Backward-scattering Directions Research Articles

Polarization characterization of a nonspherical sea salt aerosol model

The T-matrix method was utilized to study the polarization characteristics of nonspherical sea salt aerosol models within the wavelength range of 0.48–2.5 µm. Analysis was conducted on the polarization characteristics of nonspherical sea salt aerosols across different wavelengths as a function of scattering angle. This included scrutinizing linear depolarization ratios under typical visible and near-infrared wavelengths for various aspect ratios. The impact of particle nonsphericity on the linear depolarization ratios of monodisperse and polydisperse sea salt aerosol particles was examined. The results indicate: (1) In the analysis of the polarization characteristics of sea salt aerosols, the trends of polarization properties are similar between monodisperse and polydisperse systems. The scattering phase function P11(θ) is predominantly more significant in the forward-scattering direction. P11(θ) is insensitive to wavelength changes in the backward-scattering direction. P33(θ)/P11(θ) varies across different bands; in the visible light spectrum, there are significant fluctuating changes, while in the infrared spectrum, it trends towards nearly linear changes. The variation trends of −P12(θ)/P11(θ) and P34(θ)/P11(θ) with scattering angle are similar, and both are significantly affected by changes in wavelength. (2) Regarding the depolarization ratio of sea salt aerosols, the value for polydisperse systems is more than twice that of monodisperse systems, and the greater the nonsphericity, the higher the linear depolarization ratio. In monodisperse systems, at a wavelength of 0.633 µm for visible light and an aspect ratio of 0.4, the maximum depolarization ratio is around 118.82, while at 1.65 µm in the near-infrared, with an aspect ratio of 0.2, the maximum depolarization ratio is near 97.52; under polydisperse conditions, at 0.633 µm for visible light and an aspect ratio of 0.4, the maximum depolarization ratio is around 117.18, while at 1.65 µm in the near-infrared, with an aspect ratio of 0.2, the maximum linear depolarization ratio is near 215.66. Investigating the polarization characteristics and linear depolarization ratios of nonspherical spheroid sea salt aerosol particle models at all scattering angles is important for remote-sensing detection, high-precision calibration, and other optoelectronic applications.

Multiangular spectra of tree bark for common boreal tree species in Europe

Despite the importance of spectral properties of woody tree structures, they are seldom represented in research related to forests, remote sensing, and reflectance modeling. This study presents a novel imaging multiangular measurement set-up that utilizes a mobile handheld hyperspectral camera (Specim IQ, 400–1000 nm), and can measure stem bark spectra in a controlled laboratory setting. We measured multiangular reflectance spectra of silver birch ( Roth), Scots pine ( L.) and Norway spruce ( (L.) Karst.) stem bark, and demonstrated the potential of using bark spectra in identifying tree species using a Support Vector Machine (SVM) based approach. Intraspecific reflectance variability was the lowest in visible (400–700 nm), and the highest in near-infrared (700–1000 nm) wavelength regions. Interspecific variation was the largest in the red, red-edge and near-infrared spectral bands. Spatial variation of reflectance along the tree height and different sides of the stem (north and south) were found. Both birch and pine had increased reflectance in the forward-scattering directions for visible to near-infrared wavelength regions, whilst spruce displayed the same only for the visible wavelength region. In addition, spruce had increased reflectance in the backward-scattering directions. In spite of the intraspecific variations, SVM could identify tree species with 88.8% overall accuracy when using pixel-specific spectra, and with 97.2% overall accuracy when using mean spectra per image. Based on our results it is possible to identify common boreal tree species based on their stem bark spectra using images from mobile hyperspectral cameras.Betula pendulaPinus sylvestrisPicea abies

Light Scattering by Particles with Arbitrary Shape in the Vicinity of the Backward Scattering Direction within Geometrical Optics Approximation

The work presents the solution for the light scattering problem by arbitrarily-shaped particles in the vicinity of the backward scattering direction. The solution was obtained within the framework of the geometrical optics approximation. The refractive index was equal to 1.3116. It was shown that the general contribution of scattering light for arbitrarily-shaped particles in the vicinity of the backscattering direction consists of the specular reflection of the particles and two types of non-specular optical beams. It is shown that the optical characteristics of the ice particles with arbitrary shapes correspond to experimental data.

Interplay of Lorentz-Berry forces in position-momentum spaces for valley-dependent impurity scattering in α−T3 lattices

The Berry-phase mediated valley-selected skew scattering in alpha-T3 lattices is demonstrated. The interplay of Lorentz and Berry forces in position and momentum spaces is revealed and analyzed. Many-body screening of the electron-impurity interaction is taken into account to avoid overestimation of back- and skew-scattering of electrons in the system. Triplet peak from skew interactions at two valleys is found in near-vertical and near-horizontal forward- and backward-scattering directions for small Berry phases and low magnetic fields. Magnetic-field dependence in both non-equilibrium and thermal-equilibrium currents is also presented for valley-dependent longitudinal and transverse transports mediated by a Berry phase. Mathematically, two Boltzmann moment equations are employed for computing scattering-angle distributions of non-equilibrium skew currents by using microscopic inverse energy- and momentum-relaxation times. Meanwhile, a valley-dependent unbalanced thermal-equilibrium anomalous Hall current induced by the Berry force in momentum space, due to different mobilities for two valleys, is also computed for comparisons.

Effects of material parameters upon the dipolar scattering characteristics of uncoated or coated sphere.

An analytical theory for the dipolar scattering characteristics of uncoated or coated sphere with different materials is presented. These materials are magnetodielectric, single negative, single near zero, and double near zero (DNZ) materials. It is shown that an uncoated magnetodielectric sphere has nearly identical E- and H-plane scattered intensities. It is further observed that for an epsilon near zero (ENZ) sphere, the intensity of scattered field in the E plane is nearly isotropic. For a coated sphere, it is shown that a magnetodielectric sphere coated with ENZ and mu near zero materials have nearly identical E-plane scattered intensities in the forward and backward scattering (BS) directions. Likewise, it is also shown that a finite sized magnetodielectric sphere coated with a DNZ layer can be made hidden to the incoming wave in the BS direction.

Applicability of Phase-Function Normalization Techniques for Radiation Transfer Computation

The applicability of recently developed four phase-function (PF) normalization techniques for modeling radiation transfer in strongly anisotropic scattering media is intensively examined using the discrete-ordinates method. The three simple techniques via normalization of only the forward- and/or backward-scattering directions have been shown to reduce normalization complexity while retaining diffuse radiation computation accuracy for Henyey-Greenstein (HG) PFs. For Legendre PFs, however, such simple techniques are found to result in unphysical negative PF values at one or a few correction directions in some cases. Additionally, negative PF values can occur with these simple techniques for ballistic radiation transfer for both HG and Legendre PF types. If negative-intensity correction is applied, however, radiative heat transfer calculation can still converge regardless of the appearance of negative PF values. The relatively complex Hunter and Guo (2012) technique, in which normalization is realized through a correction matrix covering all discrete directions, is shown to be applicable for diffuse and ballistic radiation for both PF types.

Discrimination of wheat crop stage using CHRIS/PROBA multi-angle narrowband data

Multi-angular narrowband compact high-resolution imaging spectrometer (CHRIS) on-board the project for on-board autonomy (PROBA) data of 18 March 2008 were used in this study to discriminate three different growth stages of wheat crop grown in the Central State Farm of Suratgarh, Rajasthan, India. Results showed that the off-nadir view angles performed better than nadir viewing for crop stage discrimination. Among all the off-nadir viewing angles, −55.37° view angle (in the backward-scattering direction) had the highest normalized distance between the crop stage classes. Based on the analysis, the five best bands were identified as 630, 660, 674, 705 and 712 nm for separating wheat at different stages.

Coherence effects in scattering systems of two interacting dipoles at resonance

Coherence effects in the backward-scattering direction, such as enhanced backscattering (EBS) and the appearance of a negative polarization branch (NPB), are investigated for a simple scattering system composed of two dipolelike particles separated by a fixed distance. The influence on these effects of coupling resonances between the particles is analyzed. The appearance of these coherent phenomena (EBS and NPB) and their relationship as a function of the optical properties of the particles (polarizability) and particle separation are also studied.

Polarization charge effects on ion-dust grain collisions in presence of ion drift

The nonuniform polarization charging effects due to the ion flow on the ion-dust elastic collision process is investigated in the presence of ion drift. The Born analysis is considered to obtain the scattering amplitude and cross section as a function of the momentum transfer, Mach number, and Debye length. The result shows that the nonuniform charging effects significantly enhance the differential scattering cross section for backward-scattering directions. It is also found that the nonuniform charging effects are significant for large momentum transfers.

Comparisons of bidirectional reflectance distribution function measurements on prepared particulate surfaces and radiative-transfer models

To understand the connection between single-particle optics and the optics of a closely packed surface, controlled laboratory measurements of bidirectional reflectance distribution functions on layers of polymer and glass spheres are carried out. The measurements are compared with predictions from five radiative-transfer models; the Hapke's models, the Lumme-Bowell model, the BRF algorithm of Mishchenko et al., and the discrete ordinate radiative transfer. It is found that models of strict numerical radiative-transfer equations (RTEs) predict measurements well in some regions but have errors in both forward- and backward-scattering directions. The improved Hapke's model, although it has an anisotropic multiple-scattering term, still produces considerable errors compared with the strict RTE. The difference can be attributed to the exclusion of a diffraction contribution in the Hapke model.

Interference of quantized transition-state pathways in the H + D2 -> D + HD chemical reaction.

The collision-energy dependence of the state-resolved differential cross section at a specific backward-scattering angle for the reaction H + D2 --> D + HD is measured with the D-atom Rydberg "tagging" time-of-flight technique. The reaction was modeled theoretically with converged quantum scattering calculations that provided physical interpretation of the observations. Oscillations in the differential cross sections in the backward-scattering direction are clearly observed and are attributed to the transition-state structures that originate from the interferences of different quantized transition-state pathways.

Triangle amplitude with off-shell Coulomb T matrix for exchange reactions in atomic and nuclear physics.

The lowest-order rescattering contribution (triangle amplitude) in three-body models of exchange reactions with charged particles contains the off-shell two-body T matrix describing the intermediate-state Coulomb scattering of charged subsystems. General properties of the exact exchange triangle amplitude, when the incoming and outgoing particles are on the energy shell, are derived. This includes the analytic behavior, i.e., the positions and characters of its leading singularities, in the cos\ensuremath{\vartheta} plane, where \ensuremath{\vartheta} is the scattering angle, in the vicinity of the forward- and backward-scattering directions. Since for computational reasons the Coulomb T matrix is usually replaced by the Coulomb potential, the effects of such an approximation on the analytic properties are investigated. The theoretically established behavior of the exact and the approximate exchange triangle amplitudes is then illustrated by numerical calculations, for both atomic and nuclear reactions, for energies below and above the corresponding three-body dissociation thresholds, for elastic and inelastic exchange. \textcopyright{} 1996 The American Physical Society.