Quantifying urban light pollution - A comparison between field measurements and EROS-B imagery

Artificial night lighting and its negative consequences are of interest in the fields of Astronomy, Human Geography, Ecology and Human Health. The majority of studies to date focused on the impacts light pollution has on our ability to view the night sky, as well as on biodiversity, ecosystems and humans. However, in recent years, with the emergence of new high spatial resolution sensors, providing detailed evaluation of night lights at the local level, more attention has been given for estimating and quantifying artificial light within cities. In this study, we evaluate urban night lights within the city of Jerusalem by combining data from two remote sensing tools: ground measurements using Sky Quality Meter (SQM) devices and space-borne measurements using EROS-B night light imagery. In addition, we examined the use of the SQM for evaluating artificial light in different view directions: upwards, downwards and horizontally. Differences in night lights were found between the three SQM view directions, with the brightest values measured in the horizontal direction (8.7-18.9 mag_SQM arcsec^-2, and darkest values in the downwards direction (11.2-19.5 mag_SQM arcsec^-2). The downwards SQM measurements were influenced by surface albedo, the horizontal direction was the most exposed to direct lights from buildings and cars, while in most locations the upwards direction represented skyglow. Using quantile regression we found strong correlations between the SQM and EROS-B brightness values. Statistically significant correlations (R² = 0.53) were found between the upwards and downwards devices to the EROS-B in the 0.95 quantile, as well as between the horizontal device to the EROS-B in the 0.90 quantile (R² = 0.44). In addition to local and external light sources, bright areas on the EROS-B image were associated with areas of low vegetation cover and high albedo. This study provides evidence for the correspondence between field and space-borne measurements of artificial lights and emphasizes the need for better understanding of light pollution at the local level and for taking into account of the three dimensional nature of light pollution.