Preliminary characterization of a low-light imaging system for ALPHA UAV

Earth’s atmosphere is home to a vast variety of phenomena that have always captured scientists’ interests, especially those that are defined as optical phenomena. The investigation methods are several, starting from ground observations to satellite ones, however, aerial imaging could provide a flexible and versatile solution to perform imaging of multiple target phenomena at once. This is the motivation behind the design and development of ALPHA, a UAV currently in the works at KTH, that has the aim to image the most significant phenomena. In this work, ALPHA’s payload main requirements have been defined, following two main topics of research: the study of the target phenomena, and the technical requirements of the imaging system in terms of sensors, lenses, and filter characteristics. The phenomena that have been investigated are auroras, nightglow, noctilucent clouds, sprites and jets, and for each of them the main emission lines, or bands, have been selected, highlighting the processes that cause them, as well as their intensity and lifetime. Moreover, the sensors, lenses and filter characteristics have been analysed, focusing in particular on sensor type and size, pixel size, resolution, weight and power requirement of the camera, as well as the f-number and field of view of the lenses.
In addition to this a method to perform a preliminary comparison of the cameras has been presented, using as the main parameter the SNR, calculated taking into account the noise sources of each sensor and the average column volume emission rate in Rayleigh of the selected emission lines. This method provides a quantitative parameter to help choose from any camera on the market, as well as highlighting its behaviour with different exposure times.