This paper describes an application of the Monte Carlo method to the evaluation of backscattering response to microwave sounding of vegetation. After a brief introductory discussion on the different approaches commonly employed to the numerical simulation of scattering from vegetation, we describe our model based on representing the vegetation medium as a collection of elementary scatterers of simple shapes, and dealing directly with electromagnetic field interaction with these elements. Plant structures are built assembling the single elements by the Lindenmayer systems fractal technique. We presents some examples of computations on models of different kinds of vegetation showing the potential of modeling in understanding scattering behavior. A brief discussion on the issue of second order scattering effects is also included.

In this paper the asymptotic law for the radial distribution of the radiance density from a point isotropic source placed in a slab of a homogeneous absorbing and scattering medium has been obtained. The final formulae have been derived for both the stationary and time-dependent problems. The obtained law has been verified by comparison wiht Monte Carlo simulations.

We study the diffusion of the lidar laser beam in a cloud as it is seen from the receiver. We consider two different types of clouds: an aerosol cloud consisting of randomly oriented oblate spheriods and an ice cloud consisting of randomly oriented oblate cylinders. We calcluate the off-axis diffusion which could be a measured by multiple field of view lidar with circular field stops and the diffusion of the beam in the plane perpendicular to its direction which could be measured by a CCD type device. The simulations were done with or our variance reduction multiple scattering including polarization which is equivalent to a corresponding vector radiative transfer equation and a time continuous Markovian jump process for the description of the transport of light through the atmosphere. The results of these simulations of the off-axis and the planar diffusion are striking: they allow for a simple classification of scattering particles.

Propagation of laser radiation in the atmosphere is susceptible to various degrading effects, one of them is attenuation due to cloud. Recenlty systematic propagation experiments of 4.6μm laser radiation were conducted under a broad range of micro-physical properties of laboratory clouds. An extensive data-base has been obtained, thus provided an opportunity to investigate extinction udner various cloud conditions and the relationship exists between cloud optical and its micro-physical properties. In addition, comparison between the extinction coefficients obtained from experimental measurement and Mie theoretical prediction was conducted. It was proven that both of them agreed favorably well with each other.

We consider here the electromagnetic wave scattering by a long and thin-wire helical particle. In contrast to several previous theoretical works, we adopt here the Mie theory to this case. In the present work a long helical particle is considered as a hollow cylinder with a thin non-homogeneous membrane for which the periodical boundary conditions are imposed.

Solar light scattering from atmospheric layers is perceived by an observer as the background key. The shape of this background is built in the observer's eyes by the visibility distances in all slant directions. In an average day the atmosphere has a turbidity value in the vicinity of 2 implying that the average contribution to the scattered light by the air molecules is approximately equal to the scattering by the spherical and non-spherical particles in the atmosphere. Since the atmospheric air density and the particulate number density in the horizontal direction are both assumed to be constant whereas their values decreases in a slant direction, the resulting varying visibility distances in the various directions are shown to form a flat sky shape. The multiple scattering calculations are based on scattering functions for spherical and non-spherical particles. The basic approach which is used to handle the scattering of non-spherical particles, is discussed in part II of this presentation.

This paper studies the correlation between the time-of-flight (TOF) of laser pulses and the talc content of pulp. Samples of thermomechanical pulp (TMP) and talc were made up with consistency values ranging from 0.0% to 3.0% and increasing by steps of 0.5%. The proportion of filler, in this case talc, in the TMP varied from 0% to 100%. Laser pulses were shot through the samples and changes in the attentation and TOF of the pulses were recorded. The results show that TOF increases as consistenscy increases. This indicates an increase in the number of scattering surfaces. An increase in the proportion of talc leads to a corresponding change in the TOF. This indicates that talc has a larger scattering surface than does TMP of equivalent mass. Varying consistencies and talc contents produced different points on the delay-attenuation axes. Consquently, the measurement of TOF and attenuation may be used to determine the consistency and proportion of talc.

Simulations of scattering and polarization properties for randomly oriented ice crystal particles of various shapes are presented. Analytical procedure of fast averaging over particle orientations is proposed. A pure geometric optics approach is used for visible wavelengths. Within the approach, scattering peaks at forward and backward directions are separated. As a result, the rest Mueller matrix is presented by certain regular functions.

The current implementation of a generalization of the separation of variables method, developed to describe the scattering of electromagnetic waves on non-spherical dielectric particles, is extended to deal with non-axisymmetrical scatterers in spherical coordinates. Computations for finite hexagonal ice columns are performed and compared with results of other methods. Good agreement is obtained. Additionally, a scheme to systematically derive approximations in the treatment of non-axisymmetric particles is proposed. This scheme allows to reduce the numerical effort.

Scattering and radiative models are decisive elements in remote sensing applications. Their accuracy has an essential influence on the accuracy of the retrieved information on the physical and chemical constitution of the earth and its environment. An important scientific goal of the 'Atmospheric Processors' Dept. at the Remote Sensing Technology Institute is the development of sophisticated models to analyze atmospheric light scattering and radiative transfer processes in different spectral ranges. To support the scientific exchange and the usage of these models not only in the various active and passive remote sensing techniques the so-called 'Virtual Scattering and Radiative Transfer Laboratory' was developed. This laboratory is a pilot version of an on-line executable scietnfiic software repository. It is basd on a generic 'Virtual Lab' software infrastructure.

Since the presentation of the virtual backscatter lidar instrument in Firence, a lot of new modules have been added to the virtual instrument. A multiple hard target arrangement with selectable reflection parameters can be placed in a cloud or fog layer to simulate the collision avoidance problem. Further the complete atmospere with aerosols, molecules and clouds can be selected for airborne or spaceborne Doppler lidar simulations.

Boundaries of applicability of the model proposed earlier for the spaceborne laser sounding equation are ascertained for the polarization characteristics of radiation taking into account the contribution of multiple scattering. The algorithm for simultaneous estimating the polarization characteristics and the lidar ratio is described. In some cases it allows to identify the type and size of scattering crystals in cirrus clouds using the data of spaceborne measurements. The results of reconstruction of the cloud parameters are presented for a three-component medium.

This study is devoted to the development of a semi-analytical algorithm for the determination of the otpical thickness, the liquid water path and the effective size of droplets from spectral measurements of the intensity of solar light reflected from water clouds with large optical thickness. The algorithm is planned to be aplied to the data fromteh Scanning Imaging Absorption Spectrometer for Atmospheric Chartography, launched on March 1st, 2002 on board of the ENVIronmental SATellite. The probability of photon absorption by droplets in the visible and near-IR spectral regions is low. This allows us to simplify and modify well known asymptotic equations of the radiative transfer theory, taking into account the fact that the single scattering albedo is close to one. Modified asymptotic equations are used to develop the inverse algorithm. We also avoid the use of the Mie theory, applying parameterization and geometrical optics results with account for wave corrections. The main advantage of the method proposed lays in the fact that the equations derived not only provide a valuable alternative to the numerical radiative transfer solution. They are also much more simple than equations of a conventional asymptotic theory. This simplicity allows both the simplication of the cloud retrieval algorithm and, even more important, insight into various factors involved in cloud retrieval schemes.

Multiple scattering effects on signals from space lidar are significant and must be accounted for in the retreival of aerosol and cloud extinction. It is shown that a simple parameterization of multiple scattering allows one to account for multiple scattering effects using a slightly modified form of a commonly used single-scatter retrieval solution. All orders of scattering are considered in the development of parameterizaiton appropriate for the CALIPSO lidar. Applications to aerosol and cloud retreivals are discussed.

YS Balin and SV Samoilova proposed a lidar equation for the multiple photon scattering process based on the double scattering approximation by Kaul-Samokhvalov. We compare simulations of such lidar return which are obtained by the Kaul-Samokhvalov-Balin-Samoilova approximation and by our Monte Carlo code PBS2.

An analytical approach for modeling Raman lidar return with multiple scattering is presented. The approach is based on a small-angle quasi-single scatteirng approximation developed earlier for elastic lidar sounding. Spatial-angular structure of Raman lidar return is investigated. For particular case of warm clouds it is shown that multiple-field-of-view lidar technique allows one to retrieve the effective size of scattering particles.

The Vaisala ceilometer LD-40 Tropopauser is a compact eye-safe biaxial lidar measuring continuously under all possible climatic conditions and scanning the atmosphere up to a height of 13000 m. It uses laser diodes with 855 nm wavelength that are pulsed at an average frequency of 4000 Hz. The distance of the systems range bins is 7.5 m. Its main task is reporting cloud base heights and vertical visibility for aviation safety purposes. The focus of this appear however is directed on the investigation of backscatter data from falling precipitation. The LD-40 ceilometer is able to detect falling precipitation and it can distinguish between rain and snow by examining backscatter data profiles. This ability is caused by the biaxial lidar optics in combination with the different scattering phase functions of rain droplets and snow. A simple rain-snow discrimination algorithm is introduced, routine at the same place, illustrates the backscatter profile differences between the two optical systems.

Acommercial laser rangefinder was used to measure precipitation. The high pulse repetition rate of the rangefinder (600 Hz) together with a fast digitizer (LeCroy with Ethernet) allows to see single snow flakes or water dropletts. The characteristics of the signals were determined to distinguish between fog, rain and snowfall.

The lidar experimental data recorded for dense stratocumulus clouds above Tomsk city are presented. The measurements were performed by a lidar with changeable field of view (FOV). New algorithms for resolving a lidar equation taking into account multiple scattering have been introduced to restore extinction coefficient profiles. These algorithms are based on the original description of a lidar signal including its asymptotic properties for large FOVs. In order to solve an inverse problem only one parameters, namely the effective particle size has to be a set a priory. From experimental data inversion results it was established that extinction coefficient values in a cloud layer depth are close to the range of 30-40 km_-1.

This work overviews recent advances that have been made in an analytical theory of elastic and Raman lidar returns with multiple scattering and polarization from clouds and seawaters and outlines newly developed software for computer simulation of airborne oceanic lidar performance.

We introduce a stochastic corpuscular multiple scttering process including change of frequency to deal with Raman scattering. Based on this stochastic process, we may derive an exact multiple scattering lidar equation with polarization and change of frequency. We used the construction method of this stochastic process to design a variance reduction Monte Carlo code. This construction is based on transitional probabilities for collision, for directional scattering, and for change of frequency. Shortly we recall the necessary basics of Raman scattering and show how to obtain the transition probabilities for change of frequency. The directional scattering and change of polarization are determined by the Mueller matrices belonging to the scattering particles or molecules. We show the form of the Mueller matrices for elastic and inelastic molecular scattering. Roughly we outline our Monte Carlo code pbs3 and its variance reduction technqiues. Finally, we apply this code to check the influence of multiple scattering on the retrieval of the temperature profile.

Atmospheric depolarization lidar measurements are used to distinguish the solid from the liquid phase of water in clouds an fogs, to study the size distribution of ice crystals and the multiple-scattered contribution to the total energy received. The experimental set-up and preliminary depolarization ratio measurements together with the discussion on the theoretical approach are presented. Water vapor profiles have been performed too, to understand the water motion into the hydrologic cycle.