Ground-based solar observations are severely affected by Earth's turbulent atmosphere. As a consequence, observed image quality and prevailing seeing conditions are closely related. Partial correction of image degradation is nowadays provided in real-time by adaptive optics (AO) systems. In this study, different metrics of image quality are compared with parameters characterizing the prevailing seeing conditions, i.e., Median Filter Gradient Similarity (MFGS), Median Filter Laplacian Similarity (MFLS), Helmli-Scherer mean, granular rms-contrast, differential image motion, and Fried-parameter r0. The quiet-Sun observations at disk center were carried out at the Vacuum Tower Telescope (VTT), Observatorio del Teide (OT), Izana, Tenerife, Spain. In July and August 2016, time-series of short-exposure images were recorded with the High-resolution Fast Imager (HiFI) at various wavelengths in the visible and near-infrared parts of the spectrum. Correlation analysis yields the wavelength dependence of the image quality metrics and seeing parameters, and Uniform Manifold Approximation and Projection (UMAP) is employed to characterize the seeing on a particular observing day. In addition, the image quality metrics and seeing parameters are used to determine the field-dependence of the correction provided by the AO system. Management of high-resolution imaging data from large-aperture, ground-based telescopes demands reliable image quality metrics and meaningful characterization of prevailing seeing conditions and AO performance. The present study offers guidance how to retrieve such information ex post facto.
Real-time seeing estimation at the focus of a telescope is nowadays strongly emphasized as this knowledge virtually drives the dimensioning of adaptive optics systems and instrument operational aspects. In this context we study the interest of using active optics Shack-Hartmann (AOSH) sensor images to provide accurate estimate of the seeing. The AOSH practically delivers long exposure spot PSFs -- at the critical location of the telescope focus -- being directly related to the atmospheric seeing in the line of sight. Although AOSH sensors are not specified to measure spot sizes but slopes, we …
HIRES, a high resolution spectrometer, is one of the first five instruments foreseen in the ESO roadmap for the E-ELT. This spectrograph should ideally provide full spectral coverage from the UV limit to 2.5 microns, with a resolving power from R$\sim$10,000 to R$\sim$100,000. At visual/blue wavelengths, where the adaptive optics (AO) cannot provide an efficient light-concentration, HIRES will necessarily be a bulky, seeing-limited instrument. The fundamental question, which we address in this paper, is whether the same approach should be adopted in the near-infrared range, or HIRES should onl…
Real-time seeing and outer scale estimation at the location of the focus of a telescope is fundamental for the adaptive optics systems dimensioning and performance prediction, as well as for the operational aspects of instruments. This study attempts to take advantage of multiwavelength long exposure images to instantaneously and simultaneously derive the turbulence outer scale and seeing from the full-width at half-maximum (FWHM) of seeing-limited images taken at the focus of a telescope. These atmospheric parameters are commonly measured in most observatories by different methods located awa…
The exoplanetary science through direct imaging and spectroscopy will largely expand with the forthcoming development of new instruments at the VLT (SPHERE), Gemini (GPI), Subaru (HiCIAO), and Palomar (Project 1640) observatories. All these ground-based adaptive optics instruments combine extremely high performance adaptive optics (XAO) systems correcting for the atmospheric turbulence with advanced starlight-cancellation techniques such as coronagraphy to deliver contrast ratios of about 10-6 to 10-7. While the past fifteen years have seen intensive research and the development of high-contra…
Ground-based direct imaging surveys like the Gemini Planet Imager Exoplanet Survey (GPIES) rely on Adaptive Optics (AO) systems to image and characterize exoplanets that are up to a million times fainter than their host stars. One factor that can reduce AO performance is turbulence induced by temperature differences in the instrument's immediate surroundings (e.g.: "dome seeing" or "mirror seeing"). In this analysis we use science observations, AO telemetry, and environmental data from September 2014 to February 2017 of the GPIES campaign to quantify the effects of "mirror seeing" on the perfo…
Seeing-limited resolution in large telescopes working over wide wavelength range depends substantially on the turbulence outer scale and cannot be adequately described by one "seeing" value. We attempt to clarify frequent confusions on this matter. We study the effects of finite turbulence outer scale and partial adaptive corrections by means of analytical calculations and numerical simulations. If a von Karman turbulence model is adopted, a simple approximate formula captures the dependence of atmospheric long-exposure resolution on the outer scale over the entire practically interesting rang…
Adaptive Optics (AO) is an innovative technique that substantially improves the optical performance of ground-based telescopes. The SOAR Adaptive Module (SAM) is a laser-assisted AO instrument, designed to compensate ground-layer atmospheric turbulence in near-IR and visible wavelengths over a large Field of View. Here we detail our proposal to upgrade SAM, dubbed SAMplus, that is focused on enhancing its performance in visible wavelengths and increasing the instrument reliability. As an illustration, for a seeing of 0.62 arcsec at 500 nm and a typical turbulence profile, current SAM improves …
Adaptive optics laser guide star systems perform atmospheric correction of stellar wavefronts in two parts: stellar tip-tilt and high-spatial-order laser-correction. The requirement of a sufficiently bright guide star in the field-of-view to correct tip-tilt limits sky coverage. Here we show an improvement to effective seeing without the need for nearby bright stars, enabling full sky coverage by performing only laser-assisted wavefront correction. We used Robo-AO, the first robotic AO system, to comprehensively demonstrate this laser-only correction. We analyze observations from four years of…
Seeing at Timau National Observatory Based on ERA5 Dataset
Research Centre for Space, National Research and Innovation Agency（国家研究与创新署空间研究中心）；Research School of Astronomy & Astrophysics, Australian National University（澳大利亚国立大学天文与天体物理研究学院）；Astronomy Research Group, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung（万隆理工学院数学与自然科学学院天文学研究组）；Timau National Observatory, National Research and Innovation Agency（国家研究与创新署蒂马乌国家天文台）
The Shack-Hartman wavefront sensor designed for final acceptance of 2.5m SAI telescope allows to measure the shape of the wavefront on exit pupil of the telescope using a bright star. The reference laser source on wavelength 532 nm is used for measurements. During testing the device at different telescopes it was found out what it's probable to estimate some properties of air streams in the dome. Such estimations have been made for three domes: 1.5 m AZT-22 and 1.0 m Zeiss telescope of Maidanak Observatory, Uzbekistan and for 2.6 m telescope ZTSh of Crimean observatory, Ukraine. The following …
Atmospheric optical turbulence seriously limits the performance of high angular resolution instruments. An 8-night campaign of measurements was carried out at the LAMOST site in 2011, to characterize the optical turbulence. Two instruments were set up during the campaign: a Differential Image Motion Monitor (DIMM) used to measure the total atmospheric seeing, and a Single Star Scidar (SSS) to measure the vertical profiles of the turbulence C_n^2(h) and the horizontal wind velocity V(h). The optical turbulence parameters are also calculated with the Weather Research and Forecasting (WRF) model …
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…
Accurate measurement of polarization in spectral lines is important for the reliable inference of magnetic fields on the Sun. For ground based observations, polarimetric precision is severely limited by the presence of Earth's atmosphere. Atmospheric turbulence (seeing) produces signal fluctuations which combined with the non-simultaneous nature of the measurement process cause intermixing of the Stokes parameters known as seeing induced polarization cross-talk. Previous analysis of this effect (Judge et al., 2004) suggests that cross-talk is reduced not only with increase in modulation freque…
We present results from the first year of a campaign to characterize and monitor the optical turbulence profile at the SAAO Sutherland observing station in South Africa. A MASS-DIMM (MultiAperture Scintillation Sensor - Differential Image Motion Monitor) was commissioned in March 2010 to provide continuous monitoring of the seeing conditions. Over the first month of the campaign, a SLODAR (SLOpe Detection And Ranging) from Durham University was also installed allowing an independent verification of the performance of the MASS-DIMM device. After the first year of data collection, the overall me…
We report results of a two-year campaign of measurements, during arctic winter darkness, of optical turbulence in the atmospheric boundary-layer above the Polar Environment Atmospheric Laboratory in northern Ellesmere Island (latitude +80 deg N). The data reveal that the ground-layer turbulence in the Arctic is often quite weak, even at the comparatively-low 610 m altitude of this site. The median and 25th percentile ground-layer seeing, at a height of 20 m, are found to be 0.57 and 0.25 arcsec, respectively. When combined with a free-atmosphere component of 0.30 arcsec, the median and 25th pe…
The high-speed variability of the local water vapor content in the Earth atmosphere is a significant contributor to ground-based wavefront quality throughout the infrared domain. Unlike dry air, water vapor is highly chromatic, especially in the mid-infrared. This means that adaptive optics correction in the visible or near-infrared domain does not necessarily ensure a high wavefront quality at longer wavelengths. Here, we use literature measurements of water vapor seeing, and more recent infrared interferometric data from the Very Large Telescope Interferometer (VLTI), to evaluate the wavefro…
Using an observational derived model optical turbulence profile (model-OTP) we have investigated the performance of Adaptive Optics (AO) at Siding Spring Observatory (SSO), Australia. The simulations cover the performance for AO techniques of single conjugate adaptive optics (SCAO), multi-conjugate adaptive optics (MCAO) and ground-layer adaptive optics (GLAO). The simulation results presented in this paper predict the performance of these AO techniques as applied to the Australian National University (ANU) 2.3 m and Anglo-Australian Telescope (AAT) 3.9 m telescopes for astronomical wavelength…
Atmospheric turbulence is the one of the major limiting factors for ground-based astronomical observations. In this paper, the problem of short-term forecasting seeing is discussed. The real data that were obtained by atmospheric optical turbulence (OT) measurements above Mount Shatdzhatmaz in 2007--2013 have been analysed. Linear auto-regressive integrated moving average (ARIMA) models are used for the forecasting. A new procedure for forecasting the image characteristics of direct astronomical observations (central image intensity, full width at half maximum, radius encircling 80% of the ene…
The image quality budget of many telescopes can have substantial contributions from local seeing, both``mirror'' and ``dome'', which arise from turbulence and temperature variations that are difficult to quantify, measure directly, and ameliorate. We describe a method to determine the ``local'' seeing degradation due to wavefront perturbations within the final tens of meters of the optical path from celestial sources to a ground-based telescope, using the primary instrument and along the same path taken by light from celestial sources. The concept involves placing strobed emitters along the li…
We present an analysis of the science image quality obtained on the twin 6.5 metre Magellan telescopes over a 1.5 year period, using images of ~10^5 stars. We find that the telescopes generally obtain significantly better image quality than the DIMM-measured seeing. This is qualitatively consistent with expectations for large telescopes, where the wavefront outer scale of the turbulence spectrum plays a significant role. However, the dominant effect is found to be wind speed with Magellan outperforming the DIMMs most markedly when the wind is strongest. Excluding data taken during strong wind …
Atmospheric profiling is a requirement for controlling wide-field Adaptive Optics (AO) instruments, analyzing the AO performance with respect to the observing conditions and predicting the Point Spread Function (PSF) spatial variations. We present PEPITO, a new concept for profiling atmospheric turbulence from {\em post~facto} tip-tilt (TT) corrected short-exposure images. PEPITO utilizes the anisokinetism effect in the images between several stars separated from a reference star, and then produces the profile estimation using a model-fitting methodology, by fitting to the long exposure TT-cor…
We describe the implementation of a robotic SLODAR instrument at the Cerro Paranal observatory. The instrument measures the vertical profile of the optical atmospheric turbulence strength, in 8 resolution elements, to a maximum altitude ranging between 100 m and 500 m. We present statistical results of measurements of the turbulence profile on a total of 875 nights between 2014 and 2018. The vertical profile of the ground layer of turbulence is very varied, but in the median case most of the turbulence strength in the ground layer is concentrated within the first 50 m altitude, with relatively…
Focal-Plane Diagnostics of Atmospheric and Dome-Induced Turbulence: Exploring techniques and applications
Instituto de Astrofísica de Canarias（加那利群岛天体物理研究所）；Universidad de La Laguna（拉古纳大学）；Rhine-Waal University of Applied Sciences（莱茵-瓦尔应用科学大学）；Instituto de Radioastronomía y Astrofísica (IRyA), Universidad Nacional Autónoma de México（墨西哥国立自治大学射电天文与天体物理研究所）
Multi-conjugated adaptive optics (MCAO) yield nearly diffraction-limited images at 2$μ$m wavelengths. Currently, GeMS/GSAOI at Gemini South is the only MCAO facility instrument at an 8m telescope. Using real data and for the first time, we investigate the gain in depth and S/N when MCAO is employed for $K_{\rm s}$-band observations of distant galaxies. Our analysis is based on the Frontier Fields cluster MACS J0416.1-2403, observed with GeMS/GSAOI (near diffraction-limited) and compared against VLT/HAWK-I (natural seeing) data. Using galaxy number counts, we show that the substantially increas…
We report the atmospheric turbulence parameters namely, atmospheric seeing, the tilt-anisoplanatic angle ($θ_0$) and the coherence time ($τ_0$), measured under various sky conditions, at Vainu Bappu Observatory in Kavalur. Bursts of short exposure images of selected stars were recorded with a high-speed, frame-transfer CCD mounted on the Cassegrain focus of a newly commissioned 1.3 m telescope. The estimated median seeing is $ \approx 1.85^{\prime\prime} $ at wavelength of $\sim 600$ nm, the image motion correlation between different pairs of stars is $\sim 44\%$ for $θ_0 \approx 36^{\prime\pr…
Robo-AO is an autonomous laser guide star adaptive optics system recently commissioned at the Kitt Peak 2.1-m telescope. Now operating every clear night, Robo-AO at the 2.1-m telescope is the first dedicated adaptive optics observatory. This paper presents the imaging performance of the adaptive optics system in its first eighteen months of operations. For a median seeing value of $1.31^{\prime\prime}$, the average Strehl ratio is 4\% in the $i^\prime$ band and 29\% in the J band. After post-processing, the contrast ratio under sub-arcsecond seeing for a $2\leq i^{\prime} \leq 16$ primary star…
A defocused image of a bright single star in a small telescope contains rich information on the optical turbulence, i.e. the seeing. The concept of a novel turbulence monitor based on recording sequences of ring-like intrafocal images and their analysis is presented. It can be implemented using standard inexpensive telescopes and cameras. Statistics of intensity fluctuations in the rings and their radial motion allow measurement of the low-resolution turbulence profile, the total seeing, and the atmospheric time constant. The algorithm of processing the images and extracting the turbulence par…
The Giant Magellan Telescope (GMT) design consists of seven circular 8.4-m diameter mirror segments that are separated by large > 30 cm gaps, creating the possibility of fluctuations in optical path differences due to flexure, segment vibrations, wind buffeting, temperature effects, and atmospheric seeing. In order to utilize the full diffraction-limited aperture of the GMT for natural guide star adaptive optics (NGSAO) science, the seven mirror segments must be co-phased to well within a fraction of a wavelength. The current design of the GMT involves seven adaptive secondary mirrors, an off-…
The CHARA Array is the longest baseline optical interferometer in the world. Operated with natural seeing, it has delivered landmark sub-milliarcsecond results in the areas of stellar imaging, binaries, and stellar diameters. However, to achieve ambitious observations of faint targets such as young stellar objects and active galactic nuclei, higher sensitivity is required. For that purpose, adaptive optics are developed to correct atmospheric turbulence and non-common path aberrations between each telescope and the beam combiner lab. This paper describes the AO software and its integration int…
