The nature of the diffuse light near cities detected in nighttime satellite imagery

TL;DR

This study demonstrates that the diffuse glow around cities in nighttime satellite images is caused by atmospheric scattering of artificial light, not sensor error, enabling potential monitoring of city light pollution over time.

Contribution

The paper provides evidence that diffuse glow near cities is real atmospheric scattering, challenging the assumption of sensor error and opening avenues for monitoring artificial skyglow.

Findings

Diffuse glow correlates with city brightness across sensors.

Atmospheric scattering causes the observed glow, not sensor artifacts.

Potential for satellite-based monitoring of artificial skyglow.

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 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.