Results of 2005-2007 campaign of measurement of the optical turbulence vertical distribution above Mt. Maidanak are presented. Measurements are performed with the MASS (Multi-Aperture Scintillation Sensor) device which is widely used in similar studies during last years at several observatories across the world. The data analysis shows that median seeing in free atmosphere (at altitudes above 0.5km) is 0.46 arcsec and median isoplanatic angle is 2.47 arcsec. Given a rather long atmospheric coherence time (about 7 ms when the seeing is good) such conditions are favorable for adaptive optics and interferometry in the visible and near-IR.
The Profiler of Moon Limb is a recent instrument dedicated to the monitoring of optical turbulence profile of the atmosphere. Fluctuations of the Moon or the Sun limb allow to evaluate the index refraction structure constant C_n^2(h) and the wavefront coherence outer scale L_0(h) as a function of the altitude $h$. The atmosphere is split into 33 layers with an altitude resolution varying from 100m (at the ground) to 2km (in the upper atmosphere). Profiles are obtained every 3mn during daytime and nighttime. We report last advances on the instrument and present some results obtained at the Plat…
The strength and vertical distribution of atmospheric turbulence is a key factor determining the performance of optical and infrared telescopes, with and without adaptive optics. Yet, this remains challenging to measure. We describe a new technique using a sequence of short-exposure images of a star field, obtained with a small telescope. Differential motion between all pairs of star images is used to compute the structure functions of longitudinal and transverse wavefront tilt for a range of angular separations. These are compared with theoretical predictions of simple turbulence models by me…
We present a simple method of extracting a small number of reference optical turbulence and wind profiles from a large dataset for single conjugate and extreme adaptive optics simulations. These reference profiles can be used in slow end-to-end adaptive optics simulations to represent the variability of the atmosphere. The method is based on the assumption that performance for these systems is correlated with integrated atmospheric parameters $r_0$, $θ_0$ and $τ_0$. Profiles are selected from a large dataset that conform concurrently to the distributions of these parameters, and hence represen…
We present very encouraging preliminary results obtained in the context of the MOSE project, an on-going study aiming at investigating the feasibility of the forecast of the optical turbulence and meteorological parameters (in the free atmosphere as well as in the boundary and surface layer) at Cerro Paranal (site of the Very Large Telescope - VLT) and Cerro Armazones (site of the European Extremely Large Telescope - E-ELT), both in Chile. The study employs the Meso-Nh atmospheric mesoscale model and aims at supplying a tool for optical turbulence forecasts to support the scheduling of the sci…
In two recent papers the mesoscale model Meso-NH, joint with the Astro-Meso-NH package, has been validated at Dome C, Antarctica, for the characterization of the optical turbulence. It has been shown that the meteorological parameters (temperature and wind speed, from which the optical turbulence depends on) as well as the Cn2 profiles above Dome C were correctly statistically reproduced. The three most important derived parameters that characterize the optical turbulence above the internal antarctic plateau: the surface layer thickness, the seeing in the free-atmosphere and in the total atmos…
This paper analyses 3.5 years of site testing data obtained at Dome C, Antarctica, based on measurements obtained with three DIMMs located at three different elevations. Basic statistics of the seeing and the isoplanatic angle are given, as well as the characteristic time of temporal fluctuations of these two parameters, which we found to around 30 minutes at 8 m. The 3 DIMMs are exploited as a profiler of the surface layer, and provide a robust estimation of its statistical properties. It appears to have a very sharp upper limit (less than 1 m). The fraction of time spent by each telescope ab…
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…
Atmospheric scintillation caused by optical turbulence in the Earth's atmosphere can be the dominant source of noise in ground-based photometric observations of bright targets, which is a particular concern for ground-based exoplanet transit photometry. We demonstrate the implications of atmospheric scintillation for exoplanet transit photometry through contemporaneous turbulence profiling and transit observations. We find a strong correlation between measured intensity variations and scintillation determined through optical turbulence profiling. This correlation indicates that turbulence prof…
The results on the vertical distribution of optical turbulence above the five mountains which were investigated by the site testing for the Thirty Meter Telescope (TMT) are reported. On San Pedro Martir in Mexico, the 13 North site on Mauna Kea and three mountains in northern Chile Cerro Tolar, Cerro Armazones and Cerro Tolonchar, MASS-DIMM turbulence profilers have been operated over at least two years. Acoustic turbulence profilers - SODARs - were also operated at these sites. The obtained turbulence profiles indicate that at all sites the lowest 200m are the main source of the total seeing …
Measurements of the optical turbulence profile above Siding Spring Observatory were conducted during 2005 and 2006. This effort was largely motivated by the need to predict the statistical performance of adaptive optics at Siding Spring. The data were collected using a purpose-built instrument based on the slope-detection and ranging method (SLODAR) where observations of a bright double star are imaged by Shack-Hartmann taken with the Australian National University 24 inch and 40 inch telescopes. The analysis of the data yielded a model consisting of a handful of statistically prominent thin l…
We describe the realization of a 5 km free space coherent optical link through the turbulent atmosphere between a telescope and a ground target. We present the phase noise of the link, limited mainly by atmospheric turbulence and mechanical vibrations of the telescope and the target. We discuss the implications of our results for applications, with particular emphasis on optical Doppler ranging to satellites and long distance frequency transfer.
Optical turbulence affects significantly the quality of ground-based astronomical observations. An accurate and reliable forecast of optical turbulence can help to optimise the scheduling of the science observations and to improve both the quality of the data and the scientific productivity of the observatory. However, forecasts of the turbulence to a level of accuracy that is useful in the operations of large observatories are notoriously difficult to obtain. Several routes have been investigated, from detailed physical modelling of the atmosphere to empirical data-driven approaches. Here, we…
The mesoscale model Meso-NH is used to simulate the optical turbulence at Mt Graham (Arizona, USA), site of the Large Binocular Telescope. Measurements of the CN2-profiles obtained with a generalized scidar from 41 nights are used to calibrate and quantify the model's ability to reconstruct the optical turbulence. The measurements are distributed over different periods of the year, permitting us to study the model's performance in different seasons. A statistical analysis of the simulations is performed for all the most important astroclimatic parameters: the CN2-profiles, the seeing ε, the is…
Laser communication has advances in compared with radio frequency communication as result of much high carrier frequency from ultraviolet to near infrared. Very narrow laser beam is possible to form with very high power density. But laser beam has high destruction and attenuation on clouds, turbulence, scattering on aerosols and molecules of the atmosphere. Low Earth orbits (LEO), Middling Earth orbits (MEO) and partly Geosynchronous Earth orbit (GSO) satellites moving on the sky and laser light from satellites moves across different turbulence conditions of the atmosphere, clouds, molecules o…
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…
The internal antarctic plateau revealed in the last years to be a site with interesting potentialities for the astronomical applications due to the extreme dryness and low temperatures, the typical high altitude of the plateau, the weak level of turbulence in the free atmosphere down to a just few tens of meters from the ground and the thin optical turbulence layer developed at the ground. The main goal of a site testing assessment above the internal antarctic plateau is to characterize the site (optical turbulence and classical meteorological parameters) and to quantify which is the gain we m…
For extremely large telescopes, adaptive optics will be required to correct the Earth's turbulent atmosphere. The performance of tomographic adaptive optics is strongly dependent on the vertical distribution (profile) of this turbulence. An important way in which this manifests is the tomographic error, arising from imperfect measurement and reconstruction of the turbulent phase at altitude. Conventionally, a small number of reference profiles are used to obtain this error in simulation however these profiles are not constructed to be representative in terms of tomographic error. It is therefo…
Advanced adaptive optics (AO) instruments on ground-based telescopes require accurate knowledge of the atmospheric turbulence strength as a function of altitude. This information assists point spread function reconstruction, AO temporal control techniques and is required by wide-field AO systems to optimize the reconstruction of an observed wavefront. The variability of the atmosphere makes it important to have a measure of the optical turbulence profile in real time. This measurement can be performed by fitting an analytically generated covariance matrix to the cross-covariance of Shack-Hartm…
Instabilities and turbulence extending to the smallest dynamical scales play important roles in the deposition of energy and momentum by gravity waves throughout the atmosphere. However, these dynamics and their effects have been impossible to quantify to date due to lack of observational guidance. Serendipitous optical images of polar mesospheric clouds at ~82 km obtained by star cameras aboard a cosmology experiment deployed on a stratospheric balloon provide a new observational tool, revealing instability and turbulence structures extending to spatial scales < 20 m. At 82 km, this resolutio…
In a recent paper the authors presented an extended study aiming at simulating the classical meteorological parameters and the optical turbulence at Dome C during the winter with the atmospherical mesoscale model Meso-NH. A statistical analysis has been presented and the conclusions of that paper have been very promising. Wind speed and temperature fields revealed to be very well reconstructed by the Meso-NH model with better performances than what has been achieved with the European Centre for Medium-Range Weather Forecast (ECMWF) global model, especially near the surface. All results reveale…
Conventional ground-based astronomical observations suffer from image distortion due to atmospheric turbulence. This can be minimized by choosing suitable geographic locations or adaptive optical techniques, and avoided altogether by using orbital platforms outside the atmosphere. One of the promises of optical intensity interferometry is its independence from atmospherically induced phase fluctuations. By performing narrowband spectral filtering on sunlight and conducting temporal intensity interferometry using actively quenched avalanche photon detectors (APDs), the Solar $g^{(2)}(τ)$ signat…
