Distribution Of Extinction Coefficient Research Articles

Label-free superior contrast with c-band ultra-violet extinction microscopy

In 1934, Frits Zernike demonstrated that it is possible to exploit the sample’s refractive index to obtain superior contrast images of biological cells. The refractive index contrast of a cell surrounded by media yields a change in the phase and intensity of the transmitted light wave. This change can be due to either scattering or absorption caused by the sample. Most cells are transparent at visible wavelengths, which means the imaginary component of their complex refractive index, also known as extinction coefficient k, is close to zero. Here, we explore the use of c-band ultra-violet (UVC) light for high-contrast high-resolution label-free microscopy, as k is naturally substantially higher in the UVC than at visible wavelengths. Using differential phase contrast illumination and associated processing, we achieve a 7- to 300-fold improvement in contrast compared to visible-wavelength and UVA differential interference contrast microscopy or holotomography, and quantify the extinction coefficient distribution within liver sinusoidal endothelial cells. With a resolution down to 215 nm, we are, for the first time in a far-field label-free method, able to image individual fenestrations within their sieve plates which normally requires electron or fluorescence superresolution microscopy. UVC illumination also matches the excitation peak of intrinsically fluorescent proteins and amino acids and thus allows us to utilize autofluorescence as an independent imaging modality on the same setup.

Impact of CALIPSO profile data assimilation on 3-D aerosol improvement in a size-resolved aerosol model

Based on the three-dimensional variational assimilation (3DVAR) algorithm, the extinction coefficient profiles of the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite were assimilated for the first time on the basis of the aerosol variables from the Model for Simulating Aerosol Interactions and Chemistry (MOSAIC) mechanism of the Weather Research and Forecasting-Chemistry (WRF-Chem) model. A light aerosol pollution episode (case1) and a heavy pollution event (case2) were selected to simulate and predict using the WRF-Chem model. Two sets of data were assimilated: CALIPSO derived aerosol extinction coefficient profiles and surface PM mass concentration data obtained from ground monitoring stations across China. Then, various aerosol data sources including ground-based lidar in Beijing area, Himawari-8 (H-8) satellite aerosol optical depth (AOD) and surface PM monitors were used for comprehensive evaluate the impact of CALIPSO data assimilation on the model performance. The results showed that simultaneous assimilation of the CALIPSO extinction coefficient profiles and surface PM mass concentration data can effectively improve the model aerosol initial conditions and forecasting accuracy of PM2.5, PM10 and AOD. The positive impact on PM2.5 and PM10 forecasting by the assimilation can be maintained for more than 14 h for the case1 and 24 h for the case2, and the initial field of AOD in assimilation experiment has been greatly improved comparing the model control run (cn, without data assimilation). For the simulation of the case2, the assimilation of CALIPSO extinction coefficient profiles reduced the root mean square error (RMSE), mean fraction (MFE) and bias (BIAS) of the AOD in the initial field of the model by 0.08 (19.5%), 0.34 (55.7%) and 0.16 (48.5%) compared to the cn experiment, respectively. When the CALIPSO extinction coefficient profiles and surface PM mass concentration data were assimilated simultaneously, the reduction of the RMSE, MFE and BIAS of the AOD was 0.6 (14.6%), 0.32 (52.5%) and 0.12 (36.4%), respectively. Additionally, aerosol extinction coefficient are remarkably underestimated in the cn experiment, particularly during heavy aerosol pollution case. Assimilating surface PM data can improve the extinction coefficient distribution below 500 m. The simulated aerosol extinction coefficient distribution at 1 km to 2 km can be significantly improved in both cases by assimilating the CALIPSO extinction coefficient profiles, and the value of model simulated extinction coefficient is nearly doubled compared to the cn experiment. Finally, the evaluation with independent ground-based lidar measurements indicates that combined assimilation of surface PM mass concentration and CALIPSO extinction coefficient profile can effectively improve the aerosol distribution near the ground and in the upper layer, and thus generate a more accurate 3D aerosol analysis and forecast field.

Seasonal characteristics of aerosol vertical structure and autumn enhancement of non-spherical particle over the semi-arid region of northwest China

Assessments of the effects of aerosols on the climate and environment still feature large uncertainties, and a better understanding of the spatiotemporal variation in these effects is needed. In this study, coincident observations of ground-based lidar and sun photometer measurements from March 2010 to February 2011 were selected to examine the sensible seasonal characteristics of the aerosol vertical structure and the potential variations of aerosol properties before and during the wintertime heating period at SACOL (Semi-Arid Climate and Environment Observatory of Lanzhou University, 35.946°N, 104.137°E, 1961 m ASL), northwest of China. Our results suggest that the aerosol behavior during a year can be roughly divided into two major periods: the non-spherical particle dominated period and the spherical particle dominated period based on the depolarization ratio, or the dust-dominated period (spring and winter) and the non-dust-dominated period (summer and autumn) based on the aerosol angstrom exponent. The height and width of peak of aerosol scale height frequency distribution show the distribution of aerosol layers in summer is highest, then followed by spring, autumn and winter. The depolarization ratios at different heights in spring are higher than those in other seasons. A similar distribution of extinction coefficients above 2 km can be seen in four seasons, but relatively large differences exist below 2 km, especially within 1 km. The increase of the extinction coefficient is observed near surface in November 2010 with a sharp increase in depolarization ratio which is induced by the rising contribution of the dust events (up to 13%) and the mixed type aerosols (70%). These results not only provide detailed characteristics of aerosol variation over the SACOL region, but also remind us to take into account the potential contribution of dust aerosol to the severe regional air pollution during the wintertime heating period.

Analysis of aerosol optical properties in a Lanzhou suburb of China

In order to accurately identify feature layer and monitor the spatial and temporal distribution of pollutants, the inversion method of lidar measurement based on multiscale algorithm is proposed in this paper. The detection of clouds, aerosols and dust layers using a modified retrieval algorithm for a dual-wavelength lidar is presented at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). Moreover, the aerosol optical depth calculated from the Klett-Fernald algorithm obviously excludes the influence of clouds. Two cases were presented to demonstrate that the modified algorithm can capture low-clouds and dust layers well. The aerosol optical properties including aerosol optical depth (AOD), effective radius, depolarization ratio and black carbon aerosol mass concentration are analysed in terms of their monthly and seasonal variations. It is shown that the maximum of AOD, depolarization ratio and effective radius were found in spring (0.42 ± 0.35, 0.17 ± 0.1, 0.63 ± 0.24 μm) and the minimums were found in summer and autumn. The black carbon aerosol mass concentration varies significantly throughout year, with the maximum value in winter (2.35 ± 1.56 μg m−3) and a secondary maximum in autumn (1.93 ± 1.28 μg m−3), a minimum (1.03 ± 0.76 μg m−3) in spring. The vertical distribution of extinction coefficient has a peak near 1 km (0.1 km−1). The depolarization ratio vertically distributes at approximately 0.15. In general, pollution is more serious in spring and winter at SACOL, the former pollutants are coarse-mode non-spherical dust particles which originate from the Taklimakan Desert and the Gobi Desert, and the latter are fine mode spherical black carbon aerosols and coarse-mode non-spherical dust aerosols which are the results of both local combustion and long-distance transport. The dust particles existed high-altitude transport in spring and winter at SACOL.

Inversion algorithm of vertical visibility based on lidar and its error evaluation

To solve the problem that the non-uniform distribution of extinction coefficients in the vertical direction of the atmosphere makes it difficult to directly measure the vertical visibility by traditional methods, this paper presents a method for calculating the vertical visibility based on lidar detection. Firstly, according to the basic principle of atmospheric radiation transmission and radiation transfer equation, it deduces the calculation formula of vertical visibility, which solves the problem that there is no specific formula for calculating vertical visibility. Secondly, it inverts the extinction coefficient distribution in the vertical direction of the atmosphere by using the lidar equation and Klett algorithm. On this basis, it proposes an iterative algorithm for vertical visibility. Finally, it uses the gray model GM(1,1) and batch statistics algorithm to evaluate the backscattering coefficient obtained by laser radar inversion, and gives the error confidence interval (0.760±0.339)×10−4(srad·km)−1. The results show that the method is a particularly effective one for calculating vertical visibility, which meets the basic requirements of detection, with small error and high precision.

激光雷达探测对流层气溶胶消光系数的统计分布

激光雷达探测对流层气溶胶消光系数的统计分布

Retrieval of Aerosol Components Using Multi-Wavelength Mie-Raman Lidar and Comparison with Ground Aerosol Sampling

We verified an algorithm using multi-wavelength Mie-Raman lidar (MMRL) observations to retrieve four aerosol components (black carbon (BC), sea salt (SS), air pollution (AP), and mineral dust (DS)) with in-situ aerosol measurements, and determined the seasonal variation of aerosol components in Fukuoka, in the western region of Japan. PM2.5, PM10, and mass concentrations of BC and SS components are derived from in-situ measurements. MMRL provides the aerosol extinction coefficient (α), particle linear depolarization ratio (δ), backscatter coefficient (β), and lidar ratio (S) at 355 and 532 nm, and the attenuated backscatter coefficient (βatt) at 1064 nm. We retrieved vertical distributions of extinction coefficients at 532 nm for four aerosol components (BC, SS, AP, and DS) using 1α532 + 1β532 + 1βatt,1064 + 1δ532 data of MMRL. The retrieved extinction coefficients of the four aerosol components at 532 nm were converted to mass concentrations using the theoretical computed conversion factor assuming the prescribed size distribution, particle shape, and refractive index for each aerosol component. MMRL and in-situ measurements confirmed that seasonal variation of aerosol optical properties was affected by internal/external mixing of various aerosol components, in addition to hygroscopic growth of water-soluble aerosols. MMRL overestimates BC mass concentration compared to in-situ observation using the pure BC model. This overestimation was reduced drastically by introducing the internal mixture model of BC and water-soluble substances (Core-Gray Shell (CGS) model). This result suggests that considering the internal mixture of BC and water-soluble substances is essential for evaluating BC mass concentration in this area. Systematic overestimation of BC mass concentration was found during summer, even when we applied the CGS model. The observational facts based on in-situ and MMRL measurements suggested that misclassification of AP as CGS particles was due to underestimation of relative humidity (RH) by the numerical model in lidar analysis, as well as mismatching of the optical models of AP and CGS assumed in the retrieval with aerosol properties in the actual atmosphere. The time variation of lidar-derived SS was generally consistent with in-situ measurement; however, we found some overestimation of SS during dust events. The cause of this SS overestimation is mainly due to misclassifying internally mixing DS as SS, implying that to consider internal mixing between DS and water-soluble substances leads to better estimation. The time-variations of PM2.5 and PM10 generally showed good agreement with in-situ measurement although lidar-derived PM2.5 and PM10 overestimated in dust events.

A new method of measuring boundary value of atmospheric extinction coefficient

We construct a nonlinear equation between the return signal and the boundary value of extinction coefficient according to the lidar equation. And according to the nonlinear equation, we put forward a new method to solve the nonlinear equation by using Broyden algorithm. The Broyden algorithm is a concrete application of the quasi-Newton method. It has faster convergence and less iteration times, and does not need to calculate the derivative value. After choosing a suitable initial value, the boundary value can be obtained through the algorithm. A 532 nm single-band Mie scattering imaging lidar system is developed in Hefei, Southern China, for real-time atmospheric aerosol/particle remote sensing. Atmospheric measurement has been performed in Science Island during night time, and the time-range distribution of atmospheric backscattering signal was recorded on April 6, 2017, by employing the imaging lidar system. Then, the boundary values are achieved based on the Broyden algorithm and the least square algorithm. It adopts the Klett backward integration method to retrieve the horizontal distribution of extinction coefficients in a range of 1 km after the acquisition of the signal by changing the distance, then the horizontal atmospheric transmittance can be achieved based on the path integral. We also conduct a contrast experiment with the one-way transmission of the horizontal light near the ground within the range of 1 km at the same time. The initial site is situated in the experimental room besides the Dongpu reservoir and the end site is located on the second floor of our office building. The important things in this experiment are that the light reaching the target surface must be fully received and the laser power should be monitored at the double-end. Then we can obtain the transmittance by the direct method. By comparing the transmittance from the direct method with the transmittance from imaging lidar between the two different ways, i.e., Broyden algorithm and least square algorithm, then the correlation coefficients are obtained to be both over 0.95 in the period. And the method introduced in this paper is a little better than the least square algorithm with a value of 0.968. Besides, the average relative errors between the two inverse methods and the direct method are 4.66% and 9.10%, respectively. The average relative errors obtained by using the least square algorithm is about twice that by using the Broyden algorithm. It can be concluded that the algorithm introduced in this paper is effective and has certain advantages for the inverse problem.

Physical and optical properties of aerosols in a free tropospheric environment: Results from long-term observations over western trans-Himalayas

Simultaneous and collocated estimates of near-surface mass concentration of black carbon (BC), number size distribution (NSD) and total number concentration (NT) of composite aerosols, columnar spectral aerosol optical depth (AOD) and local meteorological parameters were made from Aug 2009 to July 2012 at the high altitude (4520 m amsl), remote location Hanle in western trans-Himalayas. Even though all the aerosol parameters remain quite low, large annual variations are seen in the monthly mean values of BC (25 ng m−3–181 ng m−3), total number concentrations of composite aerosols (628 cm−3–1500 cm−3) and AOD (0.05–0.16). Size segregated correlation analysis reveals that the BC mass contributes significantly to the size range of 200–400 nm of the submicron aerosol size spectra. The diurnal variation of BC mostly has been dampened; yet seems to be prominent during spring, showing the presence of weak boundary layer dynamics. In contrast, the diurnal fluctuations in total number concentration have been mostly controlled by the new particle formation events, leading to bursts of large concentrations of ultrafine particles, which subsequently undergo coagulation. Spectral dependence of AOD also shows large monthly variations, with the Angstrom exponent varying from ∼0.52 to 1.3, with a mean value of ∼0.95 ± 0.21. The vertical distribution of extinction coefficients, obtained from CALIPSO data, indicates the presence of elevated aerosol layers, attributed mainly to the influence of long range transport of aerosols from the west Asian and Indian desert region.

X-ray tomography of microdefects using a detector with nonuniform surface sensitivity

Transmission tomography is considered for the case of the variable surface sensitivity of a detector. An equation is proposed for a 2D problem that is a correlation between measured intensity and the distribution of extinction coefficient. A method is developed that reduces reconstruction to searching for a system of linear algebraic equations. Simulation experiments demonstrate its advantages over beam tomography approximation.

Updated African biomass burning emission inventories in the framework of the AMMA-IDAF program, with an evaluation of combustion aerosols

Abstract. African biomass burning emission inventories for gaseous and particulate species have been constructed at a resolution of 1 km by 1km with daily coverage for the 2000–2007 period. These inventories are higher than the GFED2 inventories, which are currently widely in use. Evaluation specifically focusing on combustion aerosol has been carried out with the ORISAM-TM4 global chemistry transport model which includes a detailed aerosol module. This paper compares modeled results with measurements of surface BC concentrations and scattering coefficients from the AMMA Enhanced Observations period, aerosol optical depths and single scattering albedo from AERONET sunphotometers, LIDAR vertical distributions of extinction coefficients as well as satellite data. Aerosol seasonal and interannual evolutions over the 2004–2007 period observed at regional scale and more specifically at the Djougou (Benin) and Banizoumbou (Niger) AMMA/IDAF sites are well reproduced by our global model, indicating that our biomass burning emission inventory appears reasonable.

Aerosol retrieval from two‐wavelength backscatter and one‐wavelength polarization lidar measurement taken during the MR01K02 cruise of the R/V Mirai and evaluation of a global aerosol transport model

Using two‐wavelength lidar with one‐wavelength depolarization measurement installed on the research vessel Mirai, we retrieved vertical distributions of extinction coefficients of water‐soluble, sea‐salt, and dust particles at 532 nm. In the retrieval, the mode radii, standard deviations, and refractive indexes for each aerosol component are prescribed; the retrieval uncertainties due to spherical assumption in our dust model are estimated to be 30–50%. The ship‐based measurements were conducted in the western Pacific Ocean near Japan from 14 to 27 May 2001. For the analysis, we applied two‐wavelength lidar algorithms to the three‐channel lidar data, i.e., for signal strengths at 532 and 1064 nm and the total depolarization ratio at 532 nm. Water‐soluble and sea‐salt particles occurred below 1 km, whereas air masses dominated by water‐soluble and dust particles were sometimes found above 1 km. We also investigated the correlation of sea‐salt extinction coefficient with surface wind velocity for various altitudes. A positive correlation was found at low altitude, but no correlation was indicated at high altitude. We also compared the extinction coefficients of water‐soluble and sea‐salt particles directly under cloud bottom with those in clear‐sky. Below clouds, the extinction coefficients of water‐soluble and sea‐salt particles were 1.6 and 1.4 times larger, respectively, than those in clear sky; this could be explained by hygroscopic growth using Hänel theory. Finally, we evaluated the global aerosol transport model SPRINTARS using the retrieved aerosol properties and measured lidar signals. The model underestimated sea salt and overestimated dust, although the general patterns agreed with the observed patterns.

Simultaneous estimation of extinction coefficient distribution, scattering albedo and phase function of a two-dimensional medium

In this work, we develop a scheme based on solving the general integro-differential equation of radiation transport to estimate simultaneously the distribution of the extinction coefficient, the scattering albedo and the phase function of a two-dimensional inhomogeneneous medium with less diffusive radiation. The forward problem for a cylindrical medium subjected to collimated incident radiation is solved by the discrete-ordinate method. The inverse radiation problem is formulated as a least square problem that minimizes the discrepancy between the measured and the calculated leaving radiative fluxes. The Levenberg–Marquardt algorithm is applied to the least square problems for a variety of cases. The results obtained show that this scheme can reconstruct accurate enough results for most of the cases considered. Comparisons of the results show that the accuracy of the estimated results decreases with the increase of the scattering albedo and we need more discrete ordinates to generate accurate enough estimated results for an optically thin case. The estimated results obtained from the measurement data with moderate errors are still acceptable.

X-Ray Tomography in Scattering Media

In this paper we treat the problem of tomography of a medium with a high scattering level. A mathematical approach has been developed for an investigation of the radiation field. Based on these results a special source-detectors configuration is proposed. This offers a separation of the intensity of nonscattered and single-scattered radiation from the intensity of the total flux. The conventional Radon transform procedure can be applied to the data processed that way to reconstruct the extinction coefficient distribution. Then the value of the scattering coefficient at any given point can be found separately by solving a system of simple equations. Finally, we present some numerical results to demonstrate a numerical implementation of the method and the distortion of the body image caused by scattering interference.

Measurement of extinction coefficients of laser-produced aluminum plumes

Radial spectral intensities (0.632 yum) were measured using a He:Ne probe laser scanning an aluminum plume formed by Ndiglass laser irradiation of a target surface. Furthermore, techniques were developed to measure the radial distributions of the extinction coefficients in an axisymmetric, laser-produced aluminum plume. The techniques developed allow for measurements of these distributions as functions of time, wavelength, and elevation above the aluminum target. The extinction coefficients determine the ability of the plasma to attenuate incident laser radiation. The extinction coefficient distribution was determined by scanning a He:Ne probe laser through the plume and converting line-of-sight measurements to a radial distribution. Results indicate that the aluminum plume is optically thin in the first 80 /*s after formation and that the radial extinction coefficient profile has a Gaussian distribution.

Extraction of spatial aerosol distributions from multispectral light extinction measurements with computed tomography

We combine optical remote sensing with computed tomography to determine simultaneously (a) the concentration and (b) the size distribution of particles at every pixel in a plane that slices through an aerosol. Light-extinction measurements are made along intersecting paths that pass through the plane. The spatial distribution of extinction coefficients at multiple wavelengths is obtained by an algebraic image-reconstruction technique (ART3). The size distribution of the aerosol at every pixel in the plane is obtained by inversion of the Fredholm integral equation. Computer simulations of this procedure were conducted. Extinction coefficients were found at all pixels in the plane at multiple wavelengths. Aerosol size distributions were retrieved at four pixels. Results of this analysis show that four projection angles were sufficient for reconstruction of extinction coefficient distributions in the plane. The technique can tolerate up to 10% random, normally distributed noise in the measurements. The size distributions at the four pixels were close to the true distributions. The size of the smallest feature that needs to be recovered should be larger than the ray spacing. We were able to delete three of every four rays and still get good reconstructions.

The relationship of the extinction coefficient distribution to wind field patterns in southern California

Abstract The averaged distribution of the extinction coefficient, including its diurnal variation, in southern California is shown for commonly occurring winter and summer wind field patterns. The wind field patterns were generated by an objectively based method using empirical orthogonal function (EOF) analysis of the vector wind, similarity criteria and cluster analysis. For the days assigned to each pattern, averaged extinction coefficient fields were calculated for six diurnal periods. Three main winter and three main summer patterns were identified. Associated with the wind field patterns were distinctly differing extinction coefficient patterns. Transport of visibility reducing aerosols can be inferred by comparing the wind and extinction fields and their diurnal variation. Transport of visibility reducing pollutants from the Los Angeles Basin and San Joaquin Valley into the Mojave Desert and the south-western U.S. was shown to be highly persistent in summer, while only sporadic in winter. The San Joaquin Valley was identified as having a significant potential for additional visibility impacts in the southwest with higher emissions of visibility affecting pollutants associated with the increasing urbanization of the valley. The analysis illustrated a technique for organizing large wind data sets into a reasonable number of patterns. The clear and consistent relationship between the extinction and wind fields demonstrates the usefulness of this technique in air pollution analysis.