Vladimir V. Barun

Methodology and sample results of retrieving aerosol parameters by combined multiwavelength lidar and Sun-sky scanning measurements

Scientific groups engaged within the frame of the observation networks AERONET and EARLINET perform this work. The methodology of coordinated multi-frequency lidar and radiometric investigation of atmospheric aerosols is being developed for using in network observations. The method to process data of a comprehensive experiment utilizes the approach1,2 designed to process CIMEL data. The retrieval of altitude profiles of aerosol parameters is based on solving a common equation set including lidar equations, equations for the whole atmospheric depth, and constraints on the smoothness of the solutions. The results of numerical experiments are given in the paper to estimate errors while retrieving aerosol parameters. The measurement procedure and algorithms for data processing were refined during the summer-autumn, 2002 at the stations of the Institute of Physics (Minsk, Belarus) and Institute of Geophysics (Belsk, Poland). The stations were equipped by devices CIMEL and three-frequency lidars (532, 694, and 1064 nm). The CIMELs operated according to the routine AERONET program during the measurements. To provide gathering the data on the whole areosol layer, a series of lidar observations was made at different elevation angles. A pro9cedure to successively approach to an optimal estimation of aerosol parameters is proposed in this work to enable data processing with real measurement errors. The results of retrieving vertical profiles of aerosol fraction concentrations are presented for different quality of measurement information.

Peculiarities in spectral behavior of optical characteristics of urban aerosols by laser sensing data and model estimations

Within the frame of the program on ecological monitoring of air masses, researchers of the Institute of Physics have performed a series of experiments on multi-frequency atmospheric laser sounding over the industrial region of Soligorsk City, Belarus. We obtained extinction, scattering, backscatter coefficients, and lidar ratio over the wavelength range of 0.38 to 1.06 mkm. There was observed a number of peculiarities in the said spectral dependencies differing from those for quite a pure atmosphere. Specifically, backscatter and lidar ratio spectra could have a maximum within the studied spectral range or increase monotonically towards the infrared edge of the spectral range. As for atmospheric sounding at sites rather distant from high-power polluting sources, one observes usually decreasing corresponding spectral dependencies with wavelength increasing. The same behavior is given by well- known optical models of atmospheric aerosols, e.g. by the WMO model.

A simple model to study heat transfer in two-component biological tissues under laser irradiation

An analytical approach is proposed to treat heat transfer through two-component biological tissues composing of bloodless base and blood vessels under irradiation by a pulse light beam of finite dimensions and arbitrary duration. The approach is based on the optical and thermal tissue model accounting for individual optical characteristics of the above components, heat exchange between them, and convection losses at the interface with any external medium. Under reasonable assumptions, the Green function of the equation set for bloodless tissue and blood is expressed as a product of the corresponding Green function for an infinitely wide beam by a simple radial function determined by the radial shape of the irradiating light. So for any temporal structure of the external radiation, temperature rise of the composite tissue is a single convolution-like integral from analytical functions. This enables us to study explicitly some limiting cases of the heating and cooling. The effects of critical parameters of the problem and asymptotic temperature regimes gain a physically vivid and transparent form. Sample examples of these effects are considered and discussed in the paper.

Simulation of tissue heating by a short light pulse

We have stated and analytically solved heat transfer equations for a multi-component biological tissue iluminated by a temporal delta-pulse at different heat exchange mechanisms between blood vessels and its surroundings of basic tissue and between the tissue as a whole and its ambient external medium. The contribution of each mechanism to temperature fields inside the tissue is studied in detail. Empirical constants of the mechanisms are estimated from rather strict and general viewpoints of thermal physics. Specific numerical values of the constants are given for air or water as the environment. The starting HTEs were substantially simplified by evaluating optical and thermal physical parameters of tissues to show that the tissue can be regarded as optically and thermally uniform with localized light absorption or additional heat sources in blood vessels. The thermal fuction of a human organism is approximated to include the boundary contact of a tissue with an ambient medium having a temperature other than that of the tissue. The applicability limits of the used 1D HTEs are discussed and substantiated for the estimations. Sample results illustrating temporal and spatial temperature distributions for convective and thermal conduction surface losses to the environment are given. It is shown, in particular, that the lower the volume content of blood vessels in tissue, the higher the temperature of the vessels and their tissue surroudings immediately after irradiation. The opposite situation occurs in a fraction of a millisecond after the irradiation, i.e. the tissue temperature increases with the volume content of the vessels.

Non-invasive diagnostics of several structural and biophysical parameters of skin cover by spectral light reflectance

A calculation scheme and an algorithm to simultaneously diagnose several structural and biophysical parameters of skin by reflected light are constructed in the paper. The procedure is based the fact that, after absorption and scattering, light reflected by tissue contains information on its optically active chromophores and structure. The problem on isolating the desired parameters is a spectroscopic one under multiple scattering conditions. The latter considerably complicates the solution of the problem and requires the elaboration of an approach that is specific to the object studied. The procedure presented in the paper is based on spectral tissue model properties proposed earlier and engineering methods for solving the radiative transfer equation. The desired parameters are melanin and blood volume fractions, f and c, epidermis thickness d, mean diameter D of capillaries, and blood oxygenation degree S. Spectral diffuse reflectance R(λ) of skin over the range of 400 to 850 nm was calculated as a first stage. Then the sensitivity of R(λ) to the above parameters was studied to optimize the algorithm by wavelengths and to propose an experimental scheme for diagnostics. It is shown that blood volume fraction and f*d product can be rather surely determined by the reflected green -- red light. One can find f and d separately as well as D by the blue reflectance. The last stage is the derivation of S at about 600 nm.

OPTIMAL REGRESSIONS TO ESTIMATE AEROSOL PARAMETERS BY DATA OF TWO- AND THREE-WAVELENGTH LASER SOUNDING

A problem on introduction of additional a prior assumptions to construct a closed set of lidar equations at several wavelengths and on their solutions to estimate microphysical parameters of atmospheric aerosols by multi-frequency laser sounding data is discussed. Some regression relations between spectral values of aerosol backscatter and extinction coefficients in the visible and near-IR are used as the assumptions. The regressions are constructed by model considerations. The optical atmospheric aerosol model of the World Meterological Organization is taken as a basic one. The constructed regressions enable one to evaluate the solvability of, generally, ill-conditioned lidar equations and the errors in the solutions as well as to make some estimations with respect to the determination of aerosol microstructural parameters. This work has been directed towards the design of procedures and algorithms to process laser sounding data gathered routinely by lidar setups of the Institute of Physics, Belarus National Academy of Sciences, Minsk, Republic of Belarus within the frame of a number of International and National research and development programs.

On asymptotic values of light fluxes scattered by large spherical particles between two angles

The asymptotical limits for light fluxes scattered by large spherical particles with various refractive indices into a fixed range of scattering angles are obtained. Calculations are performed within the framework of the Mie theory and the geometrical optics approximation. The geometrical optics approach, combined with approximations of the radiative transfer theory, allows one to make quick estimates of reflection and transmission functions of disperse media with large particles. The results obtained can be used for studies of light fields in random media with large particles within the framework of the small-angle and quasi-single-scattering approximations of the radiative transfer theory.

Retrieving atmospheric aerosol parameters on the base of multiwavelength lidar and sun sky-scanning radiometer data

A flexible algorithm to commonly process lidar and sun sky-scanning radiometer measurements is developed. The algorithm is oriented towards the engineering facilities of the radiometer CIMEL used by AERONET network and a two-to-four wavelength lidar used by European lidar network EARLINET. Numerical experiments were performed to assess algorithm sensitivity to measurement errors and possible violations of basic model assumptions.

Computational simulation of night vision of retroreflective road markers under poor atmospheric visibility

A method is developed and investigations of the contrast and limiting visibility range of a retroreflective marker defining, for example, the overall-dimensions of a heavy truck are carried out for a case of illumination by anti-fog headlamps, upper or low beam of another vehicle through fog of various optical density with no other external lighting. The studies simulate night vision of non-Lambertian road markers from the viewpoint of the modern image transfer theory. The method enables one to include analytically the effects of multiple light scattering by fog aerosols, different mutual positions of the headlamps, vehicle driver, and object observed, as well as real retroreflective properties of the marker to derive vision characteristics via quite simple formulas. The visual contrast and limiting visibility range values of, respectively, retrorefractive and Lambertian markers are compared to demonstrate the advantages of applying the former for enhancing traffic safety and increasing allowable road speed. The recommendations are made with respect to the use of retroreflective markers as an auxiliary signaling means to show the overall dimensions.