Development of all-sky infrared cloud monitor for the ground based gamma-ray observations

在地基成像大气切伦科夫望远镜的甚高能γ射线观测中，云层对观测计划的制定、观测效率和数据质量有着重要的影响。本研究的目的是研制一台全天空红外相机，以实现对云层的连续监测和客观记录，采用了一种由商用红外相机（光谱响应为8 ~ 14 μm）、凸面镜反射镜和次镜组成的光学系统，以扩大全天空的视角，它是基于日本国家天文台研制并投入实际使用的中红外相机。通过定制的45 m长RS-232电缆，通过PC上的GUI远程控制图像采集。在适当的校准后，我们可以获得清晰的图像，只有通过调整增益与自动偏移模式。晚上，我们可以在显示器上看到肉眼看不到的淡淡的云。此外，通过对数字化数据的一维切片，可以清楚地识别云的位置和相对厚度。通过在沙漠40 ℃以上高温环境下连续9天的运行试验，验证了该系统的有效性，并研制了一台全天空红外测云仪，验证了该系统的有效性，为提高数据质量和有效的调度管理提供了依据。

For the observations of very high energy gamma rays with the ground based imaging atmospheric Cherenkov telescope, clouds significantly affect making observation schedule, observation efficiency and the quality of the data. So the purpose of this research is to develop and fabricate an all-sky infrared camera to monitor clouds constantly and record them objectively.We used an optical system which consists of a combination of a commercially available infrared camera using an uncooled focal plane array whose spectral response is 8 to 14 μm with a convex mirror reflector and a secondary mirror in order to widen the viewing angle to whole sky, which is based on the mid-infrared camera developed and put practical use by National Astronomical Observatory of Japan. An image acquisition is remotely controlled by GUI on the pc through a custom-made 45 m length RS-232 Cable. After an appropriate calibration, we can obtain clear images only by making an adjustment of gain with auto offset mode. In the night, we can see faint clouds on the monitor disply which are invisible to the naked eye. In addition, by one-dimensional slice of digitized data, the position and the relative thickness of clouds are clearly recognized. We confirmed the system works properly during continuous running test of nine days under extremely hot circumstances over 40 degree in the desert.We developed and fabricate an all-sky infrared cloud monitor, and demonstrated the effectiveness of the system, which is expected to provide the improvement of the data quality and effective scheduling management.