The SSA+ for scattering from dielectric surfaces at very low grazing angles

Previously we developed a practical model for scattering from randomly-rough surfaces at very low grazing angles for the Dirichlet problem which was found to give good numerical results. In this paper, we derive the expression for the bistatic scattering cross-section for the non-local small slope approximation for dielectric interfaces. We then extend our practical model to dielectric surfaces based on this result. We discuss numerical results for scattering at low forward grazing angles for a Gaussian roughness spectrum with an angle of incidence of 80^○.     

Anomaly in α-scattering from 6Li between 35 and 45 MeV

The elastic scattering of α-particles on ⁶Li nuclei has been measured from 20° to 170° (c.m.) and the inelastic scattering to the first excited state of ⁶Li has been measured for forward and backward angles. The elastic scattering angular distributions are calculated (i) in terms of pure potential scattering, (ii) in terms of potential scattering with an l-cut-off on the imaginary part of the potential and (iii) in terms of the coherent addition of the potential scattering amplitude and of the exchange amplitude. The third method gives the best fit to the data. The inelastic angular distributions are compatible with the macroscopic calculations, except in the very backward region where exchange phenomena are also shown to dominate.     

Differential cross sections for np and nd elastic scattering near 130 MeV

We have measured the np (nd) elastic scattering cross sections at 25(17) angles in the interval 30°–168° (c.m.), using a neutron beam with a broad spectrum peaked near 130 MeV. At backward angles the outgoing charged particles from a liquid hydrogen (deuterium) target were detected; at forward angles we detected neutrons scattered from a hydrogenated (deuterated) scintillating target. Cross sections have been normalized to the energy dependent solution of the Livermore nucleon-nucleon partial wave analysis, evaluated at 130 MeV. The np measurements represent a marginal improvement on previous work; the nd cross sections show some differences from pd measurements, in agreement with earlier indications at an energy of 152 MeV.     

Proton spin relaxation and self-diffusion in some ‘isotropic’ nematogens

Angular distributions of reactive scattering arising from a long-lived collision complex dissociating via a transition state that approximates to a linear rotator are predicted for H atom displacement occurring over a distribution of bending angles β with respect to the rotator axis. A conical angular distribution may be generated when only a narrow range of bending angles contributes to the reactive scattering. However, the angular distribution may take on quite different character as the distribution of bending angles becomes broader. Thus, an isotropic angular distribution is generated by a bending angle distribution which follows the spherical polar weighting P(β) ∝ sin β. Forward and backward scattering is generated by bending angle distributions favouring less strongly bent displacement, while sideways scattering is generated by a bending angle distribution favouring more strongly bent displacement. The experimental angular distribution for OH + CO reactive scattering which shows mild forward and backward peaking, corresponds to a range of bending angles for H atom displacement from the H-OCO transition state which is broadened about the nominal preferred direction β = 45° but avoids strongly bent directions with β ≈ 90°.     

小掠射角下高斯谱粗糙海面反射损失建模

在散射能量基本为前向散射且集中在“镜面反射”方向的情况下,粗糙海面反射损失建模是声呐信号传播建模必不可少的一部分,尤其对于中远距离下浅海或者存在表面声道的水声环境,小掠射角(10°以内)下的粗糙海面反射损失建模尤为重要。首先基于高斯谱粗糙海面模型,通过高海况下的声传播试验数据处理分析了粗糙海面边界条件下的Ramsurf声传播模型的有效性,进而以Ramsurf声传播模型为基准,在小掠射角下,比较分析了Kirchhoff近似(KA)海面反射损失模型和小斜率近似(SSA)海面反射损失模型,数值计算结果表明,在小掠射角下SSA海面反射损失模型与Ramsurf计算结果较为吻合,是比较精确的海面反射损失模型。      

Behaviour of scattering from a rough surface at small grazing angles

The particular problem of wave scattering at low grazing angles is of great interest because of its importance for the long-distance propagation of radio waves along the Earth's surface, radar observation of near surface objects, as well as solving many other fundamental and applied problems of remote sensing. One of the main questions is: how do the scattering amplitude and specific cross section behave for extremely small grazing angles? We consider the process of wave scattering by a statistically rough surface with the Neumann boundary condition. This model corresponds to sound scattering from a perfectly 'hard' surface (for example, the interface between air and the sea surface) or 'vertically' polarized electromagnetic waves scattered by a perfectly conducting one-dimensional (i.e. cylindrical) surface when the magnetic field vector is directed along the generating line of this cylindrical surface. We assume that the surface roughness is sufficiently small (in the sense of the Rayleigh parameter) and the surface is rigorously statistically homogeneous and therefore, infinite. We confine ourselves only to the first-order approximation of small perturbation theory and therefore consider every act of wave scattering in the Born approximation when the Bragg scattering process takes place. Only one resonant Fourier component of surface roughness is responsible for the scattering in a given direction. However, we take into account the attenuation of incident and scattered waves due to the multiple scattering processes on the path 'before' and 'after' a scattering event in a given direction. Also we consider every one of these multiple scattering events only in the Born approximation. The main result we have obtained is that for small grazing angles the scattering cross section of the diffuse component decreases as the second power of the grazing angles with respect to the incident and scattered directions, and as the fourth power of the grazing angle for the backscattering (radar) situation. Generalizing our results from plane-wave scattering to finite beams allows us to obtain the criterion on the beamwidth. For sufficiently narrow beams the multiple scattering processes do not play any role because of a short 'interaction path', and only single Bragg scattering determines the scattering amplitude (which does not tend to zero for small grazing angles). However, for sufficiently wide beams the result obtained for infinite plane waves becomes valid: due to the above-mentioned multiple scattering processes, the scattering amplitude tends to zero for small grazing angles. Consequently, the behaviour of the scattering cross section for small grazing angles depends on the radiation pattern width of the transmitting and receiving antennae: for sufficiently wide beams the scattering cross section decreases to zero at small grazing angles, but for narrow beams it tends to the finite non-zero value.     

Elastic scattering of \sf{59.54}-keV \sf{\gamma}-rays in elements with \sf{22 \leq {Z} \leq {92}} at momentum transfer \sf{0.4 \leq {x} \leq 4.7~{\AA}^{\sf -1}}

Differential cross sections for elastic scattering of the 59.54 keV γ-rays in elements with 22 ≤Z ≤92 have been measured over the angular range 10^○–160^○corresponding to the momentum transfer 0.4 ≤x ≤4.7 Å^-1. The measurements at forward and backward angles were performed using the ²⁴¹Am radioactive point-source, target and the Ge detectors in the transmission and reflection arrangements, respectively. The measured differential scattering cross sections are compared with those based on the form-factor (FF) formalism and state-of-the-art S-matrix calculations to differentiate between their relative efficacies and to check angular-dependence of the anomalous scattering factors (ASF) incorporated as correction to the modified form-factor (MF). The S-matrix values exhibit agreement with the measured data at backward angles and differences ～10% at forward angles. The scattering cross sections based on the MF including ASF’s are in general lower at various angles by up to 20% for medium- and high-Z elements. The observed deviations being higher at the forward angles infer possibility of angular-dependence of ASF’s.     

In-plane bistatic backward scattering from seabottom with randomly inhomogeneous sediment and rough interface

1 Introduction Backward scattering of sound due to sediment is the main source of shallow waterreverberation. In order to predict the reverberation or detect sediment properties frommeasured reverberation data, a reasonable in-plane bistatic backward scattering (BBS)model is essential. The scattering can be caused by the roughness of water-sediment in-terface or by inhomogeneities within the volume of sediment. A great deal of researchhas been done on sediment backscattering, most of which h…     

Narrow states in38,40Ar via alpha +34,36S scattering

Excitation functions of the elastic scattering α+ ^34,36 S has been measured at beam energies E _α =12.56–15.00 MeV. Strongly fluctuating large cross sections in backward angles have been observed. Angular distributions were measured in the range θ _lab =98°–173° for fourteen energies, and many of them turned out to be dominated by one exclusive angular-momentum value, a behaviour typical for resonance scattering.     

Electron-atomic-hydrogen “elastic" scattering in the presence of a laser field

Laser-assisted electron-atomic-hydrogen “elastic" scattering is studied in the first Born approximation. The initial and final states of projectile electron are described by the Volkov wavefunctions; the dressed state of target described by a time-dependent perturbative wavefunction in soft photon approximation. The laser modified cross-sections are calculated in two distinct geometries for laser polarization either parallel or perpendicular to the incident direction of electron. The numerical results shows that the multiphoton cross-sections oscillate by a few orders over the whole scattering angular region. The results for a parallel geometry oscillate more frequently in the intermediate angles; while the results for a perpendicular geometry oscillate more frequently in the forward and backward angles. At large scattering angles, the sum rule of Kroll and Watson is noticeably violated. The laser modification on summed total cross-section increases with field strength, but decreases with field frequency and polarization deviation from the incident direction. Received 18 October 2001 and Received in final form 26 December 2001     

Boundary condition model for diffractive elastic scattering

Diffractive elastic scattering is studied by a boundary condition model that does not utilize a potential model.S-matrix elements are calculated and compared to those found from an optical potential model calculation. The unitarity of the model is related to the boundary condition imposed. A radially ingoing boundary condition is imposed on the wave function at one angle only, at a scattering angle of 180 °. This condition is required to hold in the vicinity of the nuclear radius, but not for all radii. Elastic scattering peaks at forward and backward angles are reproduced and discussed. The model is applied to composite particle scattering above the Coulomb barrier.     

含卷浪Pierson-Moscowitz谱海面电磁散射研究

海尖峰的存在会导致雷达虚警概率的上升和多目标环境中检测性能下降,因此研究海尖峰现象意义重大.海尖峰现象的一个重要特点是海面的水平极化散射强度接近甚至大于垂直极化散射强度,卷浪被认为是产生海尖峰的一个原因.首先建立了卷浪和Pierson-Moscowitz谱海面的共同模型,利用矩量法研究了卷浪模型的水平和垂直后向电磁散射特征,包括入射频率、入射角、风速和风向对电磁散射特征的影响.发现在小擦地角情况和较大风速下超级现象(水平散射强度大于垂直极化散射强度)比较明显,从而推论出在小擦地角入射下产生海尖峰现象的概率较大.同时对时变卷浪在小擦地角入射时的海杂波幅值分布特性和多普勒谱进行了分析.     

Semiclassical analysis of the scattering of 16O by 28Si

Semiclassical analysis of the optical potentials which fit the recent Stony Brook-BNL ¹⁶O + ²⁸Si scattering data, shows that the scattering mechanism of these potentials at backward angles is essentially the same. Neither the reflection from the sharp surface of the surface transparent potential used by Dehnhard and Shkolnik, Golin and Kahana, nor the modified form factor in the potential used by Lee and Chan is essential to fit the angular distribution. Based on the uniform approximation, we derive analytic formula to understand the angular distribution at backward angles and to understand the oscillatory structure in the 180° excitation functions.     

Elastic backward scattering of positive pions from 12C at 23, 29 and 35 MeV

The elastic scattering of positively charged pions at 23, 29 and 35 MeV scattering from ¹²C has been measured at 161°, 168° and 176° scattering angles. The new measurements give a backward descending behaviour to the existing angular distribution at 30 MeV. The complete angular distribution is compared to a calculation based upon the only Ericson-Ericson-Lorentz-Lorenz effect and to the theoretical models of Landau and Thomas and of Stricker et al. for low-energy pion-nucleus scattering.     

Elastic pp scattering at 1.463 GeV/c in the Coulomb interference region

The differential cross section for elastic pp scattering has been measured at 800 MeV, for laboratory angles ranging between 1.2° and 4.3° (lab). The ratio ? of the real to imaginary parts of the forward spin-independent scattering amplitude and the combined magnitudes of the forward double spin-flip amplitudes have been extracted from the data and are compared with the results of recent forward dispersion relation calculations and phase shift analyses.     

Differential cross sections of proton compton scattering at photon laboratory energies between 700 and 1000 MeV

Differential cross sections of proton Compton scattering have been measured at the Bonn 2.5 GeV synchrotron. 78 data points are presented as angular distributions at photon lab energies of 700, 750, 800, 850, 900, and 950MeV. The c.m. scattering angle ranges from 40°–130°, corresponding to a variation of the four momentum transfer squared betweent=?0.10 tot=?0.96 GeV² at 700 and 950 MeV, respectively. Two additional differential cross sections have been measured at 1000MeV, 35.6° and 47.4°. The angular distributions show forward peaks whose extrapolations to 0° are consistent with calculated forward cross sections taken from literature. The small angle data (|t| ?0.2 GeV²) together with the calculated cross sections at 0° are also consistent with the assumption of a slope parameterB of 5 GeV^?2. For the first time a rerise of the angular distributions towards backward angles has been observed. It becomes less steep with increasing energy. The most interesting feature of the angular distributions is a sharp structure which appears betweent=?0.55 GeV² at 700MeV andt=?0.72 GeV² at 950 MeV. Such a rapid varation of the differential cross section witht has never been ovserved in elastic hadron-hadron scattering or photoproduction processes. It indicates the existence of a dynamical mechanism which could be a peculiarity of Compton scattering.     

The NIMO Monte Carlo model for box-air-mass factor and radiance calculations

A new fully spherical multiple scattering Monte Carlo radiative transfer model named NIMO (NIWA Monte Carlo model) is presented. The ray tracing algorithm is described in detail along with the treatment of scattering and absorption, and the simulation of backward adjoint trajectories. The primary application of NIMO is the calculation of box-air-mass factors (box-AMFs), which are used to convert slant column densities (SCDs) of trace gases, derived from UV–visible multiple axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements, into vertical column densities (VCDs). Box-AMFs are also employed as weighting functions for optimal estimation retrievals of vertical trace gas profiles from SCDs. Monte Carlo models are well suited to AMF calculations at high solar zenith angles (SZA) and at low viewing elevation angles where multiple scattering is important. Additionally, the object-oriented structure of NIMO makes it easily extensible to new applications by plugging in objects for new absorbing or scattering species. Box-AMFs and radiances, calculated for various wavelengths, SZAs, viewing elevation and azimuth angles and aerosol scenarios, are compared with results from nine other models using a set of exercises from a recent radiative transfer model intercomparison. NIMO results for these simulations are well within the range of variability of the other models.     

Electromagnetic propagation in a curved two-dimensional waveguide

Abstract

Fields due to an electromagnetic wave propagating in a long irregular two-dimensional waveguide are calculated efficiently, using the method of left-right splitting to solve the coupled integral equations. Results are compared with those obtained from independent ray-theoretic calculations and give very close agreement. The approach has previously been applied to rough surfaces at low angles of incidence; here it is found to converge rapidly for surface slopes of 30°, and after a few iterations for incident angles up to 60° from grazing.     

Polarimetric weak-localization effect in scattering of natural light in the region of small phase angles

Results of laboratory measurements and interpretations of the polarimetric effect of weak localization (negative polarization) appearing under scattering of natural light by a dark ultradisperse surface (soot with albedo of 2.5%) are presented. The measurements were carried out in red light in a range of phase angles of 0.2°–4.2°. It was revealed that the soot, despite the low albedo, shows the polarimetric weak-localization effect inherent in bright surfaces such as the surface formed by smoked MgO. The results of measurements are interpreted using numerical simulation of multiple light scattering in a medium consisting of particles whose characteristics are close to those observed for soot. As the result of simulation, it was found that the scattering with the multiplicity exceeding two can give rise to a negative polarization branch, which becomes narrower with increasing scattering order. For the case of soot, four orders of scattering is sufficient to describe the observed polarimetric effect of weak localization with a necessary accuracy.     

Angular scattering diagrams of linearly polarized relativistic-intensity electromagnetic radiation in a plasma

Instability of the propagation of nonlinear nonmonochromatic relativistic-intensity electromagnetic waves in a cold subcritical-density plasma is analyzed in three-dimensional geometry. Angular diagrams of their scattering are presented. The calculations show that forward and backward scattering may occur. The radiation in a specific direction is a set of harmonics, propagating against a continuum background, whose frequencies depend on the angle. Radiation at a specific frequency propagates in a set of scattering cones. The azimuthal cone angles depend on frequency. Zh. éksp. Teor. Fiz. 116, 1947–1962 (December 1999)