Launch of a sounding balloon for horizontal and vertical modeling of the ALAN propagation in the atmosphere

Abstract The propagation of light radiation in the atmosphere is a topic that needs to be properly analyzed to mitigate its negative influence on astronomical observation. This work describes a novel approach for evaluating atmospheric propagation of artificial light at night emphasizing (ALAN) the dependence on altitude and aerosols; it is based on an innovative experiment using a sounding balloon equipped with two sky quality meters (SQM): one vertically pointed at 30○ (SQM-V) and the other horizontally at 90○ (SQM-H) from the zenith. The system was launched during astronomical night condition from an area of the Italian Apennines with low ground light emission and crossed the Tuscan sky, observing the vertical and horizontal ALAN propagation. The data analysis of the two SQMs and their georeferentiation through altitude and trajectory reconstruction allows to model the propagation of light in the experiment field of view from few hundred meters up to an altitude of about 30 km. In this work main focus is given to the tropospheric part of atmosphere up to 12500 meters: the processed data is used to validate a theoretical model taking into account the altitude, the course of the balloon, the atmospheric composition and the population of the cities overflown by the balloon obtaining a correlation of 0.85 with the SQM-H and 0.91 with the SQM-V. The magnitude values close to 21.5 mag arcsec−2 measured by the SQM-V at 2000 meters are an important experimental result for evaluating the influence of the aerosols and the altitude on the ALAN propagation.