High correlation but high scale-dependent variance between satellite measured night lights and terrestrial exposure

Abstract

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 satellitemeasured 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.

A Case for a New Satellite Mission for Remote Sensing of Night Lights

“…For example, recent research has demonstrated the influence of light at night at a coarse scale on mountain lion predation on mule deer [45]. Because irradiance from ALAN can vary orders of magnitude within several hundred meters [46], higherresolution data are needed to sort the influence of ALAN on many existing datasets containing ecological information. For example, the National Park Service has an extensive species monitoring program, the data from which are ideally suited for queries on the effects of ALAN on species distribution, co-occurrence, and abundance.…”

Reviewing the Role of Outdoor Lighting in Achieving Sustainable Development Goals

“…A valid option to quantify light pollution can be the merge of ground level measurements with aerial ones. In this context, some studies have identified a reasonable correlation for light imagery between ground and satellite measurements [162,163]. Another path to quantify light pollution can be found in analytical modelling methods of sky glow.…”

11 Pressing Research Questions on How Light Pollution Affects Biodiversity

“…Night-time satellite data are limited in spatial, spectral and temporal resolution, but color imaging from the international space station ISS, airborne measurements, and particularly UAVs have the potential to fill the existing gaps in ALAN related biodiversity research (Bouroussis and Topalis, 2020;Levin et al, 2020;Sánchez de Miguel et al, 2021). A key component to improving the utility of these data would be research efforts that can translate what remotely sensed values could represent for conditions at ground level, where first steps have been taken but uncertainties remain high (Simons et al, 2020). Furthermore, there is an urgent need for stand-alone satellite missions focused on understanding light pollution and its effects on biodiversity (Barentine et al, 2021).…”