Our work has been limited to find a theoretical modelling for the optical radiation collected by aerospace detectors for image remote sensing.
The model relies on the assump- tion that 'large-angle-scattering' and 'small-angle-scattering' are quasi-independent phenomena. It is qualitatively shown that large-angle-scattering is mainly originated on the first optical path from the top of the atmosphere to the ground , while the second one principally contributes to the small-angle- scattering. The radiative transfer equation RTE that accounts for this phenomenon path is assessed.
It holds for a turbid atmosphere with a free size-distribution of aerosol whose density is allowed to change with the quota. Due to the use of an unknown reflectance distribution of the ground, which is assumed to be uniformly lighted, the radiation field is allowed to be non-uniform for each layer of the accepted plane-parallel geometry of the atmosphere.
The RTE so far obtained is solved by using the 'successive-order-method'. The solution is expressed by a superposing integral of the observed reflectance field, which is not space-shift-invariant. Finally, an approximate technique is described which allows the 'inversion' of the measured radiance to be achieved, and so the retrieval of the reflectance field.
Entropy production and depolarization of multiply scattered light by a random dense medium. Christian Brosseau. We report on the entropic properties of a stochastic radiation field. The degree of polarisation P of light, in the form of plane waves, is of the nature of an order parameter. The radiation entropy takes an analogous form to the entropy of one-dimensional Ising two-level spin systems in contact with a heat bath. On the basis of this analysis the degree of polarisation has a new thermodynamic significance. It is argued that within this representation, one may define an effective polarisation temperature and we show how it depends on the degree of polarisation.
The results are illustrated by two examples: i the computation of the degree of polarisation of an incoherent mixture of partially polarised light beams and ii the problem of entropy production due to multiple scattering of light by a spatially random medium composed of uncorrelated and noninteracting spherical dielectric particles. Light transmitted through a multiple scattering medium is depolarised by decorrelation of the phases of the electric field components and its polarisation entropy increases. The effect of size of the spherical particles and of the optical depth on entropy production are studied numerically, using the Mie theory, via the Monte Carlo method.
Simulation of the upward flux of thermal radiation scattered by aerosols. Vladimir V. Belov ; Sergei V. Afonin ; Irina Y. Makushkina ; Vladimir E. We present the results of statistical simulation of upward flux of thermal scattered radiation in a wide range of variations of characteristics of aerosol extinction and scattering both in the atmospheric boundary layer and in the stratosphere.
We carry out this simulation in case of spatially homogeneous Lambertian surface using the Monte Carlo method. We consider the effect of aerosol upon scattered radiance, characteristics of the adjacency effect as well as the accuracy of both the single scattering approximation and the conservative scattering model. Multiple scattering in space-borne lidar sounding of multilayered clouds.
Cristina Flesia ; Andrei V. Starkov ; Paolo Schwendimann. Due to the big distance between a spaceborne lidar and the sounding targets a great volume of the atmospheric domain is caught within the lidar receiver field of view and the multiple scattering highly affects the lidar returns. Variance reduction Monte Carlo method and analytical extension of the Mie theory are used for the calculation of spaceborne lidar returns from multilayered cloud systems. A main advantage of Monte Carlo techniques is that they allow the calculation of the solution with the desired accuracy. The analytical scattering extension of the Mie theory leads to analytical expressions of the n-fold scattered electromagnetic field and then to a generalisation of the optical parameters.
The performance capabilities of identification of cloud layers from space has been evaluated. The retrieval of the extinction and optical depth in clear and cloudy atmosphere has been carried out by single scattering inversion methods. Propagation and Imaging through Optical Turbulence. Recent developments in optical propagation and imaging through atmospheric turbulence. Anna Consortini. The subject of coherent optical propagation and imaging through atmospheric turbulence, which was extensively investigated after the invention of the laser, has received renewed attention in recent years, both as a tool for investigating the physics of the atmosphere and in view of a number of applications in adaptive systems, in remote sensing and environmental applications.
In the present paper some recent progress will be reviewed, with particular attention to double pass imaging and to the problem of laser scintillation. In double pass imaging, methods have been developed and tested whose aim is the production of images free from turbulence effects. Progress towards the solution of the problem of scintillation includes approximate theory, modelling by means of numerical simulations, and simultaneous measurements of both laser intensity fluctuations and all relevant parameters.
Propagation through complex optical systems: a phase-screen analysis. Larry C. Andrews ; Walter B.
Miller ; Jennifer C. A general analysis is presented for the scintillation index of a Gaussian beam wave propagating through a turbulent medium confined to a portion of the propagation path between input and output planes, the limiting case of which defines a thin random phase screen.
For a plane wave incident on a phase screen located midway between input and output planes, the phase screen scintillation index agrees with that of a plane wave propagating through extended turbulence when the phase variance and spectrum for refractive index of the screen and extended medium are the same. However, for a finite Gaussian beam at the input plane, our analysis reveals that the distance from input plane to the phase screen must be many times greater than the distance from the screen to output plane to simulate a plane wave propagating through an extended medium.
Coherence enhancement of light after double passage through a turbulent medium. Solomon ; Nicholas J. Experimental observation of coherence enhancement phenomenon are presented and described. We have illuminated an optically rough moving target through turbulence using two coherent point sources and observed the interference of the scattered fields in the region close to the sources the region of coherence enhancement with the help of a special interferometric system. Our study shows that the intensity distribution in the region of coherence enhancement depends on the inner scale of turbulence.
Coherent light backscattering by refractive turbulence in the atmosphere. Yurij I.
The E-mail message field is required. Cylindrical lenses are therefore used wherever it is desired to vary the magnification from one meridian to a perpendicular meridian. Later sections of the User Guide provide further details and sample usages, in the context of specific WaveTrain subsystems or of specific functions used to define meshes. The upward and downward scattered flux density by each atmospheric volume and the upward scattered flux surface density at the ground surface. Now we discuss more precisely what this means in WaveTrain. Share Email Print. Standard Atmosphere modeling irradiance spot size on target.
A sharp peak is shown theoretically to exist in angular distribution of light scattered by a layer of ran- dom medium with weak refractive index fluctuations in the vicinity of backward direction. The peak width may be estimated by the ratio of incident radiation wavelength and the turbulence correlation scale. The effect is found to be formed by coherent addition of contributions from elementary layers, and may be considered as an analogue to 'weak photon localisation' phenomena in random media.
When the width of scattering layer is large enough compared with the correlation scale of refractive index inhomogeneities, the differential scattering cross-section is composed by the 'coherent' component and 'incoherent' one, obtained earlier by V. In the case of visible or IR radiation in contrast to microwaves the 'coherent' constituent determines the scattering for large angles close to deg.
Quantitative estimates show the backscattering by turbulent layers in atmosphere to produce noticeable contributions to signal registered in remote sensing monostatic lidar experiments, and thus the effect under consideration has to be taken into account when interpretation of laser remote sounding data is carried out.
Optical simulation of imaging systems using multiple turbulent phase screens. Mikhail A. Vorontsov ; Jennifer C. Ricklin ; Walter B. Miller ; Nikita G. We discuss a technique based on nonlinear and adaptive optics for simulation of phase distortion effects in imaging systems.
This technique uses a nonlinear two-dimensional optical feedback system to produce a controllable spatially and temporally varying chaotic intensity distribution. The intensity pattern is converted into a spatially varying thin phase screen using a spatial phase modulator. A chaotic phase distortion is then introduced into an imaging system's output image by propagation through the phase screen.
A deformable adaptive mirror with computer control is used for simulation of large-scale phase distortions. Optical turbulence effects on focused laser beams: new results. Jennifer C. Miller ; Larry C. We describe recent results explaining the behavior of optical turbulence effects on the propagation of initially convergent focused laser beams. First we discuss the diffractive characteristics of an initially convergent Gaussian beam based on the geometric properties of the diffractive beam parameters.
Some behaviors previously attributed to optical turbulence effects can instead be explained by the diffractive nature of the beam itself. We give expressions for the location and size of the beam waist, maximum possible distance from the transmitter to the beam waist, and the optical radius of curvature for focusing in turbulence. Laser, we present turbulent beam parameters consistent with our previously defined diffractive beam parameters.
Local coherent structures in the light field scattered by atmospheric turbulence and in the image of light source. Ivan G. The generalisation of phase screen model is applied for studying light scattering on atmospheric paths and extended light source image properties. The random phase at the screen by integration along a broken line between source, point on the screen and observer is obtained.
The optimal position of the screen surface and its connection with altitude dependence on atmospheric turbulence is discussed. The limiting conditions for phase screen model application and some possibilities of its improving are considered. The random light field in the observing plane as a sum of light beams scattered by different parts of screen is represented. The local coherent structures, connected with each beam, are described.
The random partial averaged correlation function for light field local properties studying is applied.