Recalibrated turbulence profiles at San Pedro M��rtir (original) (raw)
Related papers
Turbulence Profiles with Generalized Scidar at San Pedro Mártir Observatory and Isoplanatism Studies
Publications of the Astronomical Society of the Pacific, 1998
The results obtained from 3398 vertical pro les of atmospheric turbulence measured during 11 nights at the Observatorio Astron omico Nacional in San Pedro M artir (Baja California, M exico) are presented. The observations were carried out with the generalized scidar (GS) installed at the 1.5 m and the 2.1 m telescopes of that site, in March and April 1997. The open air seeing was measured with a di erential image motion monitor (DIMM). The GS can detect turbulence pro les along the whole optical path, unlike the classical scidar which is insensitive to low altitude turbulence. For the rst time, to our knowledge, pro les including turbulence near the ground are monitored and statistically analyzed. Isoplanatic angles for speckle interferometry and adaptive optics (AO) in either full or partial compensation are deduced, as well as the focus anisoplanatism parameter for sodium laser guide stars. The advantage of minimizing the distance between the turbulent layers and the conjugated plane of the deformable mirror of an AO system is studied. The comparison of GS pro les obtained at both telescopes, together with DIMM measurements, show that the turbulence near the ground is more strongly dominant at the 1.5 m telescope than at the 2.1 m telescope, where the median values of the seeing near the ground, in the free atmosphere and in the whole optical path are 0.56, 0.44 and 0.77 arcsec, respectively. These values are comparable to or better than those of the major astronomical observatories, although a larger data sample is needed for a de nitive comparison.
Whole atmospheric-turbulence profiling with generalized scidar
Applied Optics, 1997
Statistical analysis of stellar scintillation on the pupil of a telescope, known as the scidar ͑scintillation, detection, and ranging͒ technique, is sensitive only to atmospheric turbulence at altitudes higher than a few kilometers. With the generalized scidar technique, recently proposed and tested under laboratory conditions, one can overcome this limitation by analyzing the scintillation on a plane away from the pupil. We report the first experimental implementation of this technique, to our knowledge, under real atmospheric conditions as a vertical profiler of the refractive-index structure constant C N 2 ͑h͒. The instrument was adapted to the Nordic Optical Telescope and the William Hershel Telescope at La Palma, Canary Islands. We measure the spatial autocorrelation function of double-star scintillation for different positions of the analysis plane, finding good agreement with theoretical expectations.
Ground-based and Airborne Telescopes II, 2008
Since November 2004 we measured the optical turbulence (C 2 N profiles) with a Generalized Scidar (GS) placed at the focus of the Vatican Advanced Technology Telescope at Mt.Graham, Arizona. The present statistic consists in measurements related to 43 nights covering different periods of the solar year. In this paper we calculate the statistics of the astroclimatic parameters (C 2 N , seeing ε , isoplanatic angle θ 0 , wavefront coherence time τ 0 ) and we compare these values with those measured above other top level astronomic sites. All profiles are reduced into a form suitable to be used as inputs for adaptive optics point spread function simulations for the conceptual design of the Laser Guide Star Facility supported by a GLAO system of the Large Binocular Telescope. With GS measurements done observing wide binaries (30-35 arcsec), the turbulence in the first kilometer above the ground is characterized with the vertical resolution (200-250 m) required for the optimization of a 4 arcmin field of view AO system. It is the first time that are published measurements of the optical turbulence vertical distribution above a mid-latitude site with such a high vertical resolution and such a high statistical reliability. On 8 of those nights, employing cross-correlation scintillation maps of wide binaries and the method described in Ref.
Turbulence and wind profiling with generalized scidar at Cerro Pachon
SPIE Proceedings, 2000
We present the rst simultaneous monitoring of the vertical distributions of the optical turbulence strenght C 2 N (h) and the wind velocity V(h), along the whole optical path. For that purpose, a new algorithm has been developed for the analysis of the spatio-temporal correlation of scintillation images, obtained with the Generalized Scidar (GS). The algorithm allows for dome seeing identi cation. The new method has being applied to the GS data collected during four one-week runs uniformely distributed during 1998, for the characterization of Cerro Pach on, the Gemini South Telescope site. Comparison of V(h) obtained with the GS and instrumented balloons, respectively, gives a great deal of con dence in the new method. The analysis of the 6900 C 2 N (h) and V(h) pro les obtained, leads to a statistical study of the most important parameters relevant for the development of adaptive optical systems.
Two campaigns to compare three turbulence profiling techniques at Las Campanas Observatory
2008
In preparation to characterize the Giant Magellan Telescope site and guide the development of its adaptive optics system, two campaigns to systematically compare the turbulence profiles obtained independently with three different instruments were conducted at Las Campanas Observatory in September, 2007 and January 2008. Slope detection and ranging (SLODAR) was used on the 2.5-m duPont telescope. SLODAR measures the C2n profile as a function of altitude through observations of double stars. The separation of the observed double star sets the maximum altitude and height resolution. Ground layer (altitudes < 1 km) and free atmosphere turbulence profiles are compared with those obtained with a lunar scintillometer (LuSci) and a multi-aperture scintillation sensor (MASS), respectively. In addition, the total atmospheric seeing was measured by both SLODAR and a differential image motion monitor (DIMM).
Recalibrated generalized SCIDAR measurements at Cerro Paranal (the site of the Very Large Telescope)
Monthly Notices of the Royal Astronomical Society, 2012
Generalized SCIDAR (GS) measurements, which were taken at the Paranal Observatory in 2007 November/December in the context of a site qualification for the future European Extremely Large Telescope, are recalibrated to overcome the bias induced on the C 2 N profiles by an incorrect normalization of the autocorrelation of the scintillation maps, which has recently been identified in the GS technique. A complete analysis of the GS-corrected measurements and the corrected errors is performed statistically as well as on individual nights, and for each time period during the nights. The relative errors of the C 2 N profiles can reach up to 60 per cent in some narrow temporal windows and some vertical slabs, with the total seeing up to 12 per cent and the total integrated turbulence J up to 21 per cent. However, the statistical analysis shows that the absolute error of the median values of the total seeing is 0.06 arcsec (relative error 5.6 per cent); for the boundary seeing it is 0.05 arcsec (relative error 5.6 per cent) and for the seeing in the free atmosphere it is 0.04 arcsec (relative error 9 per cent). We find that, in spite of the fact that the relative error increases with the height, the boundary and the free atmosphere seeing contribute in an equivalent way to the error on the total seeing in absolute terms. Moreover, we find that there are no correlations between the relative errors and the value of the corresponding seeing. The absolute error of the median value of the isoplanatic angle is 0.13 arcsec (relative error 6.9 per cent).
Optical turbulence profiling with Stereo-SCIDAR for VLT and ELT
Monthly Notices of the Royal Astronomical Society, 2018
Knowledge of the Earth's atmospheric optical turbulence is critical for astronomical instrumentation. Not only does it enable performance verification and optimization of the existing systems, but it is required for the design of future instruments. As a minimum this includes integrated astro-atmospheric parameters such as seeing, coherence time, and isoplanatic angle, but for more sophisticated systems such as wide-field adaptive optics enabled instrumentation the vertical structure of the turbulence is also required. Stereo-SCIDAR (Scintillation Detection and Ranging) is a technique specifically designed to characterize the Earth's atmospheric turbulence with high-altitude resolution and high sensitivity. Together with ESO (European Southern Observatory), Durham University has commissioned a Stereo-SCIDAR instrument at Cerro Paranal, Chile, the site of the Very Large Telescope (VLT), and only 20 km from the site of the future Extremely Large Telescope (ELT). Here we provide results from the first 18 months of operation at ESO Paranal including instrument comparisons and atmospheric statistics. Based on a sample of 83 nights spread over 22 months covering all seasons, we find the median seeing to be 0.64 with 50 per cent of the turbulence confined to an altitude below 2 km and 40 per cent below 600 m. The median coherence time and isoplanatic angle are found as 4.18 ms and 1.75 , respectively. A substantial campaign of inter-instrument comparison was also undertaken to assure the validity of the data. The Stereo-SCIDAR profiles (optical turbulence strength and velocity as a function of altitude) have been compared with the Surface-Layer Slope Detection And Ranging, Multi-Aperture Scintillation Sensor-Differential Image Motion Monitor, and the European Centre for Medium Range Weather Forecasts model. The correlation coefficients are between 0.61 (isoplanatic angle) and 0.84 (seeing).
LOLAS-2: Redesign of an Optical Turbulence Profiler with High Altitude-resolution
Publications of the Astronomical Society of the Pacific, 2016
We present the development, tests and first results of the second generation Low Layer Scidar (LOLAS-2). This instrument constitutes a strongly improved version of the prototype Low Layer Scidar, which is aimed at the measurement of optical turbulence profiles close to the ground, with high altitude-resolution. The method is based on the Generalised Scidar principle which consists in taking double-star scintillation images on a defocused pupil plane and calculating in real time the autocovariance of the scintillation. The main components are an open-truss 40-cm Ritchey-Chrétien telescope, a german-type equatorial mount, an Electron Multiplying CCD camera and a dedicated acquisition and real-time data processing software. The new optical design
Optical turbulence vertical distribution with standard and high resolution at Mt Graham
Monthly Notices of the Royal Astronomical Society, 2010
A characterization of the optical turbulence vertical distribution (C 2 N profiles) and all the main integrated astroclimatic parameters derived from the C 2 N and the wind speed profiles above the site of the Large Binocular Telescope (LBT) (Mt Graham, Arizona, USA) is presented. The statistics include measurements related to 43 nights done with a Generalized SCIDAR (GS) used in standard configuration with a vertical resolution H ∼ 1 km on the whole 20 km and with the new technique (High Vertical Resolution GS) in the first kilometre. The latter achieves a resolution H ∼ 20-30 m in this region of the atmosphere. Measurements done in different periods of the year permit us to provide a seasonal variation analysis of the C 2 N . A discretized distribution of C 2 N , useful for the Ground Layer Adaptive Optics (GLAO) simulations, is provided and a specific analysis for the LBT Laser Guide Star system ARGOS (running in GLAO configuration) case is done including the calculation of the 'grey zones' for J, H and K bands. Mt Graham is confirmed to be an excellent site with median values of the seeing without dome contribution ε = 0.72 arcsec, the isoplanatic angle θ 0 = 2.5 arcsec and the wavefront coherence time τ 0 = 4.8 ms. We find that the OT vertical distribution decreases in a much sharper way than what has been believed so far in the proximity of the ground above astronomical sites. We find that 50 per cent of the whole turbulence develops in the first 80 ± 15 m from the ground. We finally prove that the error in the normalization of the scintillation that has been recently demonstrated in the principle of the GS technique affects these measurements by an absolutely negligible quantity (0.04 arcsec).