Backscattering Cross Section Research Articles

Dephasing effect on backscattering of helical surface states in 3D topological insulators.

We analyze the dephasing effect on the backscattering behavior of the helical surface states in 3D topological insulators. We show that the combination of dephasing and impurity scattering can cause backscattering in the helical states. Especially for the charge impurity case, the backscattering cross section becomes extremely large around the Dirac point. This large backscattering behavior can lead to the anomalous "gaplike" features found in recent experiments [T. Sato et al., Nat. Phys. 7, 840 (2011)].

Electromagnetic scattering by approximately cloaked cylindrical bodies with nonhomogeneous anisotropic cloaking material

In cloaking, a body is hidden from detection by surrounding it by a coating consisting of an unusual anisotropic nonhomogeneous material. The permittivity and permeability of such a cloak are determined by the coordinate transformation of compressing a hidden body into a point (3D or spherical configuration) or a line (2D or cylindrical configuration). Some components of the electrical parameters of the cloaking material are required to have infinite or zero value at the boundary of the hidden object. Approximate cloaking can be achieved by transforming the cylindrical bodies (dielectric and conducting) virtually into a small cylinder rather than a line, which eliminates the zero or infinite values of the electrical parameters but produces scattering. The solution is obtained by rigorously solving Maxwell equations using angular harmonics expansion. In this work, the scattering pattern and the back-scattering cross-section against the frequency for cloaked conducting and dielectric cylinders are studied for both transverse magnetic (TMz) and transverse electric (TEz) polarizations of the incident plane wave for different transformed body radii.

Detection of preferential particle orientation in the atmosphere: Development of an alternative polarization lidar system

Increasing interest in polarimetric characterization of atmospheric aerosols has led to the development of complete sample-measuring (Mueller) polarimeters that are capable of measuring the entire backscattering phase matrix of a probed volume. These Mueller polarimeters consist of several moving parts, which limit measurement rates and complicate data analysis. In this paper, we present the concept of a less complex polarization lidar setup for detection of preferential orientation of atmospheric particulates. On the basis of theoretical considerations of data inversion stability and propagation of measurement uncertainties, an optimum optical configuration is established for two modes of operation (with either a linear or a circular polarized incident laser beam). The conceptualized setup falls in the category of incomplete sample-measuring polarimeters and uses four detection channels for simultaneous measurement of the backscattered light. The expected performance characteristics are discussed through an example of a typical aerosol with a small fraction of particles oriented in a preferred direction. The theoretical analysis suggests that achievable accuracies in backscatter cross-sections and depolarization ratios are similar to those with conventional two-channel configurations, while in addition preferential orientation can be detected with the proposed four-channel system for a wide range of conditions.

Characterizing falling snow using multifrequency dual-polarization measurements

Combinations of dual-polarization measurements at various radar frequencies and elevation angles together with realistic scattering computations of snowflakes are compared in order to study how they can be used to characterize falling snow. In the study, we use seven different ice crystal habits, including graupel, and different types of aggregates. The single-particle scattering is modeled using the discrete-dipole approximation, and the backscattering cross sections are integrated over exponential size distributions. We take advantage of statistical properties of the large set of scattering results to determine which combination of measurements provide overall best characterization of snow types. We find that a combination of the differential reflectivity and the depolarization ratios, especially in the circular basis, is useful in the characterization, while the dual-frequency ratios at higher frequencies than the Ku band are almost as good. Also, the assumption of preferential orientation for single ice crystals plays an important role when analyzing the results. These conclusions are tested against both airborne and ground-based radar measurements obtained during the Global Precipitation Measurement Cold-season Precipitation Experiment field campaign in 2012. The results show that dual-polarization and dual-frequency measurements provide complimentary information and can narrow down the characterization of falling snow considerably.

New insight into particulate mineral and organic matter in coastal ocean waters through optical inversion

Suspended particulate inorganic matter (PIM) and particulate organic matter (POM) often exhibit significant variation both spatially and temporally in coastal oceans. The size distributions and optical properties of these particles are poorly known. Utilizing a newly developed inversion technique from the measured angular scattering pattern, we were able to examine POM and PIM in terms of detailed particle size distributions (PSD) and optical volume scattering functions (VSF), gaining further insights and knowledge of particles that will greatly improve biogeochemical investigations and remote-sensing algorithms. We report the results on two extremes or end-members of possible coastal environments, sediment-laden, turbid Mobile Bay, Alabama, USA and biologically productive, clear water Monterey Bay, California, USA. The optically inferred mass concentrations of PIM and POM, when accounting for the fractal nature of suspended particles, agreed well with the respective gravimetric determinations within the analysis and inversion uncertainty. Despite intra- and inter-site variability, the inferred PSDs in both coastal regions commonly showed an apparent background population of PIM at radii <0.6–1 μm overlaid by POM of radii between 2 and 20 μm. The PSDs also saw increased contribution by PIM at radii >50 μm. The clearly distinctive PSDs between PIM and POM provide evidence to support the Risović two-component model for suspended particulates. The shape of the VSFs, i.e., the scattering phase functions, for POM are similar between the two sites (backscattering ratio ≈ 0.0015), but the PIM in Monterey Bay exhibited a higher backscattering ratio than in Mobile Bay (backscattering ratios 0.012 vs. 0.008, respectively). At both sites, the mass-specific scattering cross section values for PIM (σ[PIM]) are about 70–80% lower than σ[POM], while the mass-specific backscattering cross section values for PIM (σb[PIM]) are 10–25% greater than σb[POM].

The Role of Resonance Frequency of the Plasmons in Electromagnetic Wave Scattering Process from a Dielectric Covered Metallic Rod Placed in a Plasma Antenna

The electromagnetic wave scattering due to excitation of surface plasmons from a metallic rod with dielectric layer embedded in the long plasma column is investigated. In the first part, for short-wavelength waves by investigating the variations of surface polarized charge density on the boundaries, the resonance frequencies and the effective factors on it such as the geometrical dimensions, the radius of the metal, the dielectric thickness, and the plasma radius will be analyzed. In the second part, for presenting an exact analysis and categorizing types of resonant frequency to the dominant resonant frequency and subsidiary resonant frequency of the plasmons, the scattering of long-wavelength waves from the mentioned object will be reviewed. In both cases, the backscattering cross section which is a scale of the scattered power in the direction of incident will be presented.

Calibrated Full-Waveform Airborne Laser Scanning for 3D Object Segmentation

Segmentation of urban features is considered a major research challenge in the fields of photogrammetry and remote sensing. However, the dense datasets now readily available through airborne laser scanning (ALS) offer increased potential for 3D object segmentation. Such potential is further augmented by the availability of full-waveform (FWF) ALS data. FWF ALS has demonstrated enhanced performance in segmentation and classification through the additional physical observables which can be provided alongside standard geometric information. However, use of FWF information is not recommended without prior radiometric calibration, taking into account all parameters affecting the backscatter energy. This paper reports the implementation of a radiometric calibration workflow for FWF ALS data, and demonstrates how the resultant FWF information can be used to improve segmentation of an urban area. The developed segmentation algorithm presents a novel approach which uses the calibrated backscatter cross-section as a weighting function to estimate the segmentation similarity measure. The normal vector and the local Euclidian distance are used as criteria to segment the point clouds through a region growing approach. The paper demonstrates the potential to enhance 3D object segmentation in urban areas by integrating the FWF physical backscattered energy alongside geometric information. The method is demonstrated through application to an interest area sampled from a relatively dense FWF ALS dataset. The results are assessed through comparison to those delivered from utilising only geometric information. Validation against a manual segmentation demonstrates a successful automatic implementation, achieving a segmentation accuracy of 82%, and out-performs a purely geometric approach.

Approximate electromagnetic cloaking of a conducting cylinder using homogeneous isotropic multi-layered materials

Cloaking refers to hiding a body from detection by surrounding it with a coating consisting of an unusual anisotropic nonhomogeneous material. Its function is to deflect the rays that would have struck the object, guide them around the object, and return them to their original trajectory, thus no waves are scattered from the body. The permittivity and permeability of such a cloak are determined by the coordinate transformation of compressing a hidden body into a point or a line. Some components of the electrical parameters of the cloaking material (ɛ, μ) are required to have infinite or zero value at the boundary of the hidden object. Approximate cloaking can be achieved by transforming the cylindrical body (dielectric and conducting) virtually into a small cylinder rather than a line, which eliminates the zero or infinite values of the electrical parameters. The radially-dependent cylindrical cloaking shell can be approximately discretized into many homogeneous anisotropic layers; each anisotropic layer can be replaced by a pair of equivalent isotropic sub-layers, where the effective medium approximation is used to find the parameters of these two equivalent sub-layers. In this work, the scattering properties of cloaked perfectly conducting cylinder is investigated using a combination of approximate cloaking, together with discretizing the cloaking material using pairs of homogeneous isotropic sub-layers. The solution is obtained by rigorously solving Maxwell equations using angular harmonics expansion. The scattering pattern, and the back scattering cross section against the frequency are studied for both transverse magnetic (TMz) and transverse electric (TEz) polarizations of the incident plane wave for different transformed body radii.

Electron scattering in graphene by impurities with electric and magnetic dipole moments

The elastic electron scattering by impurities with electric and magnetic dipoles in graphene is studied with the help of Born approximation. Both types of scatterers give the nonzero cross section of backscattering. The scattering by the impurities with electric dipoles is more efficient even comparing to the scattering by the nanomagnets with anomalous magnetic moments. A comparison of the electron scattering transport cross sections by charged impurities and impurities with electric dipole moments shows that they can be comparable. The scattering by the impurities electric dipoles can be important in limiting the electron mobility in graphene along with the Coulomb scattering.

Radiometrically Calibrated Features of Full-Waveform Lidar Point Clouds Based on Statistical Moments

Full-waveform lidar has gained increasing attention in 3-D remote sensing and related disciplines during the last decade due to its capability of delivering both geometric and radiometric information in the same spatial resolution. Radiometric information may either be related to the echo, e.g., echo amplitude and width, or to the target itself, e.g., the backscatter cross section (BCS). Echo parameters, often obtained by Gaussian decomposition, as well as target properties, which are (geo)physical properties and therefore independent of data acquisition mission parameters, are considered as additional features of the point cloud generated by laser scanning. The BCS commonly is derived by performing a deconvolution which results in its temporal derivative, the differential backscatter cross-section (dBCS), and subsequent integration. The temporal shape of the dBCS has gained little attention in the literature so far. In this letter, we discuss the derivation of additional target parameters, namely the statistical moments of the respective target dBCS. Besides discussing the applicability of established deconvolution approaches for the extraction of statistical moments in the dBCS, special emphasis is laid on their derivation in B-spline-based deconvolution. Uniform B-splines allow for linear deconvolution and subsequent radiometric calibration. We illustrate the potential of the proposed method by a sample data set stemming from an airborne lidar campaign in complex mountainous terrain.

ELECTROMAGNETIC SCATTERING BY APPROXIMATELY CLOAKED DIELECTRIC CYLINDER

In cloaking, a body is hidden from detection by surrounding it by a coating consisting of an unusual anisotropic nonhomogeneous material. The permittivity and permeability of such a cloak are determined by the coordinate transformation of compressing a hidden 2D or cylindrical body into a line. Some components of the electrical parameters of the cloaking material (;) are required to have inflnite or zero value at the boundary of the hidden object. In order to eliminate the zero or inflnite values of the electrical parameters, approximate cloaking can be used by transforming the cylindrical body virtually into a small cylinder rather than a line, but this produces some scattering. The solution is obtained by rigorously solving Maxwell equations using angular harmonics expansion. In this work, the scattering pattern, and the backscattering cross section against the frequency for cloaked dielectric cylinder are studied for both transverse magnetic (TMz) and transverse electric (TEz) polarizations of the incident plane wave for difierent transformed body radii.

THEORETICAL STUDY ON SINGLE-SCATTERING PROPERTIES OF ICE PARTICLES OF DIFFERENT ORIENTATION AT 94 GHZ

The single-scattering properties of hexagonal columns and plates were studied using Discrete Dipole Approximation at 94GHz, including scattering e-ciency, absorption e-ciency, asymmetry factor, backscattering cross section and phase function. Random and horizontal orientations of particles were compared, and 35 sizes of maximum dimension D ranging from 1m to 10mm were selected. The results indicate that scattering and absorption e-ciencies of horizontally oriented hexagonal columns are larger than those of the randomly oriented ones, whereas this phenomenon does not appear to hexagonal plates. The asymmetry factor of horizontally oriented hexagonal plates has a negative value, which means that the backscattered energy is more than forward energy when the particle is large enough. The backscattering cross sections of horizontally oriented hexagonal columns and plates are larger than those of random orientation, which can be explained by that difierent cross sections of particles will be exposed to incident plane wave. When the particle size is smaller than incident wavelength, little scattering energy difierence between random and horizontal orientation exists, while if the particle is larger than incident wavelength, a turning point will happen at µ = 110 - , which can be explained by the theory of energy conservation.

Long Plasma Column With a Non-Coaxial Dielectric Rod Irradiated by an Electromagnetic Wave

The scattering of a plane electromagnetic wave from dielectric rod surrounded by an eccentrically plasma layer is investigated. The graphs of backscattering cross section, scattering pattern and also their corresponding polarized charge density are presented. Investigation has been done on the effects of system parameters and axis separation on the scattered wave resonances.

Dielectric constant adjustments in computations of the scattering properties of solid ice crystals using the Generalized Multi-particle Mie method

Ice crystal scattering properties at microwave radar wavelengths can be modeled with the Generalized Multi-particle Mie (GMM) method by decomposing an ice crystal into a cluster of tiny spheres composed of solid ice. In this decomposition the mass distribution of the tiny spheres in the cluster is no longer equivalent to that in the original ice crystal because of gaps between the tiny spheres. To compensate for the gaps in the cluster representation of an ice crystal in the GMM computation of crystal scattering properties, the Maxwell Garnett approximation is used to estimate what the dielectric function of the tiny spheres (i.e., the inclusions) in the cluster must be to make the cluster of tiny spheres with associated air gaps (i.e., the background matrix) dielectrically equivalent to the original solid ice crystal. Overall, compared with the T-matrix method for spheroids outside resonance regions this approach agrees to within mostly 0.3dB (and often better) in the horizontal backscattering cross section σhh and the ratio of horizontal and vertical backscattering cross sections σhh/σvv, and 6% for the amplitude scattering matrix elements Re{S22−S11} and Im{S22} in the forward direction. For crystal sizes and wavelengths near resonances, where the scattering parameters are highly sensitive to the crystal shape, the differences are generally within 1.2dB for σhh and σhh/σvv, 20% for Re{S22−S11} and 6% for Im{S22}. The Discrete Dipole Approximation (DDA) results for the same spheroids are generally closer than those of GMM to the T-matrix results. For hexagonal plates the differences between GMM and the DDA at a W-band wavelength (3.19mm) are mostly within 0.6dB for σhh, 1dB for σhh/σvv, 11% for Re{S22−S11} and 12% for Im{S22}. For columns the differences are within 0.3dB for σhh and σhh/σvv, 8% for Re{S22−S11} and 4% for Im{S22}. This method shows higher accuracy than an alternative method that artificially increases the thickness of ice plates to provide the same mass as the original ice crystal.

Fraunhofer Lidar Prototype in the Green Spectral Region for Atmospheric Boundary Layer Observations

A lidar detects atmospheric parameters by transmitting laser pulse to the atmosphere and receiving the backscattering signals from molecules and aerosol particles. Because of the small backscattering cross section, a lidar usually uses the high sensitive photomultiplier and avalanche photodiode as detector and uses photon counting technology for collection of weak backscatter signals. Photon Counting enables the capturing of extremely weak lidar return from long distance, throughout dark background, by a long time accumulation. Because of the strong solar background, the signal-to-noise ratio of lidar during daytime could be greatly restricted, especially for the lidar operating at visible wavelengths where solar background is prominent. Narrow band-pass filters must therefore be installed in order to isolate solar background noise at wavelengths close to that of the lidar receiving channel, whereas the background light in superposition with signal spectrum, limits an effective margin for signal-to-noise ratio (SNR) improvement. This work describes a lidar prototype operating at the Fraunhofer lines, the invisible band of solar spectrum, to achieve photon counting under intense solar background. The photon counting lidar prototype in Fraunhofer lines devised was used to observe the atmospheric boundary layer. The SNR was improved 2-3 times by operating the lidar at the wavelength in solar dark lines. The aerosol extinctions illustrate the vertical structures of aerosol in the atmospheric boundary over Qingdao suburban during summer 2011.

Electromagnetic wave scattering from a magnetized plasma column including a thin annular magnetized relativistic rotating electron beam (TAMRREB)

The problem of the scattering of electromagnetic waves from a magnetized plasma column including a thin annular magnetized relativistic rotating electron beam is discussed theoretically. The backscattering cross-section and scattering pattern are presented for a transverse electric (TE) polarization. An investigation on the effects of system parameters on the backscattering cross-section and scattering pattern is done and the corresponding polarized charge density plots are presented.

Modeling radar backscattering from melting snowflakes using spheroids with nonuniform distribution of water

In a number of studies it is reported that at the early stages, melting of aggregate snowflakes is enhanced at lower parts. In this paper, the manifestation of the resulting nonuniform distribution of water is studied for radar backscattering cross sections at C, Ku, Ka and W bands. The melting particles are described as spheroids with a mixture of water and air at the bottom part of the particle and a mixture of ice and air at the upper part. The radar backscattering is modeled using the discrete-dipole approximation in a horizontally pointing geometry. The results are compared to the T-matrix method, Mie theory, and the Rayleigh approximation using the Maxwell Garnett mixing formula. We find that the differential reflectivity and the linear depolarization ratio show systematic differences between the discrete-dipole approximation and the T-matrix method, but that the differences are relatively small. The horizontal cross sections show only small differences between the methods with the aspect ratio and the presence of resonance peaks having a larger effect on it than the nonuniform distribution of water. Overall, the effect of anisotropic distribution of water, reported for early stages of melting, is not significant for radar observations at the studied frequencies.

On the problem about determination of the sea wave period based on radio altimeter data

We consider the features of backscattering of electromagnetic microwaves during nadir sounding of the sea surface. Combined analysis of radar data and sea buoy information allowed us to refine the connection between the parameters of the waves and the reflected radar signal. It is shown that knowing of the wind velocity and the wave steepness or the slope variance of largescale waves is sufficient to calculate the cross section of the backscattering at a zero incidence angle. Several types of wave periods were used as quantitative characteristics of sea waves. It has been shown that the sea wave characteristics can be retrieved from radio altimeter data. The comparison of the retrieved and measured parameters confirmed the efficiency of the developed algorithms. One can state that the allowance for these data in numerical sea wave models will make it possible to improve the accuracy of numerical modeling of the wave environment. A nonmonotonic dependence of wave periods on the backscattering cross section has been found.

Modeling the microwave single‐scattering properties of aggregate snowflakes

AbstractA new snowflake aggregation model is developed to study single‐scattering properties of aggregate snowflakes. Snowflakes are generated by random aggregation of six‐bullet rosettes constrained by size‐density relationships derived from previous field observations. Due to random generation, aggregates may have the same size or mass, yet different morphology allowing for a study into how shape influences their scattering. Single‐scattering properties of the aggregates were investigated using discrete dipole approximation (DDA) at 10 frequencies. Results were compared to those of Mie theory for solid and soft spheres (density 10% that of solid ice) and to T‐matrix results for solid and soft spheroidal cases with aspect ratios of 0.8. Above size parameter 0.75, neither the solid nor the soft sphere and spheroidal approximations accurately represented the DDA results for aggregates. Asymmetry and the normalized scattering and backscattering cross sections of the aggregates fell between the soft and solid spherical and spheroidal approximations. This implies that evaluating snow scattering properties using realistic shapes, such as the aggregates created in this study, is of paramount importance. Concerning the morphology of the aggregate snowflakes created in this study, the dependence of their single‐scattering properties on each aggregate's detailed structure seemed of secondary importance. Using normalized standard deviation as a measure of relative uncertainty, it is found that the relative uncertainty in backscattering arising from the different morphologies caused by random aggregation is typically ~15% for individual particles and ~18% when integrated over size distributions. Relative uncertainties for other single‐scattering parameters are less.

Modeling microwave backscatter and thermal emission from linear dune fields: Application to Titan

We present an electromagnetic model that relates the microwave backscatter and thermal emission from linear dune fields to their compositional, physical (roughness, subsurface porosity/heterogeneity) and geometrical (slope, orientation) properties. This model shows the value of exploring these highly directional and geometrical features in light of both their backscattering cross-section and emissivity. Compared to Cassini concurrent radar and radiometry data acquired from October 2004 to June 2011 over Titan’s dune fields, it provides clues to understand variations among dune regions on the largest Saturn’s moon. In particular, it brings a formal support to the idea first advanced in Le Gall et al. (Le Gall, A., Janssen, M.A., Wye, L.C., Hayes, A.G., Radebaugh, J., Savage, C., Zebker, H., Lorenz, R.D., Lunine, J.I., Kirk, R.L., Lopes, R.M.C., Wall, S., Callahan, P., Stofan, E.R., Farr, T. and the Cassini Radar Team [2011]. Icarus 213, 608–624) that the size of the interdune valleys (relative to that of the dunes) varies across Titan as well as the diffuse scattering properties of these interdune areas due to different thickness of sand cover (i.e. bedrock contribution) or degree of compaction/heterogeneity of the sand cover. The Fensal and Belet dune fields, in particular, are quite different in terms of these properties. The comparison between the model and Cassini data also reveals the potential presence of structures, possibly small-superposed dunes, oriented perpendicular to the dune crests in the Aztlan region.