astronomy & Astrophysics. Full resolution version at http://www.hq.eso.org/~fpatat/science/skybright/paperIII.pdf
Article
We have produced a data base of V-band and B-band night-sky brightness measurements rather evenly spread out over the course of a whole sunspot cycle from September 1985 to August 1996. Almost all the data were obtained at the 2800-m level of Mauna Kea using the same telescope, same photomultiplier tube, filters, and diaphragm, thus minimizing various sources of systematic error and allowing an estimate of the sources of random error. The yearly V-band averages of observed sky brightness ranged from 21.287 to 21.906 magnitudes per square arc second. The color of the sky is $B-V$ = 0.930 and does not change discernibly over the course of the sunspot cycle. After correcting the V-band data to the zenith, we find that the airglow component varied a factor of 4.5 over the course of the solar cycle. Once the 11-year solar cycle effect is removed from the data, the most significant contribution to the scatter of individual data points appears to be the short term variations on time scales of tens of minutes like those observed by the Whole Earth Telescope project. Comment: 27 pages AAS-style (v 4.0) Latex, 5 figures, to be published in Publications of the Astronomical Society of the Pacific
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