Drone photometry enables characterization of upward emission patterns of light-pollution sources

The angular distribution of radiant intensity of an artificial light source (hereafter city emission function; CEF) is the key input to all light pollution propagation models. Yet observational data remain unavailable for the vast majority of urban areas worldwide, forcing sky-glow modelling to rely on generic analytical approximations for decades. Here we present a method that makes systematic characterization of the emission function genuinely practical. Zenith night-sky brightness is measured at ground level and at a fixed altitude using a drone-mounted photometer. The difference between the two signals directly encodes the upward emission geometry of the source. The retrieval of the CEF is simple because it relies on the single-scattering approximation at short distances from the light source and is independent of atmospheric properties above the drone’s flight altitude. Numerical experiments confirm applicability across a wide range of aerosol conditions, with drone altitudes above 220 m sufficient even under the most challenging scattering scenarios. The method opens a realistic pathway toward routine monitoring of light-pollution emission patterns for urban areas where no such data exist.