使用MOAO探路者CANARY天空数据的威廉赫歇尔望远镜场地特征
William Herschel Telescope site characterization using the MOAO pathfinder CANARY on-sky data
摘要：
Canary是多目标自适应光学（MOAO）的未来MOAO辅助积分场单元（IFU）的探路者，建议用于极大望远镜（ELT）。MOAO概念依赖于使用沿着不同视线的多次测量来断层重建湍流。层析成像需要了解统计湍流参数，通常使用专用的剖面技术从系统遥测中恢复。为了使用MOAO路径探测器Canary进行演示，该识别是通过学习和应用（L&A）算法进行的，该算法包括根据相关参数对WFS测量的协方差矩阵进行模型拟合：$C_n^2(h)$轮廓、外尺度轮廓和系统误配准。我们探讨了这种算法的升级，学习3步骤（L3 S）的方法，它允许一个分离的高度层从地面的识别，以减轻缺乏收敛所需的经验协方差矩阵，从而减少所需的数据时间序列的长度达到给定的精度。对于标称观测条件，L3 S可以达到相同水平的层析成像误差，使用比L&A方法少五倍的数据帧。L3 S技术已被应用于大量的Canary数据来表征William Herschel望远镜（WHT）上方的湍流。这些数据是在2013年9月13日、15日、16日、17日和18日获得的，我们发现总视宁度/外尺度/风速为0.67”/8.9m/3.07m/s，1.5 km以下为0.552”/9.2m/2.89m/s，1.5 - 20 km之间为0.263”/10.3m/5.22m/s。我们还确定了20 km以上的高海拔层，它被Canary的层析重建所遗漏，具有0.187”的中位视见度，并且出现了16%的观测时间。
英文摘要：
Canary is the Multi-Object Adaptive Optics (MOAO) pathfinder for the future MOAO-assisted Integral-Field Units (IFU) proposed for Extremely Large Telescopes (ELT). The MOAO concept relies on tomographically reconstructing the turbulence using multiple measurements along different lines of sight. Tomography requires the knowledge of the statistical turbulence parameters, commonly recovered from the system telemetry using a dedicated profiling technique. For demonstration purposes with the MOAO pathfinder Canary , this identification is performed thanks to the Learn & Apply (L&A) algorithm, that consists in model- fitting the covariance matrix of WFS measurements dependent on relevant parameters: $C_n^2(h)$ profile, outer scale profile and system mis-registration. We explore an upgrade of this algorithm, the Learn 3 Steps (L3S) approach, that allows one to dissociate the identification of the altitude layers from the ground in order to mitigate the lack of convergence of the required empirical covariance matrices therefore reducing the required length of data time-series for reaching a given accuracy. For nominal observation conditions, the L3S can reach the same level of tomographic error in using five times less data frames than the L&A approach. The L3S technique has been applied over a large amount of Canary data to characterize the turbu- lence above the William Herschel Telescope (WHT). These data have been acquired the 13th, 15th, 16th, 17th and 18th September 2013 and we find 0.67"/8.9m/3.07m/s of total seeing/outer scale/wind-speed, with 0.552"/9.2m/2.89m/s below 1.5 km and 0.263"/10.3m/5.22m/s between 1.5 and 20 km. We have also de- termined the high altitude layers above 20 km, missed by the tomographic reconstruction on Canary , have a median seeing of 0.187" and have occurred 16% of observation time.
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