Flight test of an autonomous payload for measuring sky brightness and ground light pollution using a stratospheric sounding balloon

Abstract

Light pollution is recognized as an increasingly important issue not only for astronomical observations but also for the preservation of ecosystem and the quality of human life. Emission from ground sources is currently mapped using satellite images aided by local ground observations but information has limited resolution in space and time; especially now that blue “cold” LEDs, which are poorly detected from space, are being widely used for illumination, data need to be integrated with measurement from autonomous systems flying at lower altitude.MINLU (“Misurazione dell’ INquinamento LUminoso”) autonomous payload was designed and tested to provide complete and detailed aerial observations of all light pollution sources and monitor sky brightness with the capability to be integrated on stratospheric balloons, tethered balloons or drones. The payload's architecture includes three downward looking cameras with dedicated filters and two commercial Sky Quality Meter (SQM-LE) units, one pointing in horizontal direction and the other monitoring the zenith sky. The system can achieve a ground sample distance of 3 cm when integrated on drones flying at 200 m altitude, going up to 8 m at altitudes above 30 km in the use with balloons; this considerably improves the information provided by satellite images showing a ground resolution around 800 m.The payload was successfully launched with a sounding balloon from Tuscany on July 8th, 2021 during the astronomical night window, achieving the first continuous observation of sky brightness magnitude in Earth atmosphere from ground to stratospheric altitudes. In parallel, images of on-board cameras have been used to quantify ground emission in terms of luminous intensity and power density and allowed to track sources causing the artificial luminance of the sky.