The effect of global change in the past century, which led to increased levels of pollution and augmented values of cloud coverage, on the time of the apparent Sunrise and Sunset, is suggested to have shortened the day by 1 - 1.5 minutes in the past 4 decades in northern and mid-latitudes. This is supported by photographs of the setting Sun taken in Jerusalem during the months of July and August 2001, which reveal that in over 95% of the cases the Sun completely disappear to the naked eye below marked atmospheric layers at an average elevation angle of 0.5 - 2.5° above the solid earth horizon. Based on trends in past Sunshine Duration measurements, the day shortening effect is expected to increase in the future.

A sky radiometer has been operated in Hong Kong since the beginning of 2002. The seven wavelengths intensities were taken at intervals throughout the day. Inversions were made to retrieve the aerosol column volume concentrations of different aerosol radii. In this paper we presented some monthly averaged results of aerosol optical properties such as single scattering albedo, and optical refractive index. Examples of consecutive measures of the column aerosol properties are given to illustrate the change of air masses -- maritime, continental and urban -- over Hong Kong. Monitoring aerosol properties using sky radiometer has been found to be effective and efficient.

Optical parameters of clouds retrieved from numerous spectral radiation observation of different kinds revealed a dramatic conflict with results simulated with the scattering Mie theory. Namely, true absorption appears greater than it follows from Mie theory and the scattering coefficient together with the optical thickness exhibit clear spectral dependence. Obtained values of the optical parameters easily explain the "anomalous absorption" within clouds heatedly discussed last decade.

Models of remote sensing (RS) and ground-based (GB) data formation are considered together with numerical/computational (NC) modeling for climate and biosphere research. Multispectral RS imagery processing, GB data mapping representation and a testing stage for specified NC experimentation are analyzed in conjunction with modeling procedures of temporal data series analysis for the RS/GB information products and for the NC outputs. Integrated assessment models are the final stage of the relevant (RS, GB, NC) applications. Models of interpretation of multispectral images in visual, infrared and microwave spectral bands are initial to solve the inverse problems of quantitative parameters assessment (the biomass amount, in particular, for forest and other ecosystems). Each pixel of the images under processing are represented in terms of the listed parameters retrieved from space in accordance with the proposed mathematical procedures. These parameters are invariant (not depending on) to angular coordinates of the related targets observation, Sun illumination conditions and the current state of the atmosphere. Basic principles of ecosystems management are derived from the outlined stages of monitoring and modeling.

A one-dimensional planar model is considered of the atmosphere with multi-layer clouds illuminated by a mono-directional parallel flux of solar radiation. A new approach is proposed to radiation transfer modeling and daylight bakground formation for the atmosphere with such clouds that is represented as a heterogeneous multi-layer system each layer of which is described by different optical characteristics. The influence functions of each layer are determined by solutions of the radiation transfer boundary problem with an external mono-directional wide flux while the contribution of multiple scattering and absorption in the layer is taking into account.

Multiple scattering and absorption of inclined narrow beam can be obtained in theory of radiation transfer as a generalized solution in the five-dimensional phase domain of spatial and angular variables concerning boundary layer problem for kinetic equation with a mono-directional pointed source on the boundary of the plane layer. This solution is interpreted in wide classes of mathematical physics problems as an influence function and can be found by the spatial-frequency characteristics method with these characteristics being considered as Fourier-transforms of the influence function on horizontal coordinates.

The optical properties of ice crystals in noctilucent clouds (NLCs) are studied using the Maxwell theory. In particular, the phase matrix of particles is calculated usng the Discrete Dipole Approximation (DDA). The DDA is a very efficient technique for particles having sizes smaller or on the order of the wavelength. This is the case for NLCs particles both in visible and UV.

The paper addresses the problem of extending conventional Monte Carlo procedures to cases of multiple scattering in media with suspensions of non-spherical or chiral particles. Extinction coefficients of the media depend on polarization of radiation. Along the propagation path polarization of radiation changes, unless the field is polarized according to one of two particular modes. The relationship between these modes and the elements of the amplitude scattering matrix for the type of particle is shown by means of a simple formalism, tested with reference to simple shapes and orientation of the particles. Some possibilities for extending Monte Carlo procedures are suggested. A case of small chiral spheres is considered.

Highly peaked phase functions in the integral term of radiative transfer equation (RTE) create difficulties for its numerical solution. After Fourier expansion of this equation the necessity to use high-degree polynomials for the approximation of dependence of harmonics on polar angle arises. High-degree polynomials require in turn high number of grid points for discretisation of the integral term, as with a sparse grid traditionally applied Gaussian numerical scheme does not provide for flux conservation. Processor time consumption increase drastically with the increase of the number of grid points and and for multiple solution of RTE (e.g. for the solution of inverse problem by iterations) traditional approaches can hardly be applied. Development of flux conserving numerical scheme allowing for the arbitrary number of grid points is possible on the basis of finite element method. This method significantly increases the accuracy of calculation of harmonics of intensity in the case of peaked phase function, but the number of harmonics providing for necessary accuracy of total intensity remains high enough. The main reason here is the presence of the peak in the dependence of intensity on azimuth. With certain assumptions it becomes possible to obtain approximate analytical solution for highly peaked phase functions which takes into account multiple scattering and gives rather accurate results in a comparatively wide region near the intensity peak. On the basis of this solution the computational scheme is developed, presenting the final RTE solution as the sum of the above approximate solution and a smooth function, which is obtained by numerically solving the transformed RTE. For this smooth solution of RTE much less harmonics have to be obtained and computer time consumption is significantly reduced.

An approximate analytical method for solving of the vector radiative transfer equation is proposed. The method is based on the assumption that single scattering of light by large-scale inhomogeneities occurs predominantly through small angles. The method is used to calculate the polarization state of multiply scattered light. The results obtained are discussed for various turbid media.

A mathematical model and a Monte Carlo algorithm were developed to simulate radiation transfer in dispersive media that is optically anisotropic with respect to zenith angle of the light beam. The algorithm was created with the purpose to simulate radiation transfer processes in the atmosphere with optically anisotropic clouds (for instance, cirrus clouds). A numerical experiment was performed for a cloud with ice crystals of hexagonal cylinder shape. We compared results for scattering media with particles stochastically oriented in a horizontal plane and in space. It was shown that orientation of particles could strongly affect the albedo of clouds and the shape of halos.

The problems of statistical simulation of light pulse propagation in stochastic scattering media as applied to the problems of laser monitoring of the clouds are considered. A set of Monte Carlo algorithms, allowing the construction of numerical models for the field of multiply scattered narrow light beams in the aerosol atmosphere and continuous cloudiness has been provided for the purpose. A special attention has been paid to solving the problem of optimization of Monte Carlo algorithms. The optimization is based on the method of "dependent trials."

A hypothesis is made that optical anisotropy of clouds in the atmosphere can be implied not only by the shape and the orientation of scattering particles, but furthermore it can be a result of a random non-Poisson distribution of the particles in space. In that way even for water-drop clouds the scattering medium can be appreciably anisotropic if spherical water drops particularly distributed in space. We proposed a heuristic mathematical model of such hypothetical anisotropy on the basis of fractal distribution of particles in space. In addition, we performed a Monte Carlo experiment to study presumable radiation effects caused by "fractal" anisotropy in water-drop clouds.

There are many exact theoretical methods to simulate light scattering by small particles, but only a few of them, including in the first turn the Extended Boundary Condition Method (EBCM), allow one to perform calculations usually required in practical tasks, i.e. to take into account size, orientation and so on distributions of (simple model) scatterers. Importance of these methods caused by their wide applications was stimulating long time investigations of their applicability ranges. We report recent results of the analysis of EBCM-like methods. It is confirmed that the methods give a convergent solution (i.e. are mathematically correct) everywhere under the known conditions of validity of the Rayleigh hypothesis. Convergence of these methods used to calculate only the far-field characteristics of the scattered field (cross-sections, scattering matrix, etc.) occurs under a weaker condition. These general conditions are applied to the particular cases of spheroidal and Chebyshev particles as well as particles with sharp edges, and numerical results confirming the conclusions of our theoretical analysis are presented.

Real scatterers are known to usually have complex shape and some structure. Therefore, to perform light scattering simulations, one should specify their models and select proper computational methods. To help in solution of these problems, we have created an internet cite DOP (Database of Optical Properties of non-spherical particles). The currnet content of the DOP (optical constants, reviews and bibliographies, codes, etc.) is briefly described. A special attention is paid to recently developed fast methods and codes to treat light scattering by non-spherical inhomogeneous particles using the layered models. First results of application of these tools to comparable study of the optical properties of layered particles and particles with inclusions are presented.

The influence of the size, shape and structure of gold and silver nanoparticles on the dielectric environment dependence of their extinction and integral scattering spectra has been studied. Calculations were carried out for spheres and nanoshells (Mie theory), randomly oriented bispheres, spheroids and s-cylinders with hemispherical ends (T-matrix method). The sensitivity of plasmon resonance (PR) turning to variations of the refractive index was studied (n = 1.3 - 1.7) for the particles with different equivolume size. In the case of nanoshells, the metal layer thickness was also varied. For nanoparticles with equivolume diameter 15 nm, the maximal PR shifts is observed in case of bispheres and decreases in the order: nanoshells, s-cylinders (spheroids), spheres. For the particles with diameter 60 nm, the maximal PR shifts is observed in case of nanoshells and decreases in the order: bispheres, s-cylinders (spheroids), spheres. Other things being equal, the PR of silver nanoparticles is more sensitive to the dielectric surroundings as compared to the gold counterparts.

With the use of the expressions obtained by us earlier the extinction efficiency K_ex, absorption efficiency K_a, single scattering albedo A and phase scattering function P(θ)/4π for optical radiation of a crystalline cloud medium were calculated. The optical characteristics mentioned are necessary for calculation of crystalline and mixed-phase clouds radiation properties used in different climate models. The crystalline cloud microstructure model included the ice hexagonal plates and columns cna be arbitrarily oriented in space. Two possible cases of ice crystal orientation in space were considered -- a chaotic orientation and an arbitrary orientation of the prisms main axis and the plates maximum surfaces in the horizontal plane. The hexagonal prism shape factor is c = 2a/l (where 2a is prism diameter and l is its length), 0.05 ≤ c ≤ 10.0. Theoretically estimated values of K_ex for a crystalline medium microstructure were compared with the experimental values K_ex obtained at the IEM. For execution of K_e calculations by hexagonal prisms with a chaotic orientation in space which sizes are comparable with wavelength of incident radiation can be used Mie-Lorentz theory for spherical particles with the same refractive index and effective radius R₃₂. The absorption efficiency K_a by hexagonal prisms with different orientation in space can be calculated using with the suggested expressions for K_a in view effective size R₃₂. For small (diffraction) scattering angles the phase scattering function P(θ)/4π for ice crystals which sizes are more than wavelength with the high precision may be described by the phase scattering function P(θ)/4π for spherical particles with the effective radius R₂ the same as the effective size R₂ for ice crystals.

An optical model for cirrus clouds consisting of ice crystal particles is considered for random particle orientations. In this model, two points and four intervals of the scattering zenith angle are introduced. They are the points of forward and backward scattering and the intervals of 0° - 22°,- 22° - 46°, 46° - 60°, and 60° - 180°. It is argued that light scattering into these intervals are caused by different physical reasons. Therefore, the behavior of the phase functions in these intervals can be modeled independently. It is assumed that these behaviors of the phase functions are scarcely determined by the exact particle shapes but they are mainly determined by certain weight coefficients for wedges that are inherent to the particle shapes. So, the optical model is based on the weight coefficients for the wedges.

Light scattering by hexagonal ice columns and plates is considered within the framework of both the geometric optics and physical optics approaches. The vicinity of the backward scattering direction that is of interest for lidar measurements is discussed in details. It is shown that the angular distribution of the backscatter reveals a fine interference structure.

Scattering matrices are calculated for hexagonal ice columns and plates with preferred orientation near the horizontal plane by means of an algorithm based on geometric optics. Distributions of scattered energy among the various arcs inherent to scattering by oriented crystals are obtained. Impact of small orientation deviations from the horizontal plane is discussed.

The information borne by the characteristics of reflected optical radiation in the cases of single- or double-ended lidar is studied within the framework of a crystal cloud model as a system of oriented crystal plates. It is shown that the variation of the absolute and relative values of the scattering coefficient obtained at small-angle scanning carries the information about the size spectrum of crystal plates and their flutter in atmospheric formations with inhomogeneous composition.

The transport of light through the atmosphere is modeled as a Levy-type Markovian jump process of stochastic corpuscular multiple scattering of photons including polarization. The backward Kolmogorov differential equation of this Markovian jump process is the general radiative transfer equation with polarization. Based on this stochastic multiple scattering process, Monte Carlo codes have been designed to calculate lidar returns containing essential contributions of multiple scattering (dense clouds, space). Since the retrieval of micro-physical cloud parameters is an ill-posed problem, it is necessary to collect as much additional information about the cloud as possible. Such information can be obtained by using multiple field of view lidars or CCD lidars. Based on the stochastic multiple scattering process, a new Monte Carlo code has been designed allowing for the calculation of the off-axis diffusion patterns of the emitted pulsed laser beam as it is "seen from the monostatic or bistatic CCD receiver." These patterns allow for the classification of different types of scattering particles. Some examples of such patterns will be shown for clouds of radiative fog and of collections of randomly oriented oblate and prolate cylinders and spheroids. These patterns allow for a simple classification of clouds.

We measure the cross-polarized backscattered light from a linearly polarized laser beam penetrating a cloud made of spherical particles with a gated intensified CCD camera. In accordance with previously published results, we observe a clear azimuthal pattern in the recorded images. We show that the pattern originates from second order scattering, and that higher-order scattering causes blurring that increases with optical depth. We also find that the contrast of the symmetrical features can be related to the measure of the optical depth. Moreover, by identifying and subtracting the blurring contributions, the resulting pattern provides a "pure" second-order scattering measurement that can be used for the retrieval of droplet size. We apply this technique on a stratus cloud located at 1400 m. The extinction values retrieved on the basis of the laboratory quantification of the blurring of the multiple scattering secondary polarization patterns measured from the ICCD images are then compared with the profile of the extinction coefficient obtained using Bissonnette's algorithm, which is based on the multiple-field-of-view (MFOV) lidar returns.

An analytical solution for calculation of double Raman-Mie scattering in the presence of a cloud is suggested. The model includes the Raman-Mie and Mie-Raman scattering processes occurring in the cloud volume as well as integrated Raman scattering signal from air molecules along the laser pulse from lidar to the cloud base. The developed algorithm allows for the comparison of relative contribution of these processes to the total Raman-shifted lidar signal. For typical lidar and cloud parameters, double scattering is not negligible and its contribution to the Raman signal is around 20%.

This paper discusses the design of a ground based bistatic lidar that will allow the retrieval of the particle size from C1 clouds. Results of all orders of scattering and the Stokes vectors calculated from the PBS Monte Carlo simulation code for specific lidar geometry will be given. From the analysis of the polarization intensities, the extraction of cloud particle size parameters from such bistatic lidar seems feasible.

Reflection, transmission, and absorption of sunlight by clouds plays an important role in climatology. Therefore one goal of lidar remote sensing is the determination of the extinction profile of clouds. We propose a generally applicable retrieval procedure for getting back the extinction profile of a cloud from the lidar return. This method is based on the idea to compare the measured signal with simulated signals which belong to properly parameterized extinction profiles and to search for the minimizing parameter set. The simulation will be done using our variance reduction Monte Carlo program PBS which takes multiple scattering and polarization into account. The search procedure can be deterministic or random search, or a mixture of both. The result of such a retrieval will depend on additional information such as the scattering behavior of the cloud particles which is characterized by their Mueller matrices. Without such additional knowledge the retrieval of the real extinction profile will not be possible, i.e. the inversion is not unique. We shall show some examples. Furthermore, the inversion is ill-posed, i.e., small variations of the lidar return may lead to large variations of the retrieved extinction profile. Our retrieval procedure will allow for a sensitivity analysis of the method and, hence, of this ill-posedness. We shall present such a sensitivity analysis describing the degree of ill-posedness.

Theory of polarized lidar sounding of multiply scattering media with highly anisotropic phase functions which describes angular patterns with representative azimuth structure of the backscattered signal observed through the polarizer and analyzer is proposed. Such patterns were visualized by other investigators in the plane perpendicular to the receiver optical axis in experiments performed on the base of mono-static polarized lidar systems. Previously obtained approximate equations of the vector theory along with generalized approximations earlier developed in the scalar theory form the basis for our theory. Solution expressed through multidimensional integrals which determine return polarization parameters is presented and explained. It accounts for formation of a signal as a process consisting of single scattering events into the backward region and propagation and small-angle scattering into near-forward directions before and after the back-scattering events. The developed solution gives the return angular pattern for any initial and received states of polarization and includes the multiple scattering. Half-analytical fast techniques that have been developed on the base of the obtained solution are used to simulate the near-backscattering patterns. Computed examples of the patterns for the case of scattering in seawaters are shown and discussed.

Laser remote method of oil pollution detection on the rough sea surface is described. The method uses additional information about near-water wind and a special geometrical scheme for surface illumination. It is demonstrated that the offered method allows control of two effects independently and simultaneously: wind wave smoothing and changes of sea surface reflection coefficient. And consequently it allows decision making about oil contamination presence on the sea surface with a high reliability.