基于积分球试验的粉体材料辐射特性分析研究

为了获取准确的粉体材料红外辐射特性参数,本文对Al_2O_3粉体材料的红外辐射特性进行了以下研究:对粉末样品进行积分球反射率和透射率的测量试验,利用三热流近似法求解辐射传输方程,结合粒子群算法反演粉末的散射系数和吸收系数。Al_2O_3粉体材料的辐射特性研究结果显示,在4~7μm波段散射系数和吸收系数均随波长和厚度的增加而减小,且粉末层厚度越小,粒子散射越强烈。该方法适用于获取常温下各种粉体材料的辐射特性参数,并分析粉体材料的辐射特性参数及其与厚度等因素的关系。     

一维平板内介质和表面的辐射特性参数同时反演方法EI北大核心CSCD

考虑了实际物体表面BRDF的影响,利用方向半球反射率、方向半球透射率、法向反射率和法向透射率等光谱数据,同时反演了一维平板内介质和表面的辐射特性参数。将该方法用于吸收散射、强散射和强吸收三种介质的辐射特性参数反演,反演结果与给定初值较吻合。     

一维平板内介质和表面的辐射特性参数同时反演方法

考虑了实际物体表面BRDF的影响,利用方向半球反射率、方向半球透射率、法向反射率和法向透射率等光谱数据,同时反演了一维平板内介质和表面的辐射特性参数。将该方法用于吸收散射、强散射和强吸收三种介质的辐射特性参数反演,反演结果与给定初值较吻合。     

半透明介质场参数的非接触测量算法研究

本文在考虑半透明介质吸收、发射以及散射衰减作用的情况下采用视在光线法计算某探测方向上介质边界出射辐射强度分布作为逆问题的输入数据,采用LSQR方法在介质辐射特性参数已知情况下重建介质三维温度分布,重建结果显示,无论有无测量误差存在,利用LSQR方法都可以在已知辐射特性参数的条件下很好地重建出介质的三维温度场。在此基础上提出LSQR-SPSO混合算法,并应用于同时重建三维温度场及辐射特性参数(吸收系数、散射系数)。计算结果显示,无论有无测量误差存在,利用LSQR-SPSO混合算法都可以很好地同时重建出介质的吸收系数、散射系数及三维温度场,相比较而言,介质的温度场更容易被重建出来。     

半透明平板边界入射辐射热流密度的反问题

对一维半透明平板内辐射、导热及边界对流耦合换热过程进行了研究。提出了一种由一侧边界出射辐射强度反演另一侧边界入射辐射热流密度的方法。通过对各向异性散射、吸收系数、散射系数、边界外侧来流温度、对流换热系数、半透明平板的导热系数和平板厚度等参数对反演精度影响的分析表明,方法是可行的。     

基于光角度散射法的弥散介质多种辐射参数联合反演研究

本文基于光角度散射法,对弥散介质多种辐射特性参数进行了联合反演。此外,本文还提出了一种基于敏感度分析和主成分分析的测量角度优化筛选方案,用以寻找反演精准度较高的测量角度。研究表明:采用角度散射法对弥散介质多种辐射特性测量参数进行联合反演时,对于前向散射占优或者后向散射占优弥散介质,优化测量角度范围分别推荐为(0°,40°]和[140°,180°);与随机测量角度相比,优化筛选的测量角度能确保反演结果精度,且在5%的随机测量误差下,仍能获得合理的反演结果。     

吸收性介质内气泡的表观辐射特性研究

气泡的存在对介质的辐射传输特性具有重要影响。本文基于广义MIE理论计算了气泡在吸收性介质内的辐射特性。研究了介质的复折射率虚部对气泡表观辐射特性的影响以及0.2~200μm可见光及红外波长范围内介质水的吸收特性对气泡粒子系散射系数和吸收系数的影响。结果表明,随着粒子尺度参数的增大,介质吸收对气泡表观辐射特性的影响相应增大,忽略介质吸收将带来很大误差;当波长大于2μm时,介质水的吸收特性对气泡的散射特性影响不能忽略。     

基于光学相干层析成像技术的强散射介质光学特性测量

利用光学相干层析成像技术对强散射介质的光学特性进行了测量研究.通过理论模拟分析了镜面反射条件下散射系数及各向异性因子对外差效应因子的影响.提出镜面反射情况下利用广义惠更斯菲涅尔模型提取材料光学特性的算法.通过对不同浓度的IntralipidTM溶液的测量,获得了可靠的光学散射特性实验结果,并研究了散射系数与其浓度之间的关系,拟合结果显示散射系数与IntralipiTM溶液浓度近似呈线性关系.     

基于光学相干层析成像技术的强散射介质光学特性测量

利用光学相干层析成像技术对强散射介质的光学特性进行了测量研究.通过理论模拟分析了镜面反射条件下散射系数及各向异性因子对外差效应因子的影响.提出镜面反射情况下利用广义惠更斯菲涅尔模型提取材料光学特性的算法.通过对不同浓度的IntralipidTM溶液的测量,获得了可靠的光学散射特性实验结果,并研究了散射系数与其浓度之间的...     

吸收散射性三维矩形介质内辐射源项的反问题

提出了一种由边界出射辐射强度反演吸收散射性三维矩形介质内辐射源项分布的方法。该方法是在辐射传递方程离散坐标近似的基础上,用求目标函数极小值的共轭梯度法进行反演计算。通过对介质辐射特性、光学厚度等参数对反演精度影响的分析,结果表明,即使存在测量误差,本文所提出的方法可较精确地反演辐射源项。     

Near-infrared radiative properties of porous zirconia ceramics

Infrared radiative properties of zirconia ceramics of porosity about 16% are studied by means of the measurements of directional–hemispherical reflectance and transmittance in the wavelength range from 2.5 to 9 μm. The recently suggested modified two-flux approximation is examined as a simplified basis of the identification procedure. A comparison with the exact numerical solution confirms a good accuracy of this approach for identification of the absorption coefficient of ceramics. An analysis of the results for transport scattering coefficient showed that scattering is determined by isotropic pores with characteristic average radius about 1 μm. The corresponding approximate theoretical model of radiative properties of ceramics is suggested. The absorption coefficient of bulk zirconia in the semi-transparency range is obtained from the data for porous zirconia ceramics.     

Maximum time-resolved hemispherical reflectance of absorbing and isotropically scattering media

This paper presents a parametric study of the time-resolved hemispherical reflectance of a plane-parallel slab of homogeneous, cold, absorbing, and isotropically scattering medium exposed to a collimated Gaussian pulse. The front surface of the slab is transparent while the back surface is assumed to be cold and black. The 1-D time-dependent radiation transfer equation is solved using the modified method of characteristics. The parameters explored include (1) the optical thickness, (2) the single scattering albedo of the medium, and (3) the incident pulse width. The study pays particular attention to the maximum transient hemispherical reflectance and identifies optically thin and thick regimes. It shows that the maximum reflectance is independent of the optical thickness in the optically thick regime. In the optically thin regime, however, the maximum hemispherical reflectance depends on all three parameters explored. The transition between the optically thick and thin regimes occurs when the optical thickness is approximately equal to the dimensionless pulse width. Finally, correlations relating the maximum of the hemispherical reflectance as a function of the optical thickness, the single scattering albedo of the materials, and the incident pulse width have been developed. These correlations could be used to retrieve radiation characteristics or serve as initial guesses for more complex inversion schemes accounting for anisotropic scattering.     

Modeling of light propagation in turbid medium using Monte Carlo simulation technique

The aim of the current study is to simulate the laser photon through biological tissue during PDT therapy using Monte Carlo simulation technique. The model is coded using MATLAB. Interaction of laser light with turbid medium e.g. human tissue depends on the optical properties of the medium i.e. refractive index n, absorption coefficient μ _a , scattering coefficient μ _s and anisotropy factor g. Laser light transport through tissue is governed by the radiative transport equations based on absorption and scattering. Direct sampling is used for step-size generation before interaction via absorption or scattering with the transmitting medium, for deflection and azimuthal angle (θ and ϕ) when the scattering even occurs. The tissue medium considered is divided into radial, axial and angular grid elements and an infinite narrow beam with normal incidence on the tissue is considered. The laser light absorbance inside the tissue, reflectance at the top boundary of the tissue and transmittance at the bottom are estimated and these quantities are shown varying radially and angularly. Results of reflectance, transmittance and fluence are compared with the already published results to confirm the authenticity of our coding and these results are found to lie at only 3–4% error.     

Accurate reconstruction of the optical parameter distribution in participating medium based on the frequency-domain radiative transfer equation

Reconstructing the distribution of optical parameters in the participating medium based on the frequency-domain radiative transfer equation(FD-RTE) to probe the internal structure of the medium is investigated in the present work.The forward model of FD-RTE is solved via the finite volume method(FVM). The regularization term formatted by the generalized Gaussian Markov random field model is used in the objective function to overcome the ill-posed nature of the inverse problem. The multi-start conjugate gradient(MCG) method is employed to search the minimum of the objective function and increase the efficiency of convergence. A modified adjoint differentiation technique using the collimated radiative intensity is developed to calculate the gradient of the objective function with respect to the optical parameters. All simulation results show that the proposed reconstruction algorithm based on FD-RTE can obtain the accurate distributions of absorption and scattering coefficients. The reconstructed images of the scattering coefficient have less errors than those of the absorption coefficient, which indicates the former are more suitable to probing the inner structure.     

基于瞬态辐射信号的各向同性散射均匀介质光学特性PSO反演

利用激光入射半透明介质时有限体积法（FVM）得到的时域反射和透射信号,结合标准微粒群（PSO）、随机微粒群（SPSO）和多相微粒群（MPPSO）三种不同的智能算法反演短脉冲激光辐照下各项同性散射均匀参与性介质的吸收系数和散射系数,结果表明三种微粒群算法都能够高效准确地反演均匀介质内的光学参数。     

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.     

On the finite volume method and the discrete ordinates method regarding radiative heat transfer in acute forward anisotropic scattering media

The ability of the finite volume method (FVM) and the discrete ordinates method (DOM) to model radiative heat transfer in acute forward anisotropic scattering media has been investigated. The test case involves a purely scattering medium in a cubic enclosure, irradiated by one boundary with diffuse emission. Four phase functions have been considered: three of the Henyey-Greenstein type with respective asymmetry factors of 0.2, 0.8 and 0.93, and a Mie phase function with a strong forward scattering peak (computed for a size parameter of 245 and corresponding to an asymmetry factor of 0.93). Results obtained with the FVM are in good agreement with Monte Carlo reference solutions, whatever the level of acute anisotropic scattering (for asymmetry factors up to 0.93). The DOM combined with the renormalization procedures of the phase function proposed by Kim and Lee (Effect of anisotropic scattering on radiative heat transfer in two-dimensional rectangular enclosures. Int J Heat Mass Transfer 1988;31:1711-21. [1]) and Wiscombe (On initialization error and flux conservation in the doubling method. JQSRT 1976;18:637-58. [2]) provides accurate results only for the smallest asymmetry factor. As the asymmetry factor increases, the renormalization procedures induce strong modifications in the values of the discretized phase function resulting in an underestimation of the effective attenuation by scattering. This error has been found to increase with optical thickness. In fact, when using the DOM, results would be more accurate combining this method with a Delta-Eddington approximation of the phase function, instead of using the actual phase function which is altered too much by renormalization.     

Inverse transient radiation analysis in one-dimensional non-homogeneous participating slabs using particle swarm optimization algorithms

Particle Swarm Optimization (PSO) algorithms, including standard PSO, Stochastic PSO, and Multi-Phase PSO, are applied to solve the time-domain inverse transient radiation problems in the present research. Time-resolved transmittance and reflectance signals of four different measuring models serve as the measurement data, which estimate absorption, scattering coefficients, and geometric position within one-dimensional non-homogeneous media by inverse simulation. To check retrieval performances and accuracies of PSO-based approaches, four different inverse transient radiation cases are investigated to deal with one homogeneous layer, two-layer, three-layer, and continuous non-homogenous media. The influences of different searching ranges, swarm sizes, and maximum fly velocities on the fitness function of PSO are discussed. Meanwhile, the effects of measurement errors on the reconstruction accuracy are also investigated. All the results confirm that radiative parameters could be estimated accurately with measurement noise using PSO-based approaches.     

Analysis of collimated radiation in participating media using the discrete transfer method

A general formulation of the discrete transfer method is provided to analyze radiative heat transfer problems in a participating medium subjected to collimated radiation. The formulation is validated by considering 1-D planar absorbing, emitting and anisotropically scattering gray medium in radiative equilibrium. Anisotropy of the medium is approximated by linear anisotropic phase function. For the purpose of comparison, the problem is also solved analytically. Results are obtained for different angles of incidence of the collimated radiation. At a given angle of incidence, results are obtained for forward, isotropic and backward scattering situations. Heat flux results are compared over a wide range of values of the extinction coefficient. Emissive power distributions in the medium are also obtained for some cases. The discrete transfer method results are found to compare very well with the analytic results.     

基于 PROSPECT模型的蔬菜叶片叶绿素含量和SPAD值反演

叶绿素含量是衡量植物营养和病虫害发生情况的重要指标。传统的分光光度法对植物叶片破坏性较大且无法实时、快速、无损地获取叶绿素含量。新兴的利用叶绿素仪测量叶绿素相对含量（以下简称SPAD值）的方法不能定量获取实际含量。光学辐射传输模型PROSPECT从生物物理、化学的角度以及能量传输的过程出发,定量描述了叶片色素、水分、结构参数等对叶片反射光谱的影响。因此,提出利用PROSPECT模型同时反演蔬菜叶片叶绿素含量和SPAD值,实时、快速、无损、定量获取植物叶片叶绿素的含量。第一,多次测量三种蔬菜叶片的反射光谱,并用叶绿素仪测量SPAD值。然后,预处理光谱数据,获得平均反射率光谱。第二,以欧式距离为评价函数,利用PROSPECT模型对实测反射率光谱进行拟合。拟合过程中三种蔬菜欧式距离最大为0.008 9,最小为0.006 4,平均为0.007 5,表明该模型能够很好地拟合蔬菜叶片的反射率光谱。第三,根据拟合结果,反演叶绿素含量和透射率光谱,再根据透射率光谱获取叶片在940和650 nm波长处的光透过率,计算叶片的反演SPAD值。第四,建立反演叶绿素含量、反演SPAD值与实测SPAD值的关系模型。结果表明: (1)利用该模型反演得到的叶绿素含量值与实测SPAD值有较好的线性关系, 其关系模型为：y=1.463 3x+16.374 3,两者相关系数为0.927 1,模型的决定系数为0.862,均方根误差为2.11;(2)利用该模型反演得到的SPAD值与实测SPAD值之间线性关系较好,其关系模型为：y=0.986 9x-0.668 3,两者相关系数为0.845 1, 模型的决定系数为0.714 3,均方根误差为3.380 2。研究表明,通过测量植物叶片的反射率光谱,利用PROSPECT模型可以无损、定量地获取蔬菜叶片的叶绿素含量和SPAD值。该方法可推广至其他植物的叶绿素测量和实时监测,为变量施肥、精准种植提供可靠的数据支持。研究结果对蔬菜生长态势的无损监测具有重要的意义。