Measurements for profiles of aerosol extinction coefficient,backscatter coefficient,and lidar ratio over Wuhan in China with Raman/Mie lidar

<正>The profiles of aerosol extinction,backscatter coefficient,and lidar ratio in the lower troposphere over Wuhan are measured by a multi-channel Raman/Mie lidar.Using the lidar ratio retrieved by Raman scattering principle,the profiles of aerosol extinction and backscatter coefficients are also retrieved by Mie scattering signals,without a prior assumption about their relation in the traditional pure Mie signals data analyses.The observations by both Raman and Mie are in good agreement with each other.The high coherence shows that the system is reliable,and the Mie and Raman channels are in good adjustment and have the same field of view.     

青藏高原对流层气溶胶的激光雷达监测与研究

运用激光雷达方程和Fernald方法,对西藏那曲地区和北京地区对流层气溶胶的微脉冲激光雷达(MPL)探测数据进行时空反演和比较,结果表明:气溶胶散射比廓线有着较为相似的结构分布,分层锯齿结构非常明显,主要包括贴地层、气溶胶混合层和气溶胶对流层。那曲测站上空气溶胶散射比在无云条件下最大值基本上保持在2.0左右;在测站上空均存在密度较大且较厚的积云;夏季的混合层或残留层(浅蓝色部分)高度抬高;夏季对流层低层积云的云量和积云出现的概率较冬季要少。     

Dependence of the lidar signal depolarization on the receiver’s field of view in the sounding of fog and clouds

We report an experimental study of the lidar signal depolarization as a function of the relative contribution of the multiple scattering in case of optically dense objects in the atmospheric planetary boundary layer. Results of the observation of fog and stratus clouds are presented, as well as those obtained by sounding of stratocumulus clouds during a snowfall. The lidar data point to a rise of the depolarization coefficient as the influence of the multiple scattering increases in consequence of both viewing angle enlargement and penetration into the object sounded. The variations of the depolarization coefficient are studied as a function of the field of view. In the case of fog, this dependence is approximated by a three-parameter exponential law; it is found that the depolarization increases steeply when the viewing angle is increased from 9 mrad to 12.5 mrad. The relationships between the approximation parameters and the microphysical characteristics of the scattering medium are considered. The experimentally determined size of the area where multiple scattering occurs is in good agreement with that calculated according to the diffusion model. The results obtained on the multiple scattering effect on the depolarization can also be employed in determining the extinction coefficient profiles in optically dense objects, as well as in evaluating the characteristic size of the scattering particles. Received: 6 September 1999 / Revised version: 7 February 2000 / Published online: 6 September 2000     

小型米散射激光雷达的研制及其探测

介绍了一台自行研制的用于大气气溶胶光学特性和水平能见度测量的小型米散射激光雷达系统,并进行了一系列观测实验和分析.系统选用532nm波长激光作为光源,采用Fernald反演算法对接收到的大气回波信号进行反演得到气溶胶消光系数.通过对西安城区上空的气溶胶光学特性进行连续观测,测得了西安城区不同时刻消光系数的高度分布廓线、以及24小时内大气边界层高度的时空变化特性,并对大气水平能见度进行了连续观测,其结果与当地气象部门提供的水平能见度数据的变化趋势基本一致.观测结果表明,利用该米散射激光雷达可以对大气气溶胶光学特性和水平能见度进行有效测量.     

Inversion of neutron reflection data

A method is proposed for determining surface profiles from neutron reflection data by inversion. With the reflectivity and the dwell time regarded as measured input, the complex reflection coefficient is determined in the form of a rational function of the neutron momentum, for which the scattering potential is known in analytic form. A numerical example is given.     

An algorithm to determine cirrus properties from analysis of multiple-scattering influence on lidar signals

A Monte Carlo-based evaluation of the multiple-scattering influence on ground-based Raman lidar measurements is presented. The lidar returns from cirrus clouds are analyzed in order to evaluate vertical profiles of the extinction and backscattering coefficients. Results show that for the typical cirrus cloud, the presence of the multiple scattering can lead to an underestimation of the extinction coefficient by as large as 200% whereas the backscattering coefficient is almost unaffected for the Raman lidar technique. An algorithm to select one or a set of phase functions which fit to the lidar data is also presented. It is an iterative procedure based on Monte Carlo scattering simulation. By comparison of the experimental value of the lidar ratio, corrected for the multiple scattering influence, and the phase function used in the Monte Carlo simulation, one can determine a suitable phase function. The validity and sensitivity of the algorithm have been demonstrated by applying it to simulated cases. The application to some real cases indicates that our procedure allows for the establishing of a practical scattering model for the cirrus clouds.     

An inverse radiative transfer problem of simultaneously estimating profiles of temperature and radiative parameters from boundary intensity and temperature measurements

A parallel-plane space filled with absorbing, emitting, isotropically scattering, gray medium is studied in this paper. The boundary intensity and boundary temperature profiles are calculated for the inverse analysis. For the simultaneous estimation of temperature, absorption and scattering coefficient profiles in the medium, the sum of residuals of boundary intensity and temperature after being weighted by a balance factor is minimized through using a Newton-type iteration algorithm and the least-squares method. To avoid over-updating for the parameters, the relative updating magnitude during the iteration process is constrained not to be >0.5. It is shown that the boundary intensity measurement alone is not enough to estimate simultaneously the temperature (source) and the radiative properties (both absorption and scattering coefficients) when the measurement data contain sensitive random errors. The boundary temperature measurement can serve as a necessary supplementation to the boundary intensity to make this kind of inverse radiative transfer problem resolvable. It was shown that a compensation relationship between absorption and scattering coefficients makes it difficult to fix them accurately. Parabolic profiles for the three parameters are used to validate the estimation method. When the optical thickness approaches 4.0, the results for the radiative properties are not acceptable, although the result for temperature profile is reasonable. This means the method needs further improvements.     

利用散射系数变化测量血糖浓度的研究

论述了血糖浓度变化与溶液的散射系数的关系。在浑浊介质中散射特性取决于散射粒子和溶剂的折射率的相对大小,在血液中葡萄糖浓度的改变会引起血液折射率的变化,从而使血液的散射系数发生改变,从理论上给出了血糖浓度变化时计算散射系数变化的公式,得出了散射系数和血糖浓度成正比的结论。进一步讨论了满足临床应用目标下,散射系数的相对变化的测量精度要达到4.8×10-4,而对于中国人的血液绝对测量精度要达到6.82×10-3mm-1。用双积分球实验验证了理论计算的正确性,使用牛奶作为浑浊介质测量其散射系数与糖浓度的关系,在不同波长下散射系数都随葡萄糖浓度改变而改变,且线性度可以达到0.95以上。由此可以得出结论,血糖浓度可以通过测量散射系数来得到。     

银川上空大气气溶胶光学特性激光雷达探测研究

小型米散射激光雷达是广泛使用的探测大气气溶胶光学特性的有效工具。作者研制了一台小型米散射激光雷达,并利用该激光雷达于2009年4月1日至4月10日期间对宁夏银川地区(北纬38°29′, 东经106°06′)上空的大气气溶胶光学特性以及时空分布进行了观测。系统选用532 nm波长激光作为光源,采用Fernald法对接收到的大气回波信号进行反演,得到了气溶胶消光系数的高度分布廓线及24 h内气溶胶消光系数相对浓度的时空变化特性;并对期间一次明显的沙尘天气进行了观测和分析。观测结果表明,该小型米散射激光雷达能够对大气气溶胶及其时空分布情况进行有效、连续的观测,其观测结果有利于分析该地区气溶胶及沙尘天气的变化趋势。     

一维带限Weierstrass分形分层地面与矩形截面导体柱复合电磁散射FDTD研究

运用时域有限差分方法研究一维带限分形分层粗糙地面与矩形截面导体柱的复合电磁散射,计算复合电磁散射的双站散射系数,得到复合散射系数随散射角的变化,讨论粗糙面高度起伏均方根、分维、中间层介质、下层介质及矩形截面导体柱的参数等对复合散射系数的影响.     

Spectral line-shapes and moment analysis in isotropic and anisotropic light scattering spectra for gaseous argon

For direct comparison with the measurements of isotropic and anisotropic collision-induced light scattering spectra of argon gas at room temperature performed by Le Duff's group, quantum mechanical lineshapes are computed using different models of the interatomic potential and models of the diatom polarizability tensor invariants as input. New empirical trace and anisotropy parameters, consistent with the spectroscopic measurements, are thus obtained for the argon gas. These are compared, where possible, with existing computations based on classical physics, utilizing the first few even moments of the isotropic and anisotropic light scattering spectra. Some discrepancies with experiment, specially for the second Kerr coefficient, are found, but overall the agreement is satisfactory and the profiles calculated with these models coincide with experiments.     

Estimation of Rayleigh scattering loss in a double-clad photonic crystal fiber

In this paper the effect of photonic crystal fiber’s structure parameters on Rayleigh scattering was investigated. Rayleigh scattering loss (RSL) has been numerically estimated by average Rayleigh scattering coefficient based on the empirical relations for \(V\) and \(W\) parameters of double-clad photonic crystal fibers (DC PCFs). The dependence of RSL on the two structural parameters—the air hole diameter and the hole pitch was demonstrated. We have shown that RSL depends on the index profiles because of the different optical power confinement factors in every layer of DC PCF. Using these results, the RSL can be optimized by adjusting the fiber parameters—air-hole diameter as well as the air-hole pitch.     

修正反射系数的Kirchhoff近似方法计算高斯起伏冰面三维声散射

针对随机起伏冰面的声散射计算问题,利用修正反射系数的Kirchhoff近似方法计算了高斯起伏冰面的三维声散射。在计算模型中引入了冰面局部统计平均反射系数的概念,将二维高斯起伏冰面的散射分为相干散射和非相干散射,分别得到两类散射成分的散射系数公式,计算了高斯起伏冰面三维声散射的散射强度。分析了散射强度与随机起伏冰面的均方根高度、声波入射角度及频率的关系。通过实验室水池中高斯起伏冰面的散射强度测量实验,对理论模型的计算结果进行了验证。将实验结果分别与采用冰面局部统计平均反射系数的模型计算结果和文献中采用平整冰面镜反射系数的模型计算结果进行了对比,采用冰面局部统计平均反射系数的模型计算结果与实验测量值吻合较好。      

A comparative study of electron and positron penetration in silicon dioxide

Many researches are devoted to the study of silicon dioxide, a material of great interest for its use in the micro-electronics industry. This paper aims to compare the behavior of electrons and positrons when impinging on silicon dioxide targets in order to investigate the differences and the similarities. In particular, the inelastic mean free path, the stopping power, the differential elastic scattering cross-section and the total and transport elastic scattering cross-section of electrons and positrons penetrating in silicon dioxide targets are compared in order to better understand their influence in determining the implantation profiles shapes, the mean range of penetration, the maximum range of penetration and the backscattering coefficient as a function of the primary energy of the incident particles.     

Effect of diffraction on stimulated Raman scattering of laser radiation in the middle atmosphere

The theoretical aspects of propagation of laser radiation along slanted paths in the atmosphere at high altitudes under conditions of stimulated Raman scattering (SRS) by molecular nitrogen are considered. The SRS power conversion coefficient, the transverse intensity distribution, and the effective size of laser beams with different initial spatial profiles are numerically simulated along the propagation path. The behavior of these parameters is studied for different ratios between the optical path length and the length of free diffraction of the initial laser beam. It is shown that, at a given level of the increment of the SRS amplification, the diffraction can both increase and decrease the efficiency of the Raman interaction of waves owing to the intensity redistribution in the transverse beam profile. This effect is the most pronounced for beams with non-Gaussian initial spatial intensity profiles.     

Adjacency Effect in the Atmospheric Correction of Satellite Remote Sensing Data: Evaluation of the Influence of Aerosol Extinction Profiles

In the atmospheric correction of satellite data in the visible and near-infrared bands, it is necessary to remove the adjacency effect due to the reflection from contiguous pixels. Evaluation of the influence of aerosol vertical distributions on the adjacency effect is done by calculating the single-scattering light intensity which, after the reflection at the ground surface, reaches the satellite sensor via a single scattering with a molecule or an aerosol particle. In the simulation, we assume aerosol vertical profiles similar to those used in the MODTRAN radiation transfer code, and those having a mixed layer with a uniform value of the aerosol extinction coefficient. We assume for the ground surface a simple model representing a border of land/sea surfaces. In spite of the single scattering approximation, it is confirmed that even if the optical thickness is the same, we have a larger adjacency effect when the extinction coefficient is large at higher altitudes. We also discuss the dependence of the adjacency effect on the aerosol optical thickness and that on the difference in the reflectances of the land and sea surfaces along the border.     

紫外域激光雷达探测西安城区上空大气气溶胶时空剖面

开发了一套紫外域波长的米散射激光雷达系统,探测西安城区上空大气气溶胶污染物质的光学特性及时空变化.系统选用对人眼较为安全的355 nm波长激光作光源,采用高光谱分辨率光栅,并借助光阑,将接收到的主要大气回波信号谱线（米散射和瑞利散射光谱与白天太阳背景光）从空间分离,剔除大部分太阳背景噪音,提高系统的白天探测能力.通过对西安城区上空的气溶胶时空变化特性进行24 h连续观测,采用Klett方法反演得到气溶胶消光系数,首次测得西安城区不同时刻消光系数的高度分布剖面图以及24 h内气溶胶相对质量密度的时空变化特性.     

On the contraction of the W(001)-(1 × 1) surface using LEED intensity analysis

Three recent independent attempts at deducing the W(001)-(1 × 1) surface structure by LEED beam intensity analysis have yielded contractions of the topmost layer spacing of 6 ± 6%, 11 ± 2%, 4.4 ± 3% normal to the surface plane. We investigate possible reasons for the discrepancies by comparing published experimental and theoretical profiles of these workers as well as our own. Our main conclusions are that the direct comparison of experimental data of different investigators shows deviations which are comparable to the changes in the calculated profiles for various surface contractions. Also the deviations between calculated intensity profiles using different (but still realistic) assumed scatteting potentials are comparable to the changes in the calculated profiles for various surface contractions. The main uncertainty in the scattering potential is the choice between the Slater free electron exchange-correlation term (coefficient α = 1) or the Kohn-Sham version ($\text{α =}\text{2}\text{3}$) or a value in between. For tungsten the corrections due to relativistic atomic scattering must also be considered. These uncertainties in the calculated and experimental profiles lead to the conclusion that the surface layer contraction of W(001)-(1 × 1) is not known at the present time. To assess the potential of LEED in deducing surface structures of this type further comprehensive analyses are required where the uncertainties in the theoretical scattering potential are also examined.     

Optical Properties of Human Eye Cataractous Lens in vitro in the Visible and Near-IR Ranges of the Spectrum

Optics and Spectroscopy - The spectral dependences of the absorption coefficient, scattering coefficient, scattering anisotropy factor, and transport scattering coefficient for human eye lens in...     

海面冰层对声波的反射和散射特性

北极海面冰层复杂多变,其对声波的反射和散射严重影响冰下水声信道的传输特性,建立海面冰层的声波反射和散射模型对冰下水声通信研究具有重要意义.假设海面冰层为多层固体弹性介质且冰-水界面粗糙,满足微扰边界条件,导出声波从海水介质入射到海面冰层时相干反射系数满足的线性方程组.对相干反射系数随声波频率、掠射角、冰层厚度的变化进行数值分析.进一步引入根据散射声场功率谱密度计算散射系数的方法,改变掠射角,对冰层厚度、散射掠角对散射系数的影响进行研究.