Optical characteristics of irregular atmospheric ice columns

The study of cirrus clouds, which significantly affect the climate, is carried out using lidars. Interpretation of the lidar data is based on the direct solution of the problem of light scattering by particles of crystal clouds. Optical characteristics of perfect ice hexagonal columns, obtained previously, poorly agree with the lidar observation results. The work describes calculations of the optical characteristics of irregular hexagonal ice columns, which are in a good agreement with the experimental results. The calculations for particles with deformation of a dihedral angle of 90° are presented. It is shown that the logarithm of the scattering matrix can be linearly approximated well by the logarithm of the particle size. This can significantly accelerate the calculations of the optical characteristics of clouds. It is ascertained that the optical characteristics are in a good agreement with the lidar observation results throughout the range of sizes calculated even at deformation angles of a few degrees

Interference phenomena at backscattering by ice crystals of cirrus clouds

It is shown that light backscattering by hexagonal ice crystals of cirrus clouds is formed within the physical-optics approximation by both diffraction and interference phenomena. Diffraction determines the angular width of the backscattering peak and interference produces the interference rings inside the peak. By use of a simple model for distortion of the pristine hexagonal shape, we show that the shape distortion leads to both oscillations of the scattering (Mueller) matrix within the backscattering peak and to a strong increase of the depolarization, color, and lidar ratios needed for interpretation of lidar signals

Interference phenomena at backscattering by ice crystals of irregular shape

It is shown that light backscattering by hexagonal ice crystals of cirrus clouds is formed by both diffraction and interference phenomena. Diffraction determines the angular width of the backscattering peak and interference produces the interference rings inside the peak. By use of a simplest model for distortion of the pristine hexagonal shape, we show that the shape distortion leads to both oscillations of the scattering (Mueller) matrix within the backscattering peak and to a strong increase of the depolarization, color, and lidar ratios needed for interpretation of lidar signals. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Coherent and incoherent additions of ight beams at solutions of the light scattering problem by use the beam tracing method within the framework of physical optics

Interference effects between the scattered beams in the problem of light scattering by atmospheric ice crystals have been studied. Since the crystals are much larger than the wavelength, it is shown that the interference effects can be neglected if the crystal sizes are statistically varied more than 5% of the mean size. As a result, any calculations of the optical properties of the crystals performing an averaging over crystal sizes can be effectively replaced by the procedure of the incoherent addition of the scattered beams. This procedure allows us decrease the execution time up to 100 times. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Scattering properties of singular and aggregate atmospheric hexagonal ice particles

This paper presents the results of calculating and analyzing the light scattering matrix of aggregates of atmospheric hexagonal ice particles located in cirrus clouds. Two types of basic particle shapes for aggregates are considered: a hexagonal column and a hexagonal plate. For both forms, two types of particle arrangement in aggregates were chosen: compact and non-compact. As a result, 4 sets of aggregates were built: compact hexagonal columns, non-compact hexagonal columns, compact hexagonal plates, and non-compact hexagonal plates. Each set consists of 9 aggregates differing in the number of particles in them, and the particles in each individual aggregate have the same shape and size, but different spatial orientation. The light scattering matrices for all aggregates were calculated for the case of arbitrary orientation in the geometric optics approximation. Dependences of the first element of the matrix on the number of particles in aggregate, with different types of particle arrangement, and for two types of shapes are give

Comparison of the physical optics code with the GOIE method and the direct solution of Maxwell equations obtained by FDTD

A comparison of the physical optics code and GOIE method to solve the problem of light scattering by hexagonal ice crystals has been presented. It was found that in the case of diffraction on a hole in the perpendicular screen, both methods give the same diffraction scattering cross section for the diffraction angles up to 60 degrees. The polarization elements of the Mueller matrix in this case differ significantly even for the angles of 15-30 degrees. It is also shown that in the case of diffraction on the tilted screen, the difference between these methods may be significant. The comparison of the results with the exact solution obtained by FDTD has confirmed that the difference between these methods is not significant for the case of diffraction on the perpendicular screen, but it is slightly preferable to use the GOIE for the calculations. The good agreement with the exact solution confirms the possibility of using the method of physical optics to solve the problem of light scattering by particles with characteristic size greater than 10 microns

Data bank of light backscattering matrices for atmospheric ice crystals of non-convex shape for wavelengths 0.355, 0.532, 1.064 μm

This paper presents the results of calculation and analyzes the light scattering matrix of random oriented ice particles of non-convex shape (hollow column) with cavity angles from 0 to 50 degrees for lidar wavelengths of 0.355, 0.532, and 1.064 microns and refractive indices of 1.3249, 1.3116, and 1.3004. The calculation was carried out within both physical and geometrical optics approximation methods for particle sizes varied from 10 to 100 microns. As a result, it is shown that differential scattering cross-section for non-convex shape (hollow column) demonstrates a power-law dependence on the particle size. However, the linear depolarization ratio has no simple dependence on particle size and is practically independent of wavelength for small particles (L<50 μm). The linear depolarization ratio increases from 0.2 up to 0.5–0.8 with an increase of the cavity angle of the crystal. The elements of the light scattering matrix depending on scattering and cavity angle are give

Backscattering Mueller matrices of 10-100 μm atmospheric ice particles for interpretation of ground-based and space-born lidar data

The paper presents a solution to the problem of light scattering by hexagonal atmospheric plates and columns, as well as irregularly shaped particles with sizes from 10 to 100 microns. The solution is presented in the form of a databank of light backscattering matrices. The solution was obtained for typical wavelengths used in laser sensing problems: 0.355, 0.532, 1.064 μm; as well as for the wavelengths of the near infrared range: 1.55, 2 and 2.15 μm. At wavelengths of 0.532 and 1.064 μm, in addition to the refractive index of ice, the refractive index of the dust aerosol was used: 1.48+i0.002 and 1.6+i0.002, respectively. The solution was obtained within the framework of the physical optics method developed by the authors. Based on the calculated light backscattering matrices, the values of the color and linear depolarization ratios were obtained. It is shown that the power laws previously identified by the authors are violated in the presence of absorption, in particular, for hexagonal particles with sizes up to 100 μm, with an imaginary part of the refractive index greater than i0.0004, significant deviations from the power law are observed. For irregularly shaped particles at wavelengths for which there is no absorption, smooth power law dependences are seen

Software for processing of experimental data on polarization laser sensing of high-level clouds

Methodology for determination of the optical and geometric characteristics of clouds is described. Problems of processing data obtained in experiments on polarization laser sensing of the atmosphere are discussed. Technique for reduction of the phase matrices of cirrus obtained with the high-altitude polarization lidar developed at National Research Tomsk State University to the symmetry plane affixed to the preferred orientation of ice crystals in cirrus is described. The experimental data are compared with the data of numerical modeling of phase matrices in the physical optics approximation and meteorological conditions over the lidar at cirrus altitudes. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Radar-lidar ratio for ice crystals of cirrus clouds

Simultaneous measurement of lidar and radar signals returned from the same cirrus clouds is a prospective method for retrieving the cloud microphysics, i.e. size and shape of the ice crystals constituting the clouds. In this study, the ratio of the backscattered signals of lidar and radar called the radar-lidar ratio has been calculated for the ʱrst time for typical shapes of ice crystals and wide distribution of the crystals over their sizes. It is shown that it is the lidar-radar ratio that is most sensitive to crystal sizes while the lidar depolarization ratio is most sensitive to crystal shape