Bartolomei Mirco, Olivieri Lorenzo, Bettanini Carlo, Cavazzani Stefano, Fiorentin Pietro
CISAS-Center for Studies and Activities for Space "Giuseppe Colombo", University of Padova, Via Venezia 15, 35131 Padova, Italy.
Department of Industrial Engineering, University of Padova, Via Venezia 1, 35131 Padova, Italy.
Sensors (Basel). 2021 Nov 13;21(22):7544. doi: 10.3390/s21227544.
Sky Quality Meter (SQM) is a commercial instrument based on photometers widely used by amateur astronomers for skyglow measurement from the ground. In the framework of the MINLU project, two SQM-LE units were integrated in an autonomous sensor suite realized and tested at University of Padova for monitoring light pollution from drones or sounding balloons. During the ground tests campaign before airborne measurement, the performance of both SQM units was verified in laboratory using controlled light sources as a reference input; the results showed that both units presented an angular response deviating consistently from the expected performance and that the sensors' field of view was larger than the one declared in the manufacturer's datasheet. This aspect in particular would affect direct skyglow measurements during flight as light sources close to the boundaries of the field of view would not be attenuated but instead detected by the sensors. As a direct consequence, the measurement of low-intensity skyglows at stratospheric altitudes could be affected by high-intensity punctual sources acting as lateral disturbances. A dedicated test campaign was therefore conceived and realized to investigate SQM unit response to light sources in the field of view and identify the true angular response curve; the setup consisted in a controlled rotatory stage moving the unit in front of a fixed diffusive light source. Different test conditions were used to validate the experimental procedure, demonstrating the repeatability of the measurements. This paper presents the experimental campaign and the resulting SQM angular response curve; results indicate for both SQMs a larger than expected field of view and the presence of a double peak in the angular response, which is likely related to a non-perfect alignment of SQMs collimation optics. Furthermore, the wider resulting curves suggest that the contribution of lateral sources is more prominent with respect to the response predicted by the manufacturer. For this reason, the utilization of baffles to restrict SQMs field of view is analyzed to minimize the disturbance of lateral light sources and two different geometries are presented.
天空质量测量仪（SQM）是一种基于光度计的商业仪器，被业余天文学家广泛用于从地面测量天空辉光。在MINLU项目框架内，两个SQM-LE单元被集成到一个自主传感器套件中，该套件在帕多瓦大学实现并进行了测试，用于监测无人机或探空气球产生的光污染。在进行空中测量之前的地面测试活动中，使用受控光源作为参考输入，在实验室中验证了两个SQM单元的性能；结果表明，两个单元的角度响应始终偏离预期性能，并且传感器的视场比制造商数据手册中声明的视场大。这一情况尤其会影响飞行过程中的直接天空辉光测量，因为靠近视场边界的光源不会被衰减，反而会被传感器检测到。因此，会受到作为横向干扰的高强度点状光源的影响。因此，构思并开展了一项专门的测试活动，以研究SQM单元对视场内光源的响应，并确定真实的角度响应曲线；该装置包括一个受控旋转台，将单元在固定的漫射光源前移动。使用不同的测试条件来验证实验程序，证明了测量的可重复性。本文介绍了实验活动以及由此得到的SQM角度响应曲线；结果表明，两个SQM的视场均比预期大，并且角度响应中存在双峰，这可能与SQM准直光学器件的不完全对准有关。此外，得到的更宽曲线表明，横向光源的贡献相对于制造商预测的响应更为突出。因此，分析了使用挡板来限制SQM视场的方法，以尽量减少横向光源的干扰，并给出了两种不同的几何形状。
