Correia Carlos, Véran Jean-Pierre, Herriot Glen
National Research Council, Herzberg Institute of Astrophysics, Victoria, British Columbia, Canada.
J Opt Soc Am A Opt Image Sci Vis. 2012 Mar 1;29(3):185-94. doi: 10.1364/JOSAA.29.000185.
Vibration suppression in astronomical adaptive optics (AO) systems has gathered great attention in the context of next-generation instrumentation for current telescopes and future Extremely Large Telescopes. Laser tomographic AO systems require natural guide stars to measure the low-order modes such as tip-tilt (TT) and TT-anisoplanatism. To increase the sky coverage, the guide stars are often faint, thus requiring lower temporal sampling frequencies to work on a more favorable signal-to-noise regime. Such sampling frequencies can be of the order of, or even lower than, the range of frequencies where vibrations are likely to appear. Ideally, vibrations affecting the low-order modes could be corrected at the higher laser loop frame rate using an upsampling procedure. This paper compares the most relevant solutions proposed hitherto to a novel multirate algorithm using the linear-quadratic-Gaussian (LQG) approach capable of upsampling the correction to further reduce the impact of vibrations. Results from numerical Monte Carlo simulations span a large range of parameters from pure sinusoids to relatively broad peak vibrations, covering the likely-to-be signals in a realistic AO system. The improvement is shown at sampling frequencies from 20 to 800 Hz, including below the vibration itself, in the example of 29.5 Hz on a Thirty Meter Telescope-like scenario. The multirate LQG ensures the least residual for both faint and bright stars for all the peak widths considered based on telemetry from the Keck Observatory.
在当前望远镜和未来极大望远镜的下一代仪器背景下，天文自适应光学（AO）系统中的振动抑制受到了广泛关注。激光层析AO系统需要自然导星来测量诸如倾斜（TT）和TT非等晕性等低阶模式。为了增加天空覆盖范围，导星通常很暗，因此需要较低的时间采样频率，以便在更有利的信噪比条件下工作。这样的采样频率可能处于，甚至低于振动可能出现的频率范围。理想情况下，影响低阶模式的振动可以使用上采样程序在更高的激光回路帧率下进行校正。本文将迄今为止提出的最相关解决方案与一种使用线性二次高斯（LQG）方法的新型多速率算法进行了比较，该算法能够对校正进行上采样，以进一步降低振动的影响。数值蒙特卡罗模拟结果涵盖了从纯正弦波到相对较宽峰值振动的大范围参数，涵盖了实际AO系统中可能出现的信号。在20至800Hz的采样频率下，包括低于振动频率本身的情况（如在类似三十米望远镜的场景中29.5Hz的情况）展示了改进效果。基于凯克天文台的遥测数据，多速率LQG对于所有考虑的峰值宽度，都能确保暗星和亮星的残余量最小。
