Atmospheric and Oceanic Optics最新文献

Smoky haze which occurs during large-scale wildfires essentially transforms the radiative regime of the atmosphere over large territories. The variability of shortwave radiation fluxes in a smoke-laden atmosphere is driven by variations in the optical and microphysical properties of smoke aerosols, including the spectral dependences of the imaginary part of the refractive index. These dependences are determined by the presence of black carbon, brown carbon, and radiation-selective absorbing organic compounds in aerosol particles. This study analyzes the aforementioned spectral dependences based on AERONET data during large-scale wildfires in Alaska in 2019 and Canada in 2023. The analysis includes the cases of extreme radiation absorption by black and brown carbon, where the imaginary part of the refractive index at a wavelength of 440 nm attained 0.50 and 0.27, respectively. Variations in the spectral dependence of the imaginary part of the refractive index under moderate manifestations of selective absorption of smoke aerosol during massive fires in Alaska and Canada are analyzed. Approximations for the spectral dependence of the imaginary part of the refractive index are suggested. The aerosol radiative forcing at the top of the atmosphere is estimated for the cases of extreme radiation absorption by black carbon and brown carbon in the visible and near-infrared spectral regions and of anomalous selective absorption. The results can be useful in monitoring of the radiative regime of the atmosphere and for the development of atmospheric remote sounding techniques.

Surface inspection under large strains is a critical problem for both civil and mechanical engineering. Optical techniques can be used for its solution. Digital image correlation (DIC) is one of these promising optical techniques; it is used to measure displacement and strain fields without contact with a surface under study. Input parameters can directly affect the strain field calculation accuracy. The correlation method is a key factor in DIC calculation of a strain field, especially under large strains. In this work, three spatial and incremental methods are tested; their accuracy and applicability are estimated; their advantages and drawbacks are discussed. The results can be useful for the developments of software for non-destructive testing.

А non-line-of-sight optical (NLOS) communication line with an unmanned aerial vehicle (UAV) through the water–atmosphere interface allows removing the limitation to the UAV position within the transmitter divergence angle during a communication session. However, the capabilities of such communication lines were not previously considered. We experimentally and theoretically estimate the capabilities of an NLOS optical communication line between an underwater transmission system and a flying UAV. Field experiments show a possibility of organizing stable NLOS optical communication at baseline distances of 90 m and UAV flight altitude of 30 m. The simulation of a communication line shows a useful signal to be mainly formed by radiation scattered in the atmosphere at short baseline distances and by radiation scattered in water at long baseline distances. Therefore, the useful signal is maximal at high water turbidity (Secchi depth is 3 m). The results make it possible to analyze the main patterns of generation of a useful signal in communication lines under study and can serve a basis for the creation of such systems.

A laser guide star (LGS) is an essential part of the adaptive optics system of a ground-based optical telescope. The main limitation of sodium LGSs, formed on the basis of the resonant fluorescence of mesospheric sodium atoms is low brightness. To estimate a possibility of creating LGS based on the fluorescence of other metals in the mesosphere, the efficiencies of fluorescence excitation schemes for atoms of potassium and nickel are calculated. The relative inverse fluorescence flux for transitions of potassium and nickel atoms is calculated taking into account the content of the atoms in the mesosphere and the transmittance of the atmosphere. The comparison with the results for sodium atoms is made. Our results can be used for the development of adaptive optics systems with artificial reference sources for ground-based telescopes and mesospheric lidars.

A laser guide star (LGS) is an essential part of the adaptive optics system of a ground-based optical telescope. The main limitation of sodium LGSs, formed on the basis of the resonant fluorescence of mesospheric sodium atoms is low brightness. To estimate a possibility of creating LGS based on the fluorescence of other metals in the mesosphere, the efficiency of fluorescence excitation schemes for iron atoms is calculated. The relative inverse fluorescence flux for transitions of iron atoms is calculated taking into account their content in the mesosphere and the transmittance of the atmosphere. The comparison with the results for sodium, nickel, and potassium atoms is made. Our results can be used for the development of adaptive optics systems with artificial reference sources for ground-based telescopes and mesospheric lidars.

It is shown that the development of the turbulence theory should aim at studying not only incompressible vortex component but also the adiabatic one, first of all, pressure and density fluctuations. The intensity of the pressure fluctuations in a turbulent flow is compared with fluctuations of the potentially available energy of Lagrangian particles. An equation linking the smoothing of entropy fluctuations with the generation rate of adiabatic fluctuations is proposed. The rate constant of entropy fluctuation smoothing is estimated from measurements in the atmospheric boundary layer. This constant allows one to relate the integral spatial scale of turbulent vortices to the standard deviation of the sound speed fluctuations in the atmospheric boundary layer. Estimates of the adiabatic noise amplitude in a turbulent medium are constructed and the relation between its energy and the correlation time of the vortex velocity fluctuations is shown.

Cirrus clouds are currently under close attention since they play an important role in the formation of the Earth’s climate. They are mainly studied through laser sounding of the atmosphere. The interpretation of laser sounding data requires an adequate optical model of cirrus clouds. However, most existing optical models are developed assuming a random spatial orientation of particles, which, according to recent experimental data, is often inaccurate. We suggest an optical model of cirrus clouds which considers the preferential horizontal orientation of particles within a cloud. The model includes ideal hexagonal plates and columns and hollow columns as quasi-horizontally oriented particles; it additionally incorporates hexagonal plates and columns, droxtalls and bullets, irregularly shaped particles, and aggregates of such particles as randomly oriented particles. The results are crucial for developing lidar data interpretation algorithms for studying cirrus clouds.

Microwave measurements of ozone were performed in the middle atmosphere over Apatity (67° N, 33° E) in winter 2022/2023, during a period of high solar activity in solar cycle 25, with the use of a mobile ozonometer with an operating frequency of 110.8 GHz. The device had a single-sideband noise temperature of 2500 K, which made it possible to measure variations in O₃ in the middle atmosphere with a 15-min resolution. The ozone vertical profiles at altitudes of 22–60 km were retrieved and compared with MLS/Aura satellite vertical profiles of ozone and temperature. The behavior of ozone in February–March 2023 is analyzed. Ozone variations took place during the sudden stratospheric warming (SSW) which occurred in mid-February and was accompanied by an extraordinary increase in the total ozone content (TOC) from 240 to 500 DU. The limits of ozone variations at altitudes of 25, 40, and 60 km are given. The effect of the strong geomagnetic disturbance (storm), which took place on March 23–24, on the daily variations in ozone at an altitude of 60 km is discussed.

Classification of atmospheric aerosols is significant in evaluating the influence of aerosols on the climate system, identifying aerosol sources, and improving aerosol satellite retrieval algorithms. There are different ways of classifying aerosol particles, but most of them do not take into account regional characteristics. We suggest an approach to classification of main aerosol types by the spectral values of aerosol optical depth by the method of k-medians based on archival AERONET photometric observations in the Middle Urals. The spectral values of extinction coefficients calculated with the use of MOPSMAP software from data of MUrA regional aerosol model and CALIPSO global model were defined as initial centers of clusters. Five aerosol types were identified: dust, clean continental (background), polluted continental/smoke, polluted dust, and elevated smoke. The analysis of data for 2004–2012 has shown clean continental and dust aerosols to be most common in the Middle Urals (26 and 25% of observations, respectively), and the percentage of polluted continental/smoke aerosol to be 20%. The suggested approach makes it possible to determine the predominant aerosol type at an observation site, thus significantly supplementing the information received by ground-based spectral photometric measurements.

The range of detecting objects in inhomogeneous optical radiation propagation media by television measuring systems decreases under the effect of backscattering interference (BI). Active-pulse television measuring systems (AP TMS) enables suppressing a significant part of BI. However, the residual effect on the range measurement accuracy requires estimation. The paper estimates the BI effect on the forms of range measuring functions of AP TMS. Methods for retrieving the form of the AP TMS range measuring function in turbid media have been developed. To minimize the BI effect, a method of calculating and subtracting coefficients and a method of removing the constant component of a spectrum are suggested. The proposed methods were tested with 30 experimental video records obtained in a Large Aerosol Chamber (LAC) of V.E. Zuev Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, for two multiarea range measurement methods and five meteorological media. The best result was achieved when applying the method of calculating and subtracting coefficients to video records when AP TMS operated in the multiarea range measuring mode: the SD was reduced by 4.5 times on average.