Abstract
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 light source. Here we show that the effect seen on the DMSP/OLS, SNPP/VIIRS-DNB and ISS is not only 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.
Highlights
A diffuse glow of light surrounding cities, such as that seen in Fig. 1, was noted by the Earth Observation Group (EOG) who were at the National Oceanic and Atmospheric Administration from their earliest publications of nighttime light data sets (e.g1,2.)
We used measurements taken from space by the Defence Meteorological Satellite Program Operational Linescan System (DMSP), and data with higher resolution and sensitivity from the Suomi North Polar Partnership (SNPP) Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band (DNB) and astronaut photographs from the International Space Station (ISS)[23,24,25,26]
There is a strong correlation between the zenith night sky radiance data from the Universidad Complutense de Madrid (UCM) sky brightness survey and the space-based datasets with both low (Fig. 3) and high resolution (Fig. 4)
Summary
A diffuse glow of light surrounding cities, such as that seen in Fig. 1, was noted by the Earth Observation Group (EOG) who were at the National Oceanic and Atmospheric Administration from their earliest publications of nighttime light data sets (e.g1,2.). Newer satellite data are no longer restricted by the saturation problems and low spatial resolution of DMSP data, but still contain the glow near cities (Fig. 1). This strongly suggests that the glow is not an instrumental effect, but rather real light being detected by the instruments. The azimuthal symmetry of Mie scattering implies that a similar amount of large angle scatter would occur in both the upward and downward directions Taken together, these facts imply that if atmospheric scattering is the cause of the glow around cities, one must expect a fairly strong relationship between skyglow observed from the ground and the glow in satellite imagery. In the case of the satellite data, we only considered areas with sky brightness (SB) darker than 18.5 magSQM/ arcsec[2]
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