P. G. Kovadlo

Features of optical image jitter in a random medium with a finite outer scale

Features of optical wave fluctuations while propagating through a randomly inhomogeneous turbulent medium with a finite outer scale are considered, including conditions when areas with dominating influence of one large-scale coherent structure are observed in the atmosphere, for which the spectrum of atmospheric turbulence can differ significantly from the Kolmogorov-model spectrum. Using an approximate model of the spectrum for coherent turbulence, described earlier in our works, the variance of jitter of an optical image is calculated (under the applicability condition for the smooth perturbation method). The comparison of these equations with known similar equations for Kolmogorov turbulence has shown that the variance of fluctuations are significantly weaker in coherent turbulence than in the Kolmogorov theory under similar conditions. This means that phase fluctuations of optical radiation decrease significantly in coherent turbulence. The importance of this conclusion is noted for interpretation of the results of optical sounding of atmospheric turbulence.

Estimation of the astronomical seeing at the large solar vacuum telescope site from optical and meteorological measurements

Results of synchronous optical and meteorological measurements of Fried’s coherence length at the Large Solar Vacuum Telescope are presented. A decrease in this parameter in winter time is revealed. Spectra of wind speed and temperature inhomogeneities are studied during measurements of the Fried’s length.

Modified correlation tracker algorithm for tip-tilt correction system and project ANGARA on the Big Solar Vacuum Telescope

The possibility of applying adaptive correction to ground-based solar astronomy is considered. Several experimental systems for image stabilization are described along with the results of their tests. As a result of the installation of the first order adaptive-optics system, the Big Solar Vacuum Telescope (BSVT) acquired the new quality. Different ways of development of an adaptive correction to be used in the BSVT of the Baikal Astrophysical Observatory are discussed.

Adaptive optics system for solar telescope operating under strong atmospheric turbulence

New results obtained within Russian Science Foundation Project no. 15-19-20013 are presented. The project was started in the middle of 2015 and is aimed at the solution of actual problems of the development of the optoelectronic industry using adaptive optics for astronomy, laser, and other applications. The progress in the development of the up-to-date adaptive optics system for the largest Russian solar telescope, i.e., the 1-m Big Solar Vacuum Telescope of the Baikal Astrophysical Observatory, is described.

Dynamics of the refractive properties of the atmosphere at the Big solar vacuum telescope site: new calculating method

The dynamics of turbulent characteristics including air index refraction vertical variations as well as effective turbulent velocity important for the functioning of the Large solar vacuum telescope (LSVT) adaptive optics system is considered. Long-term changes of the effective turbulent velocity and Fried radius in the atmospheric layer from 0 to 20 km are estimated using model of turbulence taking into account the shape of the energy spectrum over a wide range of spatial and temporal scales. The possible experimental local model of Fried radius changes is discussed for the Large solar vacuum telescope site.

The study of variability of the atmospheric turbulence in the region Lake Baykal

The estimations of the Fried parameter according to micrometeorological and optical measurements in the atmospheric surface layer in the area of l. Baikal, Baikal astrophysical Observatory (BAO). According to the archive of NCEP/NCAR Reanalysis data obtained vertical distribution of temperature pulsations, and revealed the most pronounced atmospheric layers with high turbulence. It is established that the values of the fried parameter at the location of the BAO are in the range from 1.5 to 5.5 cm in inter, the atmospheric coherence radius is characterized by low values of the Fried parameter. Turbulyzed atmospheric layers of the atmosphere located at an altitude of about 2.5 km and 11.5 km above the observatory, respectively. The average values of the fried radius is 4.6 cm.

Adaptive system for solar telescopes operating in the strongly turbulent atmosphere

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.

Automation system for the large solar vacuum telescope

The architecture, composition, specific features of operation, and technical characteristics of an automated control system of the Large Solar Vacuum Telescope of the Baikal astrophysical observatory are considered. The system is used for automation of both the observation process (automatic telescope guiding to the Sun, selection of a needed region in the solar disk image, guiding based on prescribed coordinates, and video monitoring of the basic subsystems of the telescope) and the auxiliary operations (evacuation, siderostat mirror unloading, and dome control).

Seasonal variability of the astronomical seeing on the Large Solar Vacuum Telescope

The results of optical measurements of the quality of astronomical seeing on the Large solar vacuum telescope (LSVT) in spring and summer are shown. It is noticed that in the summer measurements, the quality of vision is higher on average 2.5 times than in the spring. Information on the seasonal variability of the astronomical quality of vision can be useful in the planning of scientific experiments for the LSVT, as well as to improve the performance of existing adaptive system

Site selection for modern ground based large telescopes

The problem of selection of sites for modern telescopes which are characterized by favorable conditions for astronomical observations is discussed. A number of new sites to telescope construct with separate mountain peaks (above 2 km) as well as high image quality (astronomical seeing) and low level of cloud are pointed.