Vol 31, No 6 (2018)

The coherence length and possible broadening of a laser beam in the atmospheric boundary layer under the effect of random inhomogeneities of the refractive index are estimated from experimental data of remote acoustic sounding. The possibility of significant loss of coherence and noticeable broadening of the laser beam due to turbulence in nighttime are noted.

Н₂О and СО₂ continuum absorption within the IR absorption bands depends on the frequency boundaries within which the local line contribution is accounted for. Correlation between the maximal value of this boundary and the line shape at large frequency detuning is observed for the 4.3-, 2.7-, 1.4-, and 1.2-μm СО₂ bands, as well as for rotational and 1400–1900-, 3500–3900-, and 5200–5500-cm⁻¹ Н₂О bands. The continuum absorption can be unambiguously determined from measurements in the band wings if one assumes that it is purely continual there. Within bands, the continuum absorption cannot be determined unambiguously and depends on the local line contribution boundary chosen.

It is found that the reflection coefficient of multilayer dielectric mirrors strongly depends on the medium (gas) humidity. This effect can result in both an increase and decrease in the reflection coefficient, which is determined by a change in the refractive indices of the dielectric layers (when filling with water vapor). The mirror reflection coefficient can increase up to 0.9% in a gas with the humidity close to the dew point. Changes in the reflection coefficient of a mirror in gaseous media which contain different water vapor isotopes (H₂¹⁶O, H₂¹⁸O, and D₂O) are studied. Mirrors of a CRDS spectrometer with the reflection coefficient R = 0.9999 are studied and the upper bound of the variation in the reflection coefficient versus air humidity is estimated.

Coherent properties of nondiffracting pseudo-Bessel optical beams propagating in a turbulent atmosphere are studied theoretically. The solution of the equation formulated based on the paraxial approximation of the scalar wave equation for the second-order transverse mutual coherence function of the optical radiation field is analyzed. The behavior of the modulus and phase of the complex degree of coherence, coherence radius, and integral scale of the coherence degree of the Bessel-Gaussian optical beam and conical optical wave obtained by cone focusing of the optical beam by an axicon is studied as a function of optical beam parameters and characteristics of a turbulent atmosphere. Significant qualitative and quantitative distinctions between the studied coherence characteristics for cases of a Bessel-Gaussian optical beam and conical optical wave have been revealed. In general, under similar conditions of propagation in a turbulent atmosphere, the coherence of a conical optical wave is higher than that of a Bessel-Gaussian optical beam.

The parameters are presented for the scattering phase functions measured in the northern part of the tropical Atlantic. The interrelation is considered between the parameters of the scattering functions and water dynamics. We present the scattering phase functions measured in waters of the main currents and in the regions of water upwelling and downwelling. The limiting values of the parameters of the scattering phase functions observed are presented. The interrelation is determined between the asymmetry factor of scattering phase functions and the scattering coefficient. The parameters of this interrelation measured in upwelling differ from those for the other waters in the experimental area. The interrelation is determined between the scattering and extinction coefficients.

The concept of nonstationary diffraction-beam optics of high-power femtosecond laser pulses is presented. According to the concept, the power of a beam propagates along specific light structures—diffraction- beam tubes. These tubes do not intersect and do not exchange energy, but changes in their shape and cross sections during propagation show the effect of physical processes that occur with radiation in the medium. The nonstationary theory is supplemented with evolutionary equations for time-averaged diffraction rays and effective squared radii of diffraction tubes.

Data from aircraft and satellite sensing at the ocean–land boundary in the region of the Kara Sea in October 2014 are compared, using 11 and 7 profiles, which were synchronously measured over a continental part and ocean, respectively. It was found that the satellite usually overestimates the CH₄ and CO₂ concentrations in the 0–8-km layer over the continental part of the Arctic region and underestimates them over the ocean. Over continent, the satellite overestimates the methane concentrations by 28 ppb in the boundary layer and by much more in the middle (182 ppb) and upper (113 ppb) troposphere. Over ocean, the satellite measurements are, on average, lower by 37 ppb in the boundary layer, by 73 ppb in the middle troposphere, and by 71 ppb in the upper troposphere. Over continent, the discrepancy in CO₂ concentrations, measured with different instruments, is, on average, 18.2 ppm in the boundary layer and can vary from 3.2 to 26.5 ppm. In the middle troposphere (4 km), the average differences decrease to 10.8 ppm, with the range of differences even increasing somewhat, to 0.6–25.5 ppm. In the upper troposphere (8 km), the average difference in measurements between the instruments decreases to 2.8 ppm. The underestimation turns out to be greater in amplitude over the ocean. It is noteworthy that the comparison yielded acceptable results for CO and O₃.

The measurements with a CIMEL CE 318 sun photometer near St. Petersburg within the AERONET international monitoring network are analyzed. Typical regional aerosol optical parameters (aerosol optical depth, Angstrom exponent, and single scattering albedo) and their variations are determined. Certain regularities in variations in the aerosol parameters over the northwest region of the Russian Federation are revealed. The study is supplemented by the joint analysis of data from the nearby AERONET observation sites in Finland and Estonia, satellite measurements, and MERRA reanalysis data.

Atmospheric changes in the lower troposphere have been remotely studied using a self-engineered Mie scattering lidar with special emphasis on aerosols and clouds profiling over Islamabad region in Pakistan. The lidar is based on a Nd:YAG laser operating at 1064 nm, with maximal energy of 350 mJ at 20-Hz repetition rate and 5-ns pulse length. A silicon avalanche photodiode (Si-APD, C30950E) module is used as a detector. A higher resolution of the lidar revealed time evolution of thermal transport phenomena in the convective boundary layer. Regions of incessant wind speed, temperature, and particulates concentration have been detected through band-like structures at altitudes above 900 m. Strong backscattering (β) and extinction (α) due to a partially invisible thin cloud layer falling in the field-of-view of the lidar beyond 4 km have been identified.

We analyze the dynamics of layer-by-layer variations in aerosol contamination of snow cover under the circulation conditions during winter at the site of the Fonovaya Observatory (Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences) in the Tom-Ob interfluve. The chemical composition of the snow cover at the observation point is characterized. It is found that in the elemental composition of the aerosol substance accumulated in the snow cover, a typomorphic association of indicator elements associated with coal mining is consistently manifested. The conclusion is geochemically substantiated that enterprises of the coal-mining industry, located southward of the region under study, have a seasonal effect on the aerosol field of the Fonovaya Observatory. It is shown that the remote sources of aerosol contamination of the snow cover should be identified through the morphometric analysis of the terrain and a retrospective estimation of temporal variability of the indices, reflecting the effect of meteorological factors (ratios of dispersion fractions of near-surface aerosol, wind regime, snowfall intensity), and in the context of specific features of the layer-by-layer distribution of indicator groups of typomorphic elements in the snow layer that characterize the specific types of industrial plants.

The intensity variation of 557.7 nm oxygen green line and 630.0 nm oxygen red line at Kiso observatory, Tokyo, and variations in critical frequency of the ionospheric F2 layer (foF2) and semi transparency coefficient related to the E layer before earthquakes with magnitude ≥ 5 are considered for 1979 to 1990. The intensity of both the lines increases within six days before earthquakes; foF2 and semi transparency coefficient abnormally increase before enhancement of airglow. The superposed epoch analysis of each variable is done for further confirmation. Some physical processes in atmosphere-ionosphere in pre-seismic days enhance the concentration of electron and neutral molecules in the ionospheric F and E regions. These events influence the dissociative recombination processes related to oxygen emission, and so the intensity of two line emissions show some special type of variations during earthquake events.

The performance of a direct variational data assimilation algorithm with quasi-independent data assimilation at individual steps of the splitting scheme has been studied in a realistic scenario of air pollution assessment in the city of Novosibirsk by monitoring system data. For operation under conditions of a sparse monitoring network, an algorithm with minimization of the spatial derivative of the uncertainty (control) function adjusted to data assimilation is proposed. The use of the spatial derivative minimization increases the smoothness of the uncertainty (control functions) reconstructed, which has a positive effect on the reconstruction quality in the scenario considered.

Requirements are determined for the spontaneous Raman lidar transceiver system, designed for solving problems dealing with studying the atmospheric boundary layer and predicting dangerous smog situations. The optical scheme of a lidar transceiver system with a narrow field of view and minimal dead zone is synthesized. The results of computer simulation of the lidar overlap functions obtained by the ray tracing method for few optical schemes of the receiving optical system are presented. It is shown that when a multielement transceiver based on a combination of four receiving apertures of different diameters is used, a lidar sensing range can be from 5 to 3000 m for the dynamic range of the lidar response of no more than 10.

A lidar complex designed at V.E. Zuev Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences (Tomsk) and used at the Siberian Lidar Station (56.5° N, 85.0° W) for the study of ozone dynamics near tropopause and for tracking global ozonosphere changes is presented. It allows measurements of ozone vertical distribution in the upper troposphere–stratosphere when sounding using the differential absorption technique at the wavelength pairs 299/341 and 308/353 nm. The lidar complex covers altitudes from ∼5 to ∼45 km.

Features of a two-mirror adaptive system for correction of atmospheric disturbances of the Large Solar Vacuum Telescope are described. The system has been developed with allowance for the correction of instrumental vibrations of the telescope in a wide amplitude-frequency range, with an open siderostat supply mirror. The light wavefront tilt and its deformations are corrected separately. The adaptive optics system is designed to work with extended light sources (the Sun), with low-contrast image details.

Possible versions of sensors based on the pseudoreversal of the wavefront of the measuring beam and photoelectronic–optical amplification of the angular misalignment signal are considered. Estimation of the sensor parameters suggests the possibility of creating measuring systems that meet the requirements of the Millimetron telescope.