基于虚拟天文馆对全天相机姿态的精确测量

Accurate Measurement of All-sky Camera′s Attitude Based on Virtual Planetarium

全天相机已广泛应用在气象、天文等领域,在监测云量、夜天光、流星时,需要准确掌握相机的姿态参数,特别是在安装和运维中造成的偏差。旨在开发一套基于虚拟天文馆的像场测量方法,通过比较参考恒星的虚拟坐标及其像点的实测坐标,高精度地测量相机的姿态参数。使用中国科学院云南天文台安置于四川无名山观测站的全天相机,分析了2016年至2017年获得的4组全天图像,采集了容量分别约为10、50、200的恒星样本,通过Stellarium虚拟天文馆获得了恒星的地平坐标,对全天相机像场的天顶位置、测者子午线方向等基本参数进行了精确的测量。主要结果为:(1)开发了一种基于虚拟天文馆计算恒星地平坐标功能的测量方法,使姿态测量建立在容量较大的参考恒星上,该方法准确度高,对设备配置的依赖性低,具有较强的可移植性;(2)采用网格法对图像天顶的定位达到了亚像素的精度,有望满足高精度定位监测的需要;(3)全天相机姿态精度的首要指标是光轴的竖直性,光轴偏离天顶对投影的轴对称造成不可忽略的影响;(4)维护作业对圆形像场几何参数的改变甚微,但可能改变指向和旋转角,并需要重新测量;(5)生成了符合制图惯例的可视化产品,为监测数据的深入分析奠定了基础。

All-sky cameras have been widely used in meteorology,astronomy and other fields.In the monitoring of cloud cover,night skylight,meteors and other applications,it is necessary to accurately measure cameras′attitude,especially the deviations caused during installation and maintenance.The purpose of this study is to develop a method to measure camera′s attitude parameters with high precision,by comparing the polar coordinates of reference stars′image points and the stars′horizon coordinates computed by a virtual planetarium,and generate visualization products with errors corrected.Using the all-sky camera developed by the Yunnan Observatories of the Chinese Academy of Sciences and deployed in Sichuan′s Wumingshan observation station,we analyze four sets of all-sky images obtained in October 2016 and June 2017,select star samples with capacities of^10,~50,and^200,obtain their coordinates through the Stellarium planetarium,and accurately acquire the attitude parameters such as the zenith position and rotation angle of the image field.Main results are:(1)We developed a method that is based on virtual planetarium′s function to compute stellar coordinates,and improved the accuracy of the measurement with a large capacity of reference star samples.The method does not rely on the camera′s specs and therefore is transplantable.(2)According to the camera′s attitude on 2016-10-20,its image field′s radius and center coordinates are 0.4289 and(0.7590,0.5048)respectively(in the unit length of the image′s Y direction,the same below);the zenith′s coordinates are:(0.75118±0.00020,0.49572±0.00022);the angle between the zenith and the optic axis is 2.36°;the rotation angle is 152.71±1.58.(3)Maintenance operations have little(≤0.28%)influence upon the geometric parameters of the round-shaped image field,but might cause the optical axis to deviate from the zenith,which will have a non-negligible effect on the axial symmetry of the camera′s projection.Each maintenance will also change the camera′s rotation angle which needs to be re-determined afterwards.(4)Visualization products conforming to industry norms are produced,which will lay the foundation for further study of the surveillance data.