Calculations of the spectral cloud reflectance over bare soil and vegetation are performed in the framework of the asymptotic radiative transfer theory. A simple equation for the threshold value (THV) of the albedo of the underlying surface is derived. The cases of underlying surfaces with the albedos smaller than the THV can be treated as if the albedo of the surface is equal to zero in satellite cloud remote sensing problems.. It was found that the THV increases with the cloud optical thickness. Also, the differences in light transmission by clouds over bare soil and vegetation are studied.
The author introduces new parameters for ice-cloud retrieval: the reduced optical depth and the particle absorption length. The retrieval of these parameters from backscattering solar light measurements depends only weakly on the assumption on the habits of particles made in retrieval procedures. This allows one to avoid major difficulties in modern ice-cloud retrieval algorithms related to a priori assumptions on the shape of crystals in ice clouds.
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 is devoted to the derivation of approximate analytical equations for the top-of-atmosphere reflection function of a cloudy atmosphere. These equations are based on the analytical solution of the radiative transfer equation valid for optically thick clouds. In particular, we consider the radiative transfer both in the gaseous absorption bands and also in the regions, where gaseous absorption can be neglected. The results obtained are of importance for a number of cloud optics problems including cloud optical and microphysical properties determination from spaceborne optical instruments.
The paper is devoted to the application of the newly developed aerosol retrieval algorithm to a study of the aerosol optical thickness(AOT) spatial distributions for a number of hazard situations including fires and dust outbreaks. In particular we find that the spectral slope of the optical thickness decreases with the distance from a fire. This is owing to the aerosol aging mechanism. Also we discuss possible reasons for the spectral cloud optical thickness anomalous behaviour in the short-wave region.
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.
Approximate analytical solutions for the degree of polarization of light reflected from water clouds are presented. They are valid in the case of optically thick clouds at visible and infrared channels. Equations obtained are used to develop a new semi-analytical cloud retrieval algorithm.
A Monte Carlo code based on the geometric optics approach which applies to spheroids and polyhedral particles composed of one or more materials has been developed. The phase functions of hexagonal solid columns have been integrated with a log-normal particle size distribution and used as an input to the radiation transfer program based on the discrete ordinates method ('rstar' program of Center for Climate System Research, University of Tokyo) to calculate expected measured radiances from space. It was found that a difference of calculated reflected radiances with a case of spherical particles is large. This result indicates that one can not apply the Mie theory, which is valid for retrievals only in the case of spherical particles, to calculate radiative properties of cirrus clouds.
The variability of the phase function of the submicrometer aerosol at large scattering angels was studied in detail. It was found that the coefficient of variance of the phase function has a minimum around the scattering angle 150 degrees. This fact can be used for solution of different atmospheric optics problems, including atmospheric correction ones.
Using the anomalous diffraction approximation of the light scattering theory, it was found that the circular dichroism (CD) and optical rotatory dispersion (ORD) spectra of light scattering media with large soft particles can be represented as linear combinations of CD and ORD spectra of particles' substances. The analytical formulae derived can be used for stereochemical analysis of dispersed systems.
A new analytical solution for the local optical characteristics (extinction, light pressure, and absorption coefficients, asymmetry parameter of a phase function) of spherical polydispersions with comparatively large particles are derived. The geometrical optics (GO) approximation is used to solve the problem. To improve the accuracy of the GO approximation the edge effects were taken into account. A comparison with the Mie theory data shows a fairly satisfactory accuracy of our analytic formulas.