Increase In Optical Thickness Research Articles

Development of the method of remote sensing of low-concentration gases of the atmosphere taking into account the humidity fluctuations of the air

The emergence of strong desert vortices covering large areas, including the areas of large cities with dense population, the need to quickly obtain sufficient information on the state of desert ecosystems in large areas makes the application of remote sensing methods an urgent issue. At present, the method of measuring the desert aerosol using scattered solar radiation has been proposed, and the method of measuring the optical thickness of the dust aerosol has been substantiated. A new method of optimization of remote sensing systems and information-measurement systems in general is proposed in the article. A method of remote determination of aerosol optical thickness increase, which involves measuring the scattered radiation of the sun, has been proposed. The main goal of the study is to develop a remote sensing method that allows determining the dynamics and cause of the increase in aerosol optical thickness. The scientific novelty of the work is a new method that is invariant to the variations of the aerosol optical thickness under the influence of hydration and dehydration processes. By using the proposed three-wave biparametric Sun photometer, the effect of aerosol hygroscopic growth on the measurement results is eliminated.The given critical assessment of the state of atmospheric pollution monitoring and the consideration of the main shortcomings of the aerosol pollution monitoring carried out in the country will allow further improvement of such monitoring in the future. The proposed remote sensing method for determining the dynamics of aerosol optical thickness growth allows to determine the origin of aerosol optical thickness growth by measuring scattered solar radiation at two different wavelengths and in two optical air masses.

Study of polarization transmission characteristics in nonspherical media

In order to deal with the problem of serious pollution caused by non-spherical particles, this study developed and obtained a non-spherical medium based on the theoretical basis of polarized optics and a new non-spherical particle preparation method (burning Ganoderma lucidum spores method). A polarized light simulation transport model based on the T-matrix was established by applying it to the smoke simulation environment. Using this polarization transmission model, simulation experiments were conducted to determine the effects of wavelength, polarization state, optical thickness and various transmission media on the Degree of Polarization (DOP). The simulation results show that both incoming linearly and circularly polarized light undergo depolarization as the optical thickness increases; however, the depolarization of circularly polarized light becomes more severe. In addition, the DOP in the non-spherical particle medium is always larger than that in the spherical particle medium, which indicates that the circularly polarized light is superior to the linearly polarized light in terms of deflection precession.

Analysis of the effect of optical thickness on polarization in a sea fog stratified environment.

Since there are usually multiple layers present in a real-world sea fog environment, and because previous studies have tended to analyze sea fog as a single layer rather than as refined layered sea fog, this paper splits sea fog into two categories: water fog and salt fog double-layer environments. By adjusting the optical thickness of the two layers of media, we may investigate the issue of the law governing the transmission of polarized light. In this paper, the analysis is mainly carried out through a simulation and experimental tests. The simulation portion is based mostly on the improved layered Monte Carlo approach, which builds a simulation model more appropriate for multilayer non-spherical media by using the accumulation principle to determine the scattering and transmission properties between layers. The tests are conducted by altering the double-layer medium's optical thickness, incoming wavelength, and polarization state, and then getting the polarization information of visible light after transmission through the complicated environment. The findings demonstrate that the optical thickness of the sea fog double-layer media affects polarized light transmission in a non-negligible way. Longer wavelength polarized light may keep polarization information better as the optical thickness increases, and circularly polarized light has polarization-preserving properties that are superior to linearly polarized light. By contrasting the simulation findings with the experimental data, the consistency of the two conclusions is confirmed, and the study offers a helpful resource for the transmission of polarized light in the sea fog environment.

Revisit interior penalty based diffusion synthetic acceleration for the SN transport equation discretized with discontinuous Galerkin method

Diffusion Synthetic Acceleration (DSA) techniques based on symmetric and nonsymmetric versions of the Interior Penalty (IP) method have been proposed to accelerate the scattering source iteration of the SN transport equation discretized with discontinuous Galerkin (DG) method in the previous researches. The performances of DSA based on various IP methods need to be compared comprehensively. The Robin boundary condition is usually adopted to treat the vacuum boundaries in solving the diffusion equation of DSA, but in the thick diffusive limit, the Dirichlet boundary condition was derived for the diffusion equation to give the correct leading-order interior solution. The influence of the boundary condition for the vacuum boundaries in DSA needs to be analyzed. In this study, the DSA schemes with three various IP methods (SIP, IIP and NIP) in conjunction with Krylov iterative method are summarized in a complete view, and the approaches to dealing with the instability problem of DSA in the optically thick and nearly voided regimes are discussed. From the numerical experiments, it suggests that the DSA schemes with IIP, NIP and SIP perform closely to each other, and there is no specific IP method which shows advantages over the others under any conditions. With other conditions fixed, the performance of the DSA scheme with the Dirichlet boundary condition becomes better than that with the Robin boundary condition with the increase of optical cell thickness. There is no apparent relationship between the performance of the DSA scheme and the discretization order of DG.

Case A or Case B? The Effective Recombination Coefficient in Gas Clouds of Arbitrary Optical Thickness

In calculations of the ionization state, one is often forced to choose between the Case A recombination coefficient α A (sum over recombinations to all hydrogen states) or the Case B recombination coefficient α B (sum over all hydrogen states except the ground state). If the cloud is optically thick to ionizing photons, α B is usually adopted on the basis of the “on-the-spot” approximation, wherein recombinations to the ground state are ignored because they produce ionizing photons absorbed nearby. In the opposite case of an optically thin cloud, one would expect the Case A recombination coefficient to better describe the effective recombination rate in the cloud. In this paper, I derive an analytical expression for the effective recombination coefficient in a gas cloud of arbitrary optical thickness which transitions from α A to α B as the optical thickness increases. The results can be readily implemented in numerical simulations and semi-analytical calculations.

Simulation of Pulverized Coal Combustion Process Considering Turbulence-Radiation Interaction.

In this paper, the combustion process of a 350 MW opposite pulverized coal combustion boiler is studied using a combined field test and numerical simulation. Considering the turbulence-radiation interaction (TRI) effect caused by turbulent particle pulsation during the combustion process, the TRI model is modified by introducing optical factors. The interaction between the optical thickness and the radiation pulsation of pulverized coal particles during the combustion process is studied to learn the influences of turbulent particle combustion on radiative heat transfer. According to the analysis of the TRI influence on pulverized coal combustion, the temperature of the cross section decreases with TRI. Compared with the traditional radiation model calculation, the time-average temperature of the cross section is reduced by 49.85 K, and the deviation from the experimental data is reduced by 1.54%. It is proved that the temperature distribution in the furnace considering TRI is closer to reality. In the numerical simulation of the TRI sensitivity to the optical thickness of the particles, it is found that with TRI, the increase of optical thickness will strengthen the effect of turbulent kinetic energy in the combustion area. Due to the increase in particle density, the content of the main radiation medium produced by combustion, H2O and CO2, increases and the radiation effect in the furnace is enhanced. In the fire area with dense particles, the average temperature of the cross section increases by 28 K. Hence, the change in optical thickness causes the change of TRI parameters, and the TRI effect becomes more significant with the increase of particle load.

Investigation on the radiation heat transfer in dilution zone of a 100 kWth oxy-fuel pressurized circulating fluidized bed

Due to high pressure, complicated flue gas components and high particle concentration in dilute phase region, radiation heat transfer in the oxy-fuel combustion pressurized circulating fluidized bed (PCFB) is complex. To indicate the radiation heat transfer, both experiments and numerical simulations were carried out, where the Computational Fluid Dynamics (CFD) modelling was based on the full spectrum correlated k-distribution model (FSCK) combined with Mie theory. The multiphase flow behaviors, combustion reactions and radiation heat transfer of the PCFB under oxy-fuel combustion at 0.6 MPa were revealed with good agreement between the simulated result and the experimental data. The predictions of radiation heat transfer were accomplished under different oxygen concentration and operating pressure. The results illustrated that the existence and accumulation of particles lead to the increase of flue gas optical thickness, which hinders more radiation energy transmitted to the wall. Various oxygen concentration leads to the different distribution of temperature and radiative medium concentration, which all have an impact on total radiation intensity. Compared with temperature, particle radiation and gas radiation have less effect on radiation heat transfer under different atmosphere. In addition, the operating pressure affected the flue gas temperature as well as particle concentration and radiative gas concentration in the dilution zone, and the combustion atmosphere also has an influence on the above characteristics. Complicated thermodynamic states lead to dissimilar thermal radiation characteristics under different operating condition.

Physical-Optical Properties of Marine Aerosols over the South China Sea: Shipboard Measurements and MERRA-2 Reanalysis

Aerosols play an important role in the Earth–atmosphere system. Their impacts on the weather and climate are highly dependent on spatiotemporal distributions as well as physical-optical properties. Physical-optical properties of the aerosols over the Asian continent have been widely investigated, but there are relatively few observations in maritime locations, especially the South China Sea (SCS). Here, with the combination of in situ ship-based observations from June and July 2019 as well as long-term MERRA-2 reanalysis datasets from January 2012 to December 2021, the physical and optical properties of marine aerosols in the SCS are explored. The impacts of meteorological factors, particularly frontal systems, on the aerosol properties are further analyzed based on detailed observations. The observed results show that aerosols are vertically concentrated below 3 km and the extinction coefficient reaches the maximum value of 0.055 km−1 near 480 m. Moreover, the particles are composed of an accumulation and a coarse particle mode, and they conform to the lognormal distribution. The synoptic-scale case study demonstrates that both the cold front and stationary front lead to an increase in aerosol optical thickness (AOD), which is due to the enhanced wind speed and the hygroscopic growth of fine particles, respectively. The long-term analysis indicates that AOD decreases from northwest to southeast with the increasing distance away from the continent, and it reflects higher values in spring and winter than in summer and autumn. Sulfate and sea salt dominate AOD in this region when compared with other components. The overall AOD shows a significant negative trend of −0.0027 year−1. This work will help us further understand the physical and optical properties of marine aerosols over the SCS and then contribute to quantifying the aerosol radiative forcing in the future.

The Research of Long-Optical-Path Visible Laser Polarization Characteristics in Smoke Environment

The concentration of smoke in an environment can cause obvious interference to visible light intensity imaging, and it is a non-negligible factor in the polarized imaging of ground-based targets. Smoke particles cause severe scattering of photon intensity, resulting in polarization. In this case, low-visibility targets can be effectively identified by detecting the polarization dimension of targets. However, the polarization transmission of smoke in an environment is unclear, and the theoretical simulation lacks experimental reliability verification. To study this problem, this study constructs a polarization transmission model in a smoke environment and simulates and analyzes the scattering of visible polarized light at 450, 532, and 671 nm under different smoke densities. The optical thickness is determined to establish a reliable connection between the simulation and the external field long optical path test and verify the transmission of polarized light. Results show that the method has a 60% confidence in the polarization transmission model. With the increase in optical thickness, the degree of polarization (DOP) of the three wavelengths in the visible light band decreases, and the DOP of each polarized light decreases. No obvious difference is found between the DOPs of circularly polarized light at 450 nm and linearly polarized light. The DOP of circularly polarized light at 532 nm is 1–5% higher than that of linearly polarized light, 1–10% higher than that of the outdoor test, 1–5% higher than that of circularly polarized light at 671 nm, and 2–15% higher than that of the outdoor test. Therefore, the shorter the wavelength in the visible band, the higher the DOP. With the increase in wavelength, the polarization characteristics of circularly polarized light are gradually better than those of linearly polarized light.

Effects of diffuse and collimated beam radiation on a symmetrical cooling case of natural convection

In any scenario of heat transfer in fluid medium, all modes, i.e., conduction, convection and radiation are present. Further, the radiation heat transfer may be diffuse (propagation of energy in all directions) or collimated (energy propagates in single direction). The qualitative and quantitative analysis of radiation heat transfer are required in order to understand its effects on the fluid flow and also on heat transfer. In the present work, the effects of diffuse and collimated radiation on the symmetrical cooling case of natural convection in a two-dimensional cavity heated from the bottom have been investigated, numerically. The cavity is convectively heated from the bottom, while both vertical walls of the cavity are isothermal. The top wall is adiabatic and all walls are opaque for radiation heat transfer. For the collimated case, a small semitransparent window has been created on the left wall and collimated irradiation of value 1000 W/m2 at an azimuthal angle 135°is applied on this semitransparent window. The study has been performed in two stages, first, the effect of diffuse radiation on the natural convection has been observed and then, in the second stage, a collimated beam is passed through the semitransparent window. The results reveal that the diffuse radiation has little effect on the dynamics of two rolls inside the cavity, however, collimated beam irradiation changes the dynamics of two rolls significantly and also the heat transfer characteristics. This further changes with the optical thickness of the fluid. The left vortex is bigger than the right vortex for collimated beam in transparent fluid, whereas, a reverse trend is seen for the collimated beam for the non-zero optical thickness of the fluid. The size of the left vortex increases with the increase of optical thickness of the fluid. The heat transfer reversal happens at the zone of a collimated beam incident on the bottom wall for transparent medium, whereas, this does not happen for participating medium. Further, this study helps in understanding the heat transfer in a room, fluid flow in shallow water lakes affecting aquatic life etc., due to solar radiation.

Impact of Atmospheric Optical Properties on Net Ecosystem Productivity of Peatland in Poland

Peatlands play an important role in the global carbon cycle due to the high carbon storage in the substrate. Ecosystem production depends, for example, on the solar energy amount that reaches the vegetation, however the diffuse component of this flux can substantially increase ecosystem net productivity. This phenomenon is observed in different ecosystems, but the study of the atmosphere optical properties on peatland production is lacking. In this paper, the presented methodology allowed us to disentangle the diffuse radiation impact on the net ecosystem production (NEP) of Rzecin peatland, Poland. It allowed us to assess the impact of the atmospheric scattering process determined by the aerosol presence in the air mass. An application of atmospheric radiation transfer (ART) and ecosystem production (EP) models showed that the increase of aerosol optical thickness from 0.09 to 0.17 caused NEP to rise by 3.4–5.7%. An increase of the diffusion index (DI) by 0.1 resulted in an NEP increase of 6.1–42.3%, while a DI decrease of 0.1 determined an NEP reduction of −49.0 to −10.5%. These results show that low peatland vegetation responds to changes in light scattering. This phenomenon should be taken into account when calculating the global CO2 uptake estimation of such ecosystems.

The influence of target surface position on plasma characteristics in dual-pulse fiber-optic laser-induced breakdown spectroscopy

Laser-produced plasmas of dual-pulse fiber-optic laser-induced breakdown spectroscopy with different target positions relative to the waist region of laser focusing are studied using fast imaging and optical emission spectroscopy (OES). The laser energy of the two laser pulses is both maintained at around 18 mJ (i.e. the total energy is 36 mJ). The inter-pulse delay is kept at 250 ns. Ten spot sizes changing from 947 to 543 μm are obtained by precisely adjusting the distance between the focusing lens and the target surface. The profile of laser beam output from fiber shows a distinct top-hat shape. When approaching the dual-pulse waist region, the self-absorption and self-reversal of matrix iron lines gradually become intense while the plasma emission is enhanced, but the signal-to-noise ratio of minor elements gradually decreases. Under a similar spot size, the emission intensity with the target surface behind the waist region is weaker than that in front of the waist region and also with greater jitters. The target surface position is optimized to deviate from the waist region by ~ 1.3–1.6 mm towards the focusing lens for improving SNR of minor elements, corresponding to the lens-to-sample distances of 11.8–12.1 mm. Plasma morphology has undergone a transformation from stream- to umbrella-like structure using the recorded Intensified Charge-Coupled Device (ICCD) images. The expansion distance of the plasma front is increased from 1.07 to 1.28 mm, and the plasma volume is increased from 0.59 to 1.60 mm3. Besides, by utilization of OES, the maximum variation of plasma temperature and line broadening width rise to 2702 K from 1630 and to 0.0492 from 0.0316 nm along the vertical direction. The significant increase of optical thickness and nonuniformity of plasma temperature and density is the main reason for the intensification of self-absorption.

Clouds damp the radiative impacts of polar sea ice loss

Abstract. Clouds play an important role in the climate system: (1) cooling Earth by reflecting incoming sunlight to space and (2) warming Earth by reducing thermal energy loss to space. Cloud radiative effects are especially important in polar regions and have the potential to significantly alter the impact of sea ice decline on the surface radiation budget. Using CERES (Clouds and the Earth's Radiant Energy System) data and 32 CMIP5 (Coupled Model Intercomparison Project) climate models, we quantify the influence of polar clouds on the radiative impact of polar sea ice variability. Our results show that the cloud short-wave cooling effect strongly influences the impact of sea ice variability on the surface radiation budget and does so in a counter-intuitive manner over the polar seas: years with less sea ice and a larger net surface radiative flux show a more negative cloud radiative effect. Our results indicate that 66±2% of this change in the net cloud radiative effect is due to the reduction in surface albedo and that the remaining 34±1 % is due to an increase in cloud cover and optical thickness. The overall cloud radiative damping effect is 56±2 % over the Antarctic and 47±3 % over the Arctic. Thus, present-day cloud properties significantly reduce the net radiative impact of sea ice loss on the Arctic and Antarctic surface radiation budgets. As a result, climate models must accurately represent present-day polar cloud properties in order to capture the surface radiation budget impact of polar sea ice loss and thus the surface albedo feedback.

Effect of laser beam on depolarization characteristics of backscattered light in discrete random media

When lidar is used to detect the microphysical properties of clouds and aerosols, it is a spot when the laser reaches the clouds. This is because the lidar has a certain divergence angle, and the location of the lidar is at a certain distance from the clouds. In this paper, a Monte Carlo method for simulating multiple scattering in clouds by lidar is presented, and the influence of the size and shape of the spot on the backscattering of polarized light in clouds is analyzed. From the calculation results, it can be seen that the spot will increase the depolarization ratio of lidar, and the larger of the size of the spot, the larger the depolarization ratio. In addition, depolarization ratio increases with the increase of optical thickness and field of view angle. The methods and conclusions in this paper are of great significance for long-distance detection of discrete random media by laser.

Computation and Comparison of Cloud Infrared Radiation Characteristics

Abstract Cloud is a common weather phenomenon in the sky. It is formed by condensation of water vapor in the atmosphere. It is a suspension composed of water droplets, ice crystals or their mixtures. The infrared radiation characteristics of clouds are related to the particles phase state in clouds, the particle radius distribution and the cloud optical thickness. They are also affected by the sun, earth surface types and atmospheric conditions. In this paper, it introduces the physical parameters of the ice crystals in cloud, and researches the scattering characteristics of ice crystals. Based on radiation transfer algorithms, an ice cloud radiation model is established. The ice cloud infrared radiation is analyzed that the ice clouds infrared radiation varies with optical thickness. It shows that when the cloud optical thickness is not large, the radiance of ice clouds decreases with the increase of optical thickness.

Variations of atmospheric aerosol parameters in periods of seismic activity in Tien–Shan

Combination of numerical modeling (MERRA) and ground based (AERONET) monitoring of atmospheric aerosol parameters were used to discover a possible connection to seismic activities within the territory of Tien-Shan. The obtained results demonstrated consistent behavior between increase of aerosol optical thickness (AOT) and powerful earthquakes, epicenters of which were located within 200 km from the “Issyk-Kul” station (AERONET). Thereat, the dominant role was played by fine-dispersed particles, which virtually determined the nature of AOT evolution. We also observed well-defined changes of the ratio between mass fraction PM1.0 (particles less than 1.0 μm aerodynamic diameter) and optical thickness of aerosol scattering several days before an earthquake of M > 5.0 magnitude.

Spatiotemporal distributions of cloud radiative forcing and response to cloud parameters over the Mongolian Plateau during 2003–2017

AbstractThe Mongolian Plateau (MP) is among the most sensitive areas to global climate change, and the clouds over the MP have a greater impact on regional and global radiation budgets by altering the atmospheric and surface radiative forcing. In this study, daily Cloud and Earth Radiation Energy System data are used to investigate spatiotemporal variation of cloud radiative forcing (CRF) at the top of atmosphere (TOA), surface and atmosphere over the MP from 2003 to 2017 and then combined with Moderate Resolution Imaging Spectroradiometer level 2 atmospheric data during the same period to analyse the cloud parameter impacts on CRF over the MP. At the TOA and surface, net radiative forcing (NRF) and shortwave radiative forcing (SRF) have cooling effects and longwave radiative forcing (LRF) have heating effects in all four seasons, and the NRF cooling effect in most areas of the MP decreases in summer and autumn and increases in spring and winter. In the atmosphere, SRF in spring and summer and NRF in summer reach larger values and heat the atmosphere, and LRF plays a strong cooling role in winter. The NRF change trend in the atmosphere over Mongolia is noteworthy in spring, its reduction slope is large, and most areas of Mongolia passed a significance test. As expected, a significant negative correlation was observed between cloud cover and NRF (as well as SRF) at the TOA and surface and a positive correlation was observed with NRF/SRF in the atmosphere and all LRF. With the increase in cloud optical thickness and cloud water path, the NRF and SRF cooling effects at the TOA and surface, the LRF cooling effect in the atmosphere, the LRF heating effect at the surface, and the SRF heating effect in the atmosphere all become stronger.

Impact of Mixed Convective and Radiative Heat Transfer in Spiral-Coiled Tubes

Abstract Spiral-coiled tube heat exchangers (SCTHE) have higher heat transfer as compared to the conventional heat transfer devices and are extensively used to extract heat from exhaust gases in the chemical processing industries and also from sunlight for domestic applications. However, no attention has been made to predict heat transfer characteristics considering combined convective and radiative heat transfer in spiral-coiled tubes. In the present study, numerical analysis has been performed to predict fluid flow and heat transfer characteristics by combined forced convection and thermal radiation in spiral-coiled tubes. The P-1 radiation and the renormalized group (RNG) k–ε turbulence models have been used to study the effect of thermal radiation and turbulent convection heat transfer in the spiral-coiled tube, respectively, over a wide range of Reynolds numbers (10,000–100,000) and curvature ratios (0.02–0.05). The emissivity and optical thickness have been varied from 0.0 to 1.0 and 0.0 to 8.0, respectively, to investigate the effect of thermal radiation on heat transfer characteristics in spiral-coiled tubes. For the considered Reynolds number range, it is found that the heat transfer is enhanced by approximately 10% when radiation is taken into account. It is found that the heat capacity increased with an increase in optical thickness and wall emissivity. Further, the effect of optical thickness on fully developed flow is observed weak and the average heat transfer coefficient is influenced by the wall emissivity over the entire flow.

Evaluation of Cloud Top Height Retrievals from China’s Next-Generation Geostationary Meteorological Satellite FY-4A

To evaluate the validity of cloud top height (CTH) retrievals from FY-4A, the first of China’s next-generation geostationary meteorological satellite series, the retrievals are compared to those from Himawari-8, CloudSat, Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), and Moderate Resolution Imaging Spectroradiometer (MODIS) operational products from August to October 2017. Regarding CTHs from CloudSat, CALIPSO, and MODIS as truth, the results show that the performance of FY-4A CTH retrievals is similar to that of Himawari-8. Both FY-4A and Himawari-8 retrieve reasonable CTH values for single-layer clouds, but perform poorly for multi-layer clouds. The mean bias error (MBE) shows that the mean value of FY-4A CTH retrievals is smaller than that of Himawari-8 for single-layer clouds but larger for multi-layer clouds. For ice crystal clouds, both FY-4A and Himawari-8 obtain the underestimated CTHs. However, there is a tendency for FY-4A and Himawari-8 to overestimate the CTH values of CloudSat and CALIPSO mainly for low level liquid water clouds. The temperature inversion near the tops of water clouds may result in an overestimation of CTHs. According to the MBE change with altitude, FY-4A and Himawari-8 overestimate the CTHs mainly for clouds below 3 km, and the overestimation is slightly more apparent in Himawari-8 data than that in FY-4A values. As the cloud optical thickness (COT) increases, the CTH bias of FY-4A CTH retrievals gradually decreases. Two typical cases are analyzed to illustrate the differences between different satellites’ CTH retrievals in detail.

Some observational manifestations of the periodic inhomogeneity of absorbing and scattering atmospheres

We consider frequency and directional features of the reflectance and transmittance of an inhomogeneous scattering and absorbing atmosphere with the scattering albedo periodically varying with depth. The dependence of global optical properties of such media on optical thickness is found. Two different kind of problems are considered dependent on that by monochromatic or continuum, mono-directional or diffuse radiation illuminate the medium. The numerical results show how the observed intensities and line-profiles respond to the medium inhomogeneity with an uniform increase in optical thickness. Astrophysical aspects of these features are discussed.