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

在地面成像大气切伦科夫望远镜进行甚高能伽马射线观测时，云层对观测计划的制定、观测效率和数据质量有显著影响。因此，本课题的研究目的是研制一种全天候红外摄像机，实现对云的持续监测和客观记录。为了扩大对整个天空的观测角度，我们在日本国家天文台研制并实际应用的中红外相机的基础上，采用了一种将光谱响应为8 ~ 14 μm的非冷却焦平面阵列红外相机与凸面镜反射镜和副反射镜组合而成的光学系统。通过定制的45米长的RS-232电缆，在pc上通过GUI远程控制图像采集。经过适当的校准后，我们只需要用自动偏移模式调整增益就可以获得清晰的图像。在夜晚，我们可以在显示器上看到肉眼看不见的微弱的云。此外，通过数字化数据的一维切片，可以清晰地识别云的位置和相对厚度。在40度以上的沙漠高温环境下，经过9天的连续运行测试，系统运行正常。研制了一种全天候红外云监测仪，并验证了该系统的有效性，有望为提高数据质量和有效的调度管理提供帮助。

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.