丽江天文观测站全天相机介绍

An Introduction to the All-Sky Camera at the YNAO Lijiang Astronomical Station

全天相机作为一个对天文观测台站全天云量信息进行监视的工具,对天文观测的正常进行发挥着重要的作用,目前世界上主要天文台均配备有全天相机,为了满足对全天云量信息进行实时监视的需求,丽江天文观测站正式安装架设了一套全天相机系统。从硬件安装架设、软件调试到实际测试等方面,详细介绍了全天相机系统的设计方案以及遇到的问题,讨论了对问题的解决措施,重点介绍了根据天光亮度数值调整相机曝光时间的方法,这也是主要创新与特色之处。

An all-sky camera serves as a rather important tool for monitoring cloud distributions over an astronomical observation site. An all-sky camera can improve weather monitoring for astronomical observations, including outdoor observations in site selection. Major observatories in the world now have all-sky cameras. In order to meet the requirements on real-time monitoring of clouds for Yunnan Observatories, we have installed an all-sky camera system at the Lijiang astronomical station. In this paper we describe details of the design and implementation of the all-sky camera system. These include issues of installing hardware, debugging software, and practical tests. We list solutions of these issues. A particular issue is that sky-brightness values can vary dramatically with levels of cloud coverage. This makes it difficult to manually set proper exposures in using the camera. We have found a method to automatically adjust camera exposures according to sky-brightness values. The method sets camera exposures to decrease with sky-brightness values. With exposures correctly set with this method in either day or night, the camera can obtain high-quality all-sky images. This method is also the most innovative and characteristic part of our work with the all-sky camera.