Measurement of light pollution and sky brightness in a sounding balloon flight: data elaboration through inertial pointing reconstruction.

The MINLU (“Misurazione dell’ INquinamento LUminoso”) payload was successfully launched on July 7th 2021 with a sounding balloon from Tuscany, achieving continuous observation of sky brightness magnitude in Earth atmosphere from ground to stratospheric altitude of 32 km. The operation was the result of a joint effort by the Department of Industrial Engineering (DII) and the Center of Studies and Activities for Space “G.Colombo” of University of Padova which realized the scientific gondola in collaboration with the Space Systems Lab from University of Pisa, that provided its UniPiHAB04 flight platform to carry the system to stratospheric altitude and safely back to ground. MINLU autonomous payload has been designed and tested to provide complete and detailed aerial observations of light pollution sources and sky brightness, with the capability to be integrated either on stratospheric balloons or drones. The implemented architecture includes three cameras with dedicated filters and two commercial Sky Quality Meter (SQM-LE) units, controlled by a Raspberry based Central Data Management Unit performing sensor conditioning, data acquisition, compression and storage; inertial position and attitude information are acquired by on board GPS and IMU units and automatically linked to scientific data. The work will present first results of trajectory and attitude reconstruction along with the elaboration of SQM data during the astronomical night, highlighting the impact of pointing accuracy on the calculation of sky brightness altitude dependant profiles. Since no active attitude control mechanism is present in the payload, light emitting areas on ground may enter in the field of view of SQM, inducing errors in the readings if attitude is not taken into consideration to eliminate such interference from the acquired signal.