Astroclimatic conditions characterize the quality of an astronomical site. The Terskol Observatory was founded over 42 years ago in 1980. The astronomical site (coordinates 43◦16′29′′ N,42◦30′03′′ E) is located about 10km from Mt. Elbrus in the northern Caucasus Mountains. The paper presents the results of an analysis astroclimatic parameters such as total cloud cover, precipitable water vapor, and wind speed at a level of 200hPa. above the Terskol Observatory using atmospheric ERA5 Reanalysis data from the European Center for Medium-Range Weather Forecast, as well as acoustic station data and optical measurements. The study of seasonal changes in the astroclimate parameters: wind speed at a level of 200mbar, as a parameter of applicability of adaptive optics (AO), altitude distribution of wind speed, which determines the requirements for AO performance, moisture content for assessing the possibility of AO operation in the IR range. The statistics of the seeing for 2023 are also provided.
The 1-meter Large Solar Vacuum Telescope (LSVT) is main instrument of the Baikal Astrophysical Observatory (BAO) of the Institute of Solar-Terrestrial Physics of Siberian Branch of Russian Academy of Sciences (ISTP SB RAS). The in-depth understanding of the Sun’s physics require optical observations of the Sun with higher and higher angular resolution. Therefore the development of adaptive optics is going for 1-meter LSVT. We present characterizations of free atmosphere from atmospheric ERA-Interim reanalysis data above BAO. The aim is estimation of the heights of turbulent layers above LSVT to select the heights of conjugation of deformable mirrors in the development of a multi-conjugated adaptive optics system. The profiles of inverse Richardson number (1/Ri), Brunt–Väisälä frequency, gradient of potential temperature and the total vertical wind shear are calculated for detection of heights in free atmosphere where most probably turbulence generation.
The cross-correlation coefficient of image jitter of a laser guide star (LGS) and a plane wave in the focal plane of the telescope is calculated. The calculation showed that such a cross-correlation function of image jitter consists of two terms. In this case, the first (main) term does not take into account the integral correlation of fluctuations in the displacement of the laser beam with the field of the dielectric permittivity of the medium, and the second one takes into account this correlation according to the Furutsu-Novikov formula. The Kolmogorov-Obukhov turbulence spectrum was used in the calculations. As a result, it turned out that the monostatic LGS has residual jitter, and this signal can be used to correct the "global" tilt of the wavefront in telescopes. Moreover, for medium-sized telescopes operating in conditions of strong turbulence, the magnitude of this random jitter of the position of the LGS will be sufficient to be used for correcting the tilt of the wave front.
The results of experiments on the phase correction of a laser beam propagating in a turbulent atmosphere are presented. A scheme was used in which the laser beam of the main radiation, formed using an adaptive optics system, propagated along a horizontal atmospheric path. To ensure the operation of the AO system, a signal was used from a reference source generated by cw-laser radiation at a wavelength of 0.532 μm, which propagated towards the main one. At the transmitter, the optical beam from the main laser is formed using the adaptive optics system and directed into the atmosphere by the Newton telescope. The main radiation laser is focused through the atmospheric layer into the receiving plane. A reflecting screen, a photodetector based on the small astronomical telescope Celestron, and a reference laser, which propagated towards the main one, were located in this plane.
The design of adaptive optics (AO) is largely determined by atmospheric conditions above the telescope site, such as optical turbulence and wind speed. Besides the requirements to laser for LGS formation are related to atmospheric parameters. In this case, the main goal is to provide a sufficient return photons flux from LGS for measurement by the wavefront sensor. The return flux from sodium laser guide star (LGS) is determined by the characteristics of the sodium layer, atmospheric transmission, geomagnetic field parameters, and the spot size of LGS in the mesosphere. The resonance fluorescence of sodium atoms in the mesosphere is affected by such atmospheric parameters, as temperature, wind, atmospheric density of molecules at height of LGS formation. The parameters listed above depend on location of telescope and have seasonal variations. The study discusses these characteristics for astronomical observatories in the Russian Federation located in middle latitudes.
The random inhomogeneities of the refractive index due to turbulent motion in the atmosphere cause a significant decrease in the theoretical resolution of an optical telescope, cause such well-known effects as scintillation, jitter, and degradation of the optical images. Adaptive optics (AO) systems with a laser guide star (LGS) are designed to eliminate the negative effects. The main limitation of LGS is the problem of measuring the global tilt. We offer the approach to using the LGS signal. The approach, where initially the LGS is considered as a point source of spherical wave with a random center is considered. The results of analytical and numerical calculations are reported. The estimation of sodium column density and height peak of sodium mesospheric layer above large Russian Observatories are presented also.
The high-altitude distributions of the Richardson number above the 6-meters Big Telescope Alt-Azimuthal of SAO RAS for astronomical site characterization are study. The 1/Ri used as parameter for ranking sites in term regime of stability and relative probability of periods and regions of turbulence. The profiles of the gradients of the potential temperature and the wind speed up to height of 25km for each month of year are calculated. The data used from the ERA-Erratum reanalysis, which is widely acknowledged as being reliable.
Laser guide stars (LGS) are becoming essential tool for adaptive optics in large ground-based telescopes. We discuss the limitations of LGS, which is the indetermination of the tilt of the incoming wavefront. Because laser guide star is usually formed with a focused laser beam directed from a telescope (from the ground), it is actually a spherical wave with a random center. Taking this into account, the residual distortions of phase fluctuations are calculated. The analytical calculation carried out in the approximation of the Huygens-Fresnel method.
The quality of astronomical observations is strongly related to the quality properties of the atmosphere. The studies of the atmosphere above observing sites are important for observation planning, instrument optimization, adaptive optics development. The high-altitude distributions of wind speed over the 6-meters Big Telescope Alt-Azimuthal of Special Astrophysical Observatory of Russian Academy Science for astronomical site characterization and the development of adaptive optics techniques are study. The data used from the NCEP/NCAR and ERA-Interium reanalysis, which is widely acknowledged as being reliable. Seasonal behaviors (mean, median, quantiles) of vertical distributions of wind speed are presented. Statistical analyses of the 200-mbar wind speed used as useful parameter for ranking astronomical sites in term of their suitability for adaptive optics is performed. The long-time trend of V200 is presented.
The temporal error is the main problem for adaptive optical systems operating in the atmosphere. One way to solve this problem is to optimize the adaptive optics system by predictive control algorithms. In study the adaptive optical system installed on the small-aperture telescope with the predictive algorithm are developed. The predictive algorithm uses measurement of center gravity of light intensity at subapertures of the Shack-Hartmann wavefront sensor has been developed. In results it not depends on the type and design of the adaptive mirror. For implementation the Shack- Hartmann wavefront sensor measuring phase distortion, atmospheric turbulence, and transverse wind velocity are created. The design of the wavefront sensor allows replacement of the microlens array with different sizes, focal lengths and operated in wide range of phase aberrations. As a result, the adaptive optics system measure the level of optical atmospheric turbulence for replace the microlens array and it to operated in different turbulent atmospheric conditions.
The temporal error of the adaptive optical system leads to a significant degradations in the characteristics of the system operating in the atmosphere. One of the methods for solving this problem is the use of prediction algorithms based on the analysis of the evolution of phase fluctuations. In the paper the wavefront sensor as the key element of atmospheric adaptive optical system with predictions algorithms is considered. The results of the development and testing of the Shack-Hartmann wavefront sensor providing measurements of phase fluctuations, determination of the Fried parameter and wind speed using original design solutions and software are presented. The practical and theoretical aspects of using the Shack-Harmann wavefront sensor are discussed. For it dynamic range, sensitivity and accuracy of the sensor are estimated. The influences of parameters of microlens array on range of measurements of the Shack-Harmann wavefront sensor are studied. The tests of the S-H WFS were carry out with acoustic measurements of wind speed and the structural constant of the refractive index of the atmosphere, as well as in adaptive optics system in laboratory test bench.
We describes the status of AO test bench, which is developing at the Adaptive optics Lab, V.E. Zuev Institute of Atmospheric Optics of the Siberian Branch of the Russian Academy of Sciences (IAO SB RAS), Tomsk, Russia to simulate predictive algorithms of wavefront adaptive correction. The description of the optical and mechanical design, components AO bench, and the working principle and first experimental results are presented. The current AO test bench consists of laser source, two deformable mirrors with 59 actuators and 56 mm diameter (Visionica Ltd., Russia), two tip/tilt mirrors (IAO SB RAS, Russia), Shack-Hartmann Wavefront Sensor (WFS), which we specially designed, and a science camera for the evaluation of the performance. The user derived aberrations are introduced using a one deformable mirror and corrected by another deformable mirror. The tip/tilt mirrors are used for predictive control of the low-order wavefront aberrations related such as vibrations.
The Baikal Astrophysical Observatory of Institute Solar- Terrestrial Physics of Siberian Branch of Russian Academy Sciences is located at an altitude of about 700 meter above sea level on the shore of Lake Baikal, Russian Federation. Large Solar Vacuum Telescope (LSVT) is the main telescope of the Baikal Astrophysical Observatory. We develop models of vertical profile of atmospheric turbulence (the refractive-index structure constant) and wind speed at the BAO for adaptive optical system design of LSVT. We also presented vertical profile wind speed and the refractive-index structure constant is obtained from NCEP/NCAR Reanalysis base.
We study seasonal variations of the vertical distribution of wind speed at the Baikal Astrophysical Observatory (BAO) using NCEP/NCAR Reanalysis data base for development of adaptive optical system of Large Solar Vacuum Telescope (LSVT). The statistics of wind speed including mean and median profile, the first and third quartiles are calculated. Also we analyzed seasonal variations of wind speed on the pressure level 200-mbar, as parameter for estimation of suitable of the site for adaptive optics and level of atmospheric optical turbulence.
The optical turbulence characteristics statistics including "seeing", Fried radius, wind speed height profiles are discussed. Distribution of the mean Fried radius obtained from the data of image motion measurements by the Brandt sensor is given. Also, the Fried radius values calculated from the Shack-Hartmann data are given. Using the height profile of the structure characteristic of air refractive index fluctuations obtained from spectral multiscale turbulence model the results of the Fried radius simulations from micrometeorological mast measurement data given.
The features of air index refraction vertical variations up to 20 km at the Large solar vacuum telescope site are discussed. The possible local model of air index refraction fluctuations are supposed at the Large solar vacuum telescope site.
In this article, we describe the development of the newest adaptive optics system for the Big Solar Vacuum Telescope of the Baikal Astrophysical Observatory. This system is a result of collaboration between VE Zuev Institute of Atmospheric Optics SB RAS, Tomsk, and Institute of Solar-Terrestrial Physics SB RAS, Irkutsk. The system includes two active mirrors for the correction: domestic tip-tilt and bimorph deformable (Active Optics NightN Ltd.), and separate wavefront sensors (WFS). A correlation S-H wave-front sensor is based on a Allies Prosilica GX-1050 GigE camera with speed of 309 Hz and frame size of 1248x1248 pixels. A personal computer is used for bimorph deformable mirror image processing. The mirror was successfully used during the 2010–2014 observing seasons. The system developed is capable of correcting up to 35 modes, thus providing diffraction limited images at visible wavelengths.
The criteria image qualities based on wave front aberration caused by atmospheric turbulence using in adaptive optics are summarized. Atmospheric turbulence profile for Big Solar Vacuum Telescope (BSVT) observatory is obtained based on satellite date. On this based the development of adaptive optics systems of BSVT are discussed.
The passive differential method of measuring of maintenance in the atmosphere of atoms of sodium is offered in a mesosphere with the use of solar radiation. With sufficient good exactness relation of irradiances of the Sun on two near, such that aerosol dispersion and weakening practically identically, wavelengths equal as (λ1/λ2 ))5 . On the basis of analysis of relation of irradiances of a Sun on two wavelengths it is possible to determine the relative changes of maintenance of atoms of sodium in the whole atmospheric colomn.
Experimental data of our turbulence measurements (by ultrasonic digital sensors) in the various areas and meteosituations show that large areas are often observed in open atmosphere, in which one large coherent structure has the main influence. Turbulence in such areas is called as coherent. Incoherent Kolmogorov turbulence is detecting, as a rule, on sites with a flat surface. Coherent turbulence differs from Kolmogorov turbulence by the faster decrease of a time spectrum in an inertial interval (f – 8/ 3 instead of f – 5/ 3) and the smaller contribution of the high-frequency components.
During a period of more than 30 years we have performed successively investigations of the effect of low-frequency spectral range of atmospheric turbulence on the optical characteristics. The influence of the turbulence models as well as a outer scale of turbulence on the characteristics of telescopes and systems of laser beam formations has been determined too. This question is important in, for example, problems of ground-based astronomy.
There is analyzed the possibility the general tilt correction of the wave front on base of the laser guide star
(LGS) signal. The calculation of the image motion of the spherical wave (that position the source of radiation
also fluctuated) with random center is conducted. The exact formula for random vector defining the position of
the image of the spherical wave in focal plane of the telescope is offered.
The variance of residual fluctuations has been calculated. The variance behavior of this residual motion from
optical experiment parameters are analyses. The similar problem under solution of the some practical tasks,
including the possibility of the wave front "global" tilt correction with using single LGS, can be appeared.
In report we review aspects related to the implementation of laser guide star (LGS) in an adaptive optics (AO)
system. As soon as lasers were proposed to create guide star for adaptive optics, it was realized that the LGS could
not be used to measure tilt. In report the analysis of the possibility of tilt-measurement in the framework of using a
LGS are discussed. Results of analytical calculations where assumptions made earlier remove are presented. We
suggested the use the algorithm of 'optimal' correction for determination correction the wavefront aberration of the
science object by means of the measured wavefront LGS. The analytical and numerical calculations are presented.
For numerical calculation we used set the various model of turbulence profile. The significant increases in efficiency
of phase correction based on this algorithm are achieved.
There is analyzed the possibility the general tilt correction of the wave front on base of the laser guide star (LGS) signal.
The calculation of the image motion of the spherical wave (that position the source of radiation also fluctuated) with
random center is conducted. The exact formula for random vector defining the position of the image of the spherical
wave in focal plane of the telescope is offered.
The variance of residual fluctuations has been calculated. The variance behavior of this residual motion from optical
experiment parameters are analyses. The similar problem under solution of the some practical tasks, including the
possibility of the wave front "global" tilt correction with using single LGS, can be appeared.
Simple analytical expressions for parameter Strehl of ground-based astronomical telescope: (i) without adaptive
correction, (ii) phase correction with use single laser guide star, (iii) phase correction with use multi-guide stars (square matrix
system of guide stars with variable number of elements) are obtained. Models of the vertical dependence of the structure
parameter of refractive index of the turbulent atmosphere for various sites are used in the calculations. Modal phase correction is
considered to large aperture ground-based telescope with multi-guide stars. Wave aberrations presented in the in terms of Zernike
polynomials are used to calculate the angular correlation of modal components of phase fluctuations of optical radiation
propagating in the turbulent atmosphere. The size of the isoplanatic area in an adaptive optical system is studied. The influence of
the model of vertical profile of the structure parameter of atmospheric refractive index fluctuations, the outer scale of atmospheric
turbulence, and the size of receiving aperture of a telescopic system are analyzed. Requirements on bandwidth of adaptive optical
system for effective correction are formulated.
The image quality is analyzed of an extraterrestrial object formed by astronomical optical system through the turbulent
atmosphere. Relative increase the Strehl parameter is calculated under adaptive correction based on the laser guide star
technique. The efficiency of adaptive correction of distortions for different type of the guide sources is compared. The
calculations are performed for different models of the vertical variations of the structural parameter of the refractive
index of the turbulent atmosphere. For a set of guide stars application the higher correction and big increase of the Strehl
parameter are obtained, that is indirect evidence of the good correction of the higher mode components, which are badly
corrected using the traditional techniques. As comparative calculations for different models of vertical variations of the
structural parameter of the refractive index have shown, there are serious differences in the behaviors of the correlation
radii for the plane and spherical waves.
We analyze the image quality of an extraterrestrial object imaged by astronomical optical systems through the turbulent atmosphere. The relative increase of the Strehl parameter is calculated under adaptive corrections with laser guide star. We compare the efficiency of adaptive correction for different types of the guide sources. The calculations are performed for different models of the vertical distribution of the structural parameter of the refractive index of the turbulent atmosphere. A special wavefront sensor is applied, which operates with a full-aperture collimated laser beam as a reference wave. This layer-oriented wavefront sensor is used to reconstruct the continuous phase of the reference wave. Our results show that the parameters of the reconstructed field are quite close to that of a plane wave. A significant increase of the Strehl parameter indicates excellent correction of higher order modes, which are usually difficult to sense and correct with traditional LGS techniques using a focused laser beam. A comparative analysis of various atmospheric models revealed some noticeable differences in correlation radii for the plane and spherical waves.
We propose a modified approach to form a laser guide star (LGS) with a wide, collimated laser beam launched
through the full aperture of a telescope. Using a special form of field stop (diaphragm) uniquely positioned for each
subapertures, the wavefront sensor "sees" only a small part of the source corresponding to the area on the sky, which is
cut out by the field stop. Each of these spherical waves subtends the area of a separate subaperture at the telescope pupil.
Thus, the LGS is formed of a set of spherical waves. Since the linear size of the subaperture is approximately equal to the
coherence radius, the measured wavefront can be restored as a smooth phase function. In the paper use of this scheme is
investigated.
It is well know that adaptive optical system (AOS) operating on astronomical telescopes with a LGS has limitations due
to the effect of the focal anisoplanatism, since the spherical wavefront that comes from the LGS does not pass trough the
same portion of turbulence atmosphere as plane wavefront of natural guide stars (NGS) located at an infinite distance
from ground. There have been proposed several different approaches to overcome the focal anisoplanatism. In the
method proposed by Buscher et al, sensing of the turbulence-induced wavefront distortions is performed on the
outgoing path of a collimated laser beam by forming an extended intensity pattern in the atmosphere and analyzing its
distortion from the ground. In a recent work, the prospect of using a collimated laser beam launched through the main
telescope has been revisited and a special wavefront sensing scheme has been proposed. In the present paper we show
possible implementation for this scheme and give analytical analysis of AOS performance.
The image quality is analyzed of an extraterrestrial object formed by astronomical optical system through the turbulent
atmosphere. Relative increase the Strehl parameter is calculated under adaptive correction based on the laser guide star
technique. The efficiency of adaptive correction of distortions for different type of the guide sources is compared. A
special wave front sensor is applied, which operates using the broad laser beam as a reference wave. The calculations are
performed for different models of the vertical variations of the structural parameter of the refractive index of the
turbulent atmosphere. The wave front sensor was used, which enables to reconstruct the continuous phase of the
reference wave. As the estimates show, the parameters of the formed field are quite close to that plane wave. So the
higher correction and big increase of the Strehl parameter are obtained, that is indirect evidence of the good correction of
the higher mode components, which are badly corrected using the traditional techniques for formation of LGS by means
of a focused laser beam. As comparative calculations for different models of vertical variations of the structural
parameter of the refractive index have shown, there are serious differences in the behaviors of the correlation radii for the
plane and spherical waves.
As a result of the accomplish experiments determine, that by a method of a laser-induced fluorescence of chlorophyll it is possible to spot for cedar an early stage of the stressful factor, bound with presence in ground ≪petroleum dirt≫. In our case the laboratory researches provided learning a quantitative contents chlorophyll for plants found in normal and stressful conditions on a basis spectrophotometrical of a method. Natural measurement the observations behind dynamics of a photosynthetic state means of wood plants in vivo enable. For an estimation of this state the fluorescence of chlorophyll on wavelength 685 and 740 nm was used. The optical model of a green leaf was developed for methods of a laser-induced fluorescence of chlorophyll. A experiments series on remote research of processes violation of mineral power supply and exchange in plants is carried spent. Was considered the change of the ratios of intensity of a fluorescence of chlorophyll and carotenoids at deficiency. Was designed technique for detection infringement processes of mineral nutrition and change surveyed acidity grounds on laser-induce fluorescent responses of deciduous plants.
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