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Register a new userLight pollution offshore: zenithal sky glow measurements in the Mediterranean coastal waters
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Light pollution is a worldwide phenomenon whose consequences for the natural environment and the human health are being intensively studied nowadays. Most published studies address issues related to light pollution inland. Coastal waters, however, are spaces of high environmental interest, due to their biodiversity richness and their economical significance. The elevated population density in coastal regions is accompanied by correspondingly large emissions of artificial light at night, whose role as an environmental stressor is increasingly being recognized. (...) At the same time, the marine surface environment provides a stage free from obstacles for measuring the dependence of the skyglow on the distance to the light polluting sources, and validating (or rejecting) atmospheric light propagation models. In this work we present a proof-of-concept of a gimbal measurement system that can be used for zenithal skyglow measurements on board both small boats and large vessels under actual navigation conditions. We report the results obtained in the summer of 2016 along two measurement routes in the Mediterranean waters offshore Barcelona, travelling 9 and 31.7 km away from the coast. The atmospheric conditions in both routes were different from the ones assumed for the calculation of recently published models of the anthropogenic sky brightness. They were closer in the first route, whose results approach better the theoretical predictions. The results obtained in the second route, conducted under a clearer atmosphere, showed systematic differences that can be traced back to two expected phenomena, which are a consequence of the smaller aerosol content: the reduction of the anthropogenic sky glow at short distances from the sources, and the slower decay rate of brightness with distance, which gives rise to a relative excess of brightness at large distances from the coastline.
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We describe the level of light pollution in and around Kirksville, Missouri and at Anderson Mesa near Flagstaff, Arizona by measuring the sky brightness using Unihedron sky quality meters. We report that, on average, the Anderson Mesa site is approximately 1.3 mag/arcsec$^2$ darker than the Truman State Observatory site, and approximately 2.5 mag/arcsec$^2$ darker than the roof of the science building at Truman State University in Kirksville. We also show that at the Truman observatory site, the North and East skies have significantly high sky brightness (by about 1 mag/arcsec$^2$) as compared to the South and West skies. Similarly, the sky brightness varies significantly with azimuth on the top of the science building at Truman State -- the west direction being as much as 3 mag/arcsec$^2$ brighter than the south direction. The sky brightness at Anderson Mesa is much more uniform, varying by less than 0.4 mag/arcsec$^2$ at most along the azimuthal direction. Finally, we describe the steps we are taking in the Kirksville area to mitigate the nuisance of light pollution by installing fully shielded outdoor light fixtures and improved outdoor lights on Truman State Universitys campus.
Light pollution is actively destroying our ability to see the stars. Many Indigenous traditions and knowledge systems around the world are based on the stars, and the peoples ability to observe and interpret stellar positions and properties is of critical importance for daily life and cultural continuity. The erasure of the night sky acts to erase Indigenous connection to the stars, acting as a form of ongoing cultural and ecological genocide. Efforts to reduce, minimise, or eliminate light pollution are being achieved with varying degrees of success, but urban expansion, poor lighting design, and the increased use of blue-light emitting LEDs as a cost-effective solution is worsening problems related to human health, wildlife, and astronomical heritage for the benefit of capitalistic economic growth. We provide a brief overview of the issue, illustrating some of the important connections that the Aboriginal and Torres Strait Islander people of Australia maintain with the stars, as well as the impact growing light pollution has on this ancient knowledge. We propose a transdisciplinary approach to solving these issues, using a foundation based on Indigenous philosophies and decolonising methodologies.
We study the vertical dispersion and distribution of negatively buoyant rigid microplastics within a realistic circulation model of the Mediterranean sea. We first propose an equation describing their idealized dynamics. In that framework, we evaluate the importance of some relevant physical effects: inertia, Coriolis force, small-scale turbulence and variable seawater density, and bound the relative error of simplifying the dynamics to a constant sinking velocity added to a large-scale velocity field. We then calculate the amount and vertical distribution of microplastic particles on the water column of the open ocean if their release from the sea surface is continuous at rates compatible with observations in the Mediterranean. The vertical distribution is found to be almost uniform with depth for the majority of our parameter range. Transient distributions from flash releases reveal a non-Gaussian character of the dispersion and various diffusion laws, both normal and anomalous. The origin of these behaviors is explored in terms of horizontal and vertical flow organization.
Several light pollution indicators are commonly used to monitor the effects of the transition from outdoor lighting systems based on traditional gas-discharge lamps to solid-state light sources. In this work we analyze a subset of these indicators, including the artificial zenithal night sky brightness in the visual photopic and scotopic bands, the brightness in the specific photometric band of the widely used Sky Quality Meter (SQM), and the top-of-atmosphere radiance detected by the VIIRS-DNB radiometer onboard the satellite Suomi-NPP. Using a single-scattering approximation in a layered atmosphere we quantitatively show that, depending on the transition scenarios, these indicators may show different, even opposite behaviors. This is mainly due to the combined effects of the changes in the sources spectra and angular radiation patterns, the wavelength-dependent atmospheric propagation processes and the differences in the detector spectral sensitivity bands. It is suggested that the possible presence of this differential behavior should be taken into account when evaluating light pollution indicator datasets for assessing the outcomes of public policy decisions regarding the upgrading of outdoor lighting systems.
Diffuse glow has been observed around brightly lit cities in nighttime satellite imagery since at least the first publication of large scale maps in the late 1990s. In the literature, this has often been assumed to be an error related to the sensor, and referred to as blooming, presumably in relation to the effect that can occur when using a CCD to photograph a bright source. Here we show that the effect is not instrumental, but in fact represents a real detection of light scattered by the atmosphere. Data from the Universidad Complutense Madrid sky brightness survey are compared to nighttime imagery from multiple sensors with differing spatial resolutions, and found to be strongly correlated. These results suggest that it should be possible for a future space-based imaging radiometer to monitor changes in the diffuse artificial skyglow of cities.
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