Estimating the relative contribution of streetlights, vehicles and residential lighting to the urban night sky brightness

TL;DR

This paper presents a method to estimate the contributions of streetlights, residential, and vehicle lights to urban night sky brightness by analyzing time-lapse photometry data and transforming brightness measurements into modal coefficients.

Contribution

It introduces a novel approach using modal coefficients and linear least squares fitting to quantify the impact of different artificial light sources on sky brightness.

Findings

Residential light leakage significantly affects sky brightness.

Vehicle lights contribute less to the variability in sky brightness.

The method effectively distinguishes contributions of different light sources.

Abstract

Under stable atmospheric conditions, the zenithal brightness of the urban sky varies throughout the night following the time course of the anthropogenic emissions of light. Different types of artificial light sources (e.g. streetlights, residential, and vehicle lights) present specific time signatures, and this feature makes it possible to estimate the amount of sky brightness contributed by each one of them. Our approach is based on transforming the time representation of the zenithal sky brightness into a modal coefficients one, in terms of the time course signatures of the sources. The modal coefficients, and hence the absolute and relative contributions of each type of source, can be estimated from the measured brightness by means of linear least squares fits. A method for determining the time signatures is described, based on wide-field time-lapse photometry of the urban nightscape. Our preliminary results suggest that artificial light leaking out of the windows of residential buildings may account for a significant share of the time-varying part of the zenithal sky brightness, whilst the contribution of the vehicle lights seems to be significantly smaller.