To evaluate site quality and to develop multi-conjugative adaptive optics systems for future large solar telescopes, characterization of contributions to seeing from heights up to at least 12 km above the telescope is needed. We describe a method for evaluating contributions to seeing from different layers along the line-of-sight to the Sun. The method is based on Shack Hartmann wavefront sensor data recorded over a large field-of-view with solar granulation and uses only measurements of differential image displacements from individual exposures, such that the measurements are not degraded by residual tip-tilt errors. We conclude that the proposed method allows good measurements when Fried's parameter r_0 is larger than about 7.5 cm for the ground layer and that these measurements should provide valuable information for site selection and multi-conjugate development for the future European Solar Telescope. A major limitation is the large field of view presently used for wavefront sensing, leading to uncomfortably large uncertainties in r_0 at 30 km distance.
Astronomical seeing measurements were carried out at Maidanak observatory during the period from August to November 2018 using DIMM (Differential Image Motion Monitor). The median value of seeing for the entire period was determined as 0.54 arcseconds. This value was compared to the seeing data of the period 1996-2002.
Characterisation of atmospheric optical turbulence is crucial for the design and operation of modern ground-based optical telescopes. In particular, the effective application of adaptive optics correction on large and extremely large telescopes relies on a detailed knowledge of the prevailing atmospheric conditions, including the vertical profile of the optical turbulence strength and the atmospheric coherence timescale. The Differential Image Motion Monitor (DIMM) has been employed as a facility seeing monitor at many astronomical observing sites across the world for several decades, providin…
We present a reanalysis of several years of DIMM data at the site of Dome C, Antarctica, to provide measurements of the coherence time $τ_0$. Statistics and seasonal behaviour of $τ_0$ are given at two heights above the ground, 3m and 8m, for the wavelength $λ=500$nm. We found an annual median value of $2.9$ms at the height of 8m. A few measurements could also be obtained at the height of 20m and give a median value of 6ms during the period June--September. For the first time, we provide measurements of $τ_0$ in daytime during the summer, which appears to show the same time dependence as the s…
In this article, we present a detailed analysis of the statistical properties of seeing for the Muztagh-ata site which is the candidate site for hosting future Chinese Large Optical/infrared Telescope (LOT) project. The measurement was obtained with Differential Image Motion Monitor (DIMM) from April 2017 to November 2018 at different heights during different periods. The median seeing at 11 meters and 6 meters are very close but different significantly from that on the ground. We mainly analyzed the seeing at 11 meters monthly and hourly, having found that the best season for observing was fr…
位于智利拉斯坎帕纳斯天文台（LCO）的Cerro Las Campanas被选为巨型麦哲伦望远镜的地点。我们报告自2005年开始对LCO潜在GMT场地进行系统性现场测试调查以来所获得的结果。气象（云量，温度，压力，风和湿度）和DIMM看到的数据已获得在三个潜在的网站，并与相同的数据在网站上采取的麦哲伦6.5米望远镜。此外，测量的自由大气层以上LCO的湍流廓线已收集与MASS/DIMM。此外，我们考虑光度质量，光污染和可降水量（PWV）。LCO，特别是Las Campanas，有黑暗的天空，未来光污染的风险很小或没有，良好的视觉，温和的风，PWV足以在合理的夜晚部分进行中红外天文学，并且总体上有很高的晴朗夜晚。最后，公司Las Campanas符合或超过所有定义的科学要求。
We demonstrate that for data recorded with a solar telescope that uses adaptive optics and/or post-processing to compensate for many low- and high-order aberrations, the RMS granulation contrast is directly proportional to the Strehl ratio calculated from the residual (small-scale) wavefront error. We demonstrate that the wings of the high-order compensated PSF for SST are likely to extend to a radius of not more than about 2 arcsec, consistent with earlier conclusions drawn from straylight compensation of sunspot images. We report on simultaneous measurements of seeing and solar granulation c…
The observations of solar photosphere from the ground encounter significant problems due to the presence of Earth's turbulent atmosphere. Prior to applying image reconstruction techniques, the frames obtained in most favorable atmospheric conditions (so-called lucky frames) have to be carefully selected. However, the estimation of the quality of images containing complex photospheric structures is not a trivial task and the standard routines applied in night-time Lucky Imaging observations are not applicable. In this paper we evaluate 36 methods dedicated for the assessment of image quality wh…
Atmospheric turbulence profiling with the Multistar Turbulence Monitor
School of Physics and Astronomy, Sun Yat-Sen University（中山大学物理学院）；Yunnan Observatory, Chinese Academy of Sciences (CAS)（中国科学院云南天文台）；Department of Physics and Astronomy, University of British Columbia（不列颠哥伦比亚大学物理与天文学系）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；School of Physical Science and Technology, Southwest Jiaotong University（西南交通大学物理科学与技术学院）
The Results of the site selection campaign conducted for the proposed 3.4m optical telescope of the Iranian National Observatory are reported. During the first 3 years, among 33 nominated regions throughout the country, the potential regions were confined to four provinces, namely, Southern Khorasan located in the East, Kerman in the South East and Qom and Esfahan in the central part by examining the long-term meteorological and geographical parameters. Over the following 3 years, after astro-climate considerations and short-term atmospheric seeing measurements using differential image motion …
The telescopes and the infrastructures may alter the local wind environment around the observatory and further affect the observing environment. After the completion of site testing, it is necessary to analyze the wind environment of the entire site and plan the telescope layout to make use of the excellent conditions scientifically and rationally. Taking a typical observatory as an example, the effect of topographical features on wind environment and the mutual interference between telescope enclosures are analyzed by using Computational Fluid Dynamics (CFD) method. The CFD simulations are co…
European Extremely Large Telescope Site Characterization II: High angular resolution parameters
这是一系列致力于欧洲极大望远镜（E-ELT）网站特性的第二篇文章。在这篇文章中，我们提出了高角分辨率观测的E-ELT在设计研究（DS）阶段的现场测试活动中收集的数据所涉及的参数的主要属性。2008年和2009年，在选定的四个地点进行了观测，以庇护未来的E-ELT（根据ELT-DS合同进行表征）：摩洛哥的Aklim山，西班牙的Observatorio del Roque de los Muchachos（ORM），阿根廷的Macón山脉和智利的Cerro Ventarrones。在每个地点采用了同样的技术、仪器和采集程序。在每个站点安装了多孔径闪烁传感器（MASS）和差分图像运动监视器（DIMM）。对每个站点的综合视宁度、自由大气视宁度、边界层视宁度和等晕角进行了全球统计研究，并给出了结果。为了估计其他重要参数，如波前的相干时间和总体参数“相干扩展”，需要风速垂直分布的额外信息。数据来自美国国家海洋和大气管理局（NOAA）的档案。地面风速由自动气象站（AWS）测量。对湍流参数的季节变化、夜间演变和时间稳定性进行了分析。
We present wind and temperature profiles at Dome C measured by balloon born sonds during the polar summer. Data from 197 flights have been processed for 4 campaigns between 2000 and 2004. We show the exceptionnal wind conditions at Dome C, Average ground wind speed is 3.6 m/s. We noticed in mid-november the presence of high altitude strong winds (40 m/s) probably due to the polar vortex which disappear in summer. These winds seem to have no effect on seeing measurements made with a DIMM at the same period. Temperature profiles exhibit a minimum at height 5500 m (over the snow surface) that def…
ALTA project has been active since 2016, providing, at LBT observatory site, forecasts of atmospheric parameters, such as temperature, wind speed and direction, relative humidity and precipitable water vapor, and optical turbulence parameters, such as seeing, wavefront coherence time and isoplanatic angle with the final goal to support nightly the science operation of the LBT. Besides to the forecasts, during the years ALTA has been collecting statistics on the atmospheric conditions which can be used to draw a very accurate characterization of the climatology of the telescope site located on …
