Detecting changes in anthropogenic light emissions: limits due to atmospheric variability

TL;DR

This paper examines how atmospheric variability, especially in molecular and aerosol optical depths, limits our ability to detect small annual changes in anthropogenic light emissions using ground and satellite measurements.

Contribution

It provides an analysis of atmospheric fluctuations' impact on detecting light emission changes and highlights the need for controlling or correcting these atmospheric parameters.

Findings

Atmospheric variability sets a lower detection limit for light emission changes.

Detecting ~1% annual changes requires controlling atmospheric optical depth fluctuations.

Inter-annual atmospheric variability must be carefully managed for reliable detection.

Abstract

Monitoring the evolution of the anthropogenic light emissions is a priority task in light pollution research. Among the complementary approaches that can be adopted to achieve this goal stand out those based on measuring the direct radiance of the sources at ground level or from low Earth orbit satellites, and on measuring the scattered radiance (known as artificial night sky brightness or skyglow) using networks of ground-based sensors. The terrestrial atmosphere is a variable medium interposed between the sources and the measuring instruments, and the fluctuation of its optical parameters sets a lower limit for the actual source emission changes that can be confidently detected. In this paper we analyze the effect of the fluctuations of the molecular and aerosol optical depths. It is shown that for reliably detecting changes in the anthropogenic light emissions of order ~1% per year, the inter-annual variability of the annual means of these atmospheric parameters in the measurement datasets must be carefully controlled or efficiently corrected for.