By using the Monte Carlo method, we study the dependence of the lidar temporal echo signals on the thickness of the cloud layers. We propose a new technique to reconstruct the optical depth of atmospheric clouds based on the returns of monostatic ground-based and spaceborne lidars with different values of the receiver field of view and laser pulse length.
In the geometrical optics approximation, the scattering of solar radiation in the visible and near-IR regions of the solar spectrum by particles of crystalline clouds is numerically studied. For this purpose an algorithm for direct statistical simulation has been developed. A feature of the algorithm is the ability to obtain the scattering characteristics of solar radiation by crystalline particles of various shapes, concentrations and spatial orientations in a single calculation. Another feature is that, along with particles having smooth surfaces, the processes of radiation scattering on particles with rough surfaces are simulated taking into account the effects of shading and re-reflection. The algorithm is based on the so-called “facet” model of randomly inhomogeneous surfaces. A series of numerical experiments has been performed.
This paper deals with Monte Carlo simulation of the laser beam scattering in the atmosphere clouds or fogs and the laser beam image scanned by a photodetector matrix of the landing navigation system. We study the contribution of radiation for different scattering orders to the photodetector signal intensity.
KEYWORDS: Clouds, Stochastic processes, Monte Carlo methods, Solar radiation models, Atmospheric modeling, Computer simulations, Scattering, Transmittance, Statistical analysis, Photon transport
In this paper, we analyze the influence of the stratus and cirrus horizontal stochastic structures on fluxes of reflected and transmitted radiation. The radiation fluxes were calculated by Monte Carlo method for cloud layers with inhomogeneous optical thickness retrieved during the two field campaigns (CARRIBA and VERDI).
A stochastic non-Gaussian model of the random field of the attenuation coefficient in stratus cloudiness is presented, as well as a weighted Monte Carlo algorithm for simulating the optical radiation transfer in a random cloudy medium.
This paper deals with an ill-posed problem to determine a size distribution for water drops in a cloud from a given scattering phase function. Numerical experiments show that a numerical method based on non-negative least squares with additional requirements of smoothness can be used to solve the ill-posed problem.
The paper deals with the simulation of such optical phenomena as halos, glories and coronas. To simulate these, we use the Monte Carlo method taking into account the multiple scattering of solar radiation. We have developed visualization software to represent computational results.
The paper presents the results of Monte Carlo simulation of the radiation regime in the system “atmosphere - water layer”. The radiation reflection and refraction at the sea surface is simulated with the help of the Fresnel formulas. The facet model is used to describe the sea surface roughness. The vertical stratification of the actinic flux, radiance and angular distributions of the solar radiation are investigated.
KEYWORDS: Monte Carlo methods, Clouds, Solar radiation, Solar radiation models, Scattering, Reflection, Absorption, Ocean optics, Atmospheric modeling, Autoregressive models
This paper presents the results of Monte Carlo simulation of the radiation regime in clouds and describes the effects caused by solar radiation reflected by the underlying surface. Simulation results show that under certain conditions the actinic flux and irradiance can achieve maximal values at specific heights inside clouds.
Numerical data about the sensitivity of the echo-signal to variations in aerosol scattering coefficient define, as is well known, the possibility of solving the inverse problem of atmosphere laser sensing. In this work we analyze the influence of statistic fluctuations of the vertical distribution of the aerosol scattering coefficient on the time distribution of the LIDAR echo-signal in the case of a cloudless atmosphere. We obtain time distributions of intensity, averaged over random instances of aerosol scattering coefficient fields and the corresponding correlation coefficients.
The interaction of radiation of the Novosibirsk Free Electron Laser (FEL) at a wavelength of 130 μm in the atmospheric transmission window with a model aerosol cloud having the known droplet size distribution function has been studied experimentally. The experimental findings are compared with theoretical calculations obtained from solution of the lidar equation for the conditions of the experiment.
The results of numerical simulation of polarization characteristics of terahertz signals from a ground-based remote sensing system in stratus clouds for various models of liquid-droplet clouds are compared. Models of the scattering medium take into account the vertical stratification of the water vapor concentration in the atmosphere. The model of droplet size distribution includes droplets larger than 20 μm in radius. They are referred to as large droplets, while droplets with radius 1<r<20 μm are referred to as small ones. The model of a cloud layer was developed with allowance for a difference in the vertical stratification of the mean radii of the small and large droplets.
In this paper we study the phase functions for water-droplet clouds and fogs computed by the Mie theory for specific bimodal and “mirror”- transformed droplet size gamma-distributions. In addition, we construct images of coronas, fogbows and glory that can occur for such cloud and fog models.
The paper presents results of numerical statistical simulations of experiments of ground-based sensing of cloud layers by terahertz linearly polarized radiation for certain wavelengths from the atmospheric transparency windows. Summarized results of many years’ field measurements of liquid droplet size distributions in temperate latitudes of the Earth and the distributions obtained by aircraft experiments off Great Britain’s coast are used in the scattering layer models. The models of the scattering medium take into account the vertical stratification of water vapor concentration in the atmosphere and the differences in cloud layer microstructure at the top and the base.
Time distributions of ground-based LIDAR echo-signals reflected by the bottom of a liquid droplets cloud were calculated with the help of local estimates of Monte Carlo methods for wavelengths from visible to submillimeter range. The calculations are performed for three models of clouds. In the first model the cloud layer consists only of small droplets of radius from 1 to 20 microns, in the second one there are small and large droplets of radius from 1 to 85 microns and in the third one we take into account small, large and supersize droplets. A density of a particle size distribution is generalized on results of cloud microstructure observations in temperate latitudes. Wavelength range for which one should take into account large and supersize droplets in cloud models is found.
The light haze of a ground-based impulse LIDAR in an altitude-wise optically inhomogeneous cloud-free atmosphere was computed in dependence of various optical-geometrical parameters of the experiment using the Monte Carlo method. Modeling of the LIDAR echo-signal reflected off the lower boundary of a liquid droplet cloud for a ground-based LIDAR and off the upper boundary of the cloud for an aircraft- and space-based LIDAR was also completed. A feature of these calculations is the choice of the model with altitude-wise statistically inhomogeneous structure of aerosol scattering parameters as the optical model of a cloudless atmosphere. The echo-signals from clouds were computed in the assumption of statistical variation of the altitudes of the lower and upper cloudiness boundaries. In the calculations new effective discrete-stochastic modifications of local estimates were employed.
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