植被冠层3D辐射传输模型及热辐射方向性模拟

研究了植被冠层的热辐射方向性并建立了有关模型.从辐射传输机理出发,建立了3D冠层场景,并将场景以微分体元方式进行离散,根据给定的观测几何参数进行逐个体元内部与体元之间的多次散射及发射辐射传输计算,最终通过积分运算得到所有微分体在半球空间上对给定观测方向上的热辐射,得出整个冠层的热辐射方向性.利用两个时相的地面观测数据对3D辐射传输模型及模拟结果进行了验证和分析,相关系数分别为0.91和0.79,RMSE分别为0.4K和0.6K,证明建立的模型是有效的,能改进热红外温度反演精度和实现组分温度反演.     

Temporal Mueller matrix solution for polarimetric scattering from inhomogeneous random media of nonspherical scatterers

Polarimetric scattering from inhomogeneous random media of nonspherical scatterers under a pulse incidence is studied. The time-dependent Mueller matrix solution of vector radiative transfer for layering random media is derived. Copolarized and cross-polarized bistatic and back- scattering are numerically calculated. The shape and intensity of polarized echoes well depict the inhomogeneous fraction profile of random scatterers. Its functional dependence upon the fraction profile, layering thickness, and other parameters are discussed. This technique is applicable to reconstruction of inhomogeneous fraction profile and inversion of the media thickness.     

The optical scatter channel

The scatter fields experimentally observable at the image plane of an optical receiver are modeled in a way that is consistent with the concepts and notations of both radiative transfer theory and the probability-computing receiver. Transient response and Doppler effect are considered. Single-particle scattering and its relationship to multiple scatter as treated by radiative transfer theory are reviewed. The statuses of experimental data and a variety of approximate methods for predicting the channel are also discussed.     

A 3-D polarized reversed Monte Carlo radiative transfer model for Millimeter and submillimeter passive remote sensing in cloudy atmospheres

This paper introduces a three-dimensional (3-D) polarized radiative transfer model that has been developed to assess the influence of cirrus clouds on radiances measured by the Earth Observing System Microwave Limb Sounder (EOS-MLS) instrument. EOS-MLS is on the Aura satellite, which launched in July 2004. The radiative transfer model uses a reversed Monte Carlo algorithm and has been incorporated in the Atmospheric Radiative Transfer Simulator 1.1.x software package. The model will be used to study aspects of the scattering problem that are not considered in the existing operational EOS-MLS cloudy-sky forward model, including the influence of nonspherical, oriented hydrometeors, and 3-D inhomogeneous cloud structure. This paper presents the radiative transfer algorithm and example model results, which demonstrate significant 3-D and polarization effects. Although the development of this model was motivated by the EOS-MLS mission, it is also directly applicable to ground-based and down-looking geometries.     

非线性各向异性散射介质红外传输特性的PN方法

针对含粒子参与性介质内红外辐射传输与光谱特性开展了数值方法研究.推导了辐射传输方程的球谐函数(PN-Approximation)分解形武,建立了求解非线性各向异性散射介质内红外传输的任意阶PN方法.基于辐射一导热耦合换热模型,通过已有理论解验证了高阶PN方法的计算精度.经验证,对于非线性各向异性散射问题,文章建立的任意...     

A Study of Backscattering and Emission from Closely Packed Inhomogeneous Media

The effects of close spacing between small scattering spheres were examined by keeping the distance-dependent terms in the expressions for the transverse scattered fields. The phase matrix was then derived from these fields and was used in the radiative transfer formulation to model scattering and emission from a densely populated, inhomogeneous layer. Computed results were compared with those obtained when the phase matrix was specialized to the far-field condition. It was found that the use of the far-zone condition tended to underestimate both the level of the copolarized backscattering and the cross-polarized backscattering. In emission computations, the use of the far-zone condition overestimated the level of the brightness temperature. hese effecit decreased with a decrease in the volume fraction or an increase in the exploring frequency, as expected. An improvement on the snow parameter (density and crystal size) estimation was shown to be possible when this new phase matrix was used.     

薄片激光器低畸变冷却技术研究

薄片激光器的导热距离短,能显著降低热透镜效应,已经成为高功率固体激光研究的热点。然而,随着泵浦口径和泵浦功率的不断增大,热效应愈发严重,其造成的热致畸变成为限制激光器出光功率和光束质量的主要因素之一。针对大尺寸薄片激光器工作时热致畸变过大的情况,提出了基于非均匀冷却的微通道复合射流冲击的流道设计思路。基于该思路完成了中心辐射结构冷却器的设计,并借助流-固-热耦合仿真,研究了不同冷却器的流道结构参数对增益介质热致畸变的影响。实验结果表明,采用中心辐射结构的冷却器能将相同条件下的增益介质的光学畸变缩小50%。     

Applications of dense media radiative transfer theory for passivemicrowave remote sensing of foam covered ocean

The effect of the foam covered ocean surface on the passive microwave remote sensing measurements is studied based on the electromagnetic scattering theory. In formulating an electromagnetic scattering model, the authors treat the foam as densely packed sticky air bubbles coated with thin seawater coating. The layer of foam covers the ocean surface that has air bubbles. They then use dense media radiative transfer (DMRT) theory with quasi-crystalline approximation (QCA) for densely distributed sticky moderate size particles to calculate the brightness temperatures of the foam-covered ocean surface. Results are illustrated for 19 GHz and 37 GHz and for both vertical and horizontal polarizations as a function of foam microstructure properties and foam layer thickness. Comparisons are also made with experimental measurements     

The 3-D multidomain pseudospectral time-domain method for wideband simulation

A three-dimensional (3-D) multidomain pseudospectral time-domain (PSTD) method with a well-posed PML is developed as an accurate and efficient solver for Maxwell's equations in conductive and inhomogeneous media. The curved object is accurately treated by curvilinear coordinate transformation. Spatial derivatives are obtained by the Chebyshev collocation method to achieve a high-order accuracy. Numerical results show an excellent agreement with solutions obtained by the FDTD method under fine sampling.     

One-dimensional variational retrieval algorithm of temperature, water vapor, and cloud water profiles from advanced microwave sounding unit (AMSU)

The measurements from satellite microwave imaging and sounding channels are simultaneously utilized through a one-dimensional (1-D) variation method (1D-var) to retrieve the profiles of atmospheric temperature, water vapor and cloud water. Since the radiative transfer model in this 1D-var procedure includes scattering and emission from the earth's atmosphere, the retrieval can perform well under all weather conditions. The iterative procedure is optimized to minimize computational demands and to achieve better accuracy. At first, the profiles of temperature, water vapor, and cloud liquid water are derived using only the AMSU-A measurements at frequencies less than 60 GHz. The second step is to retrieve rain and ice water using the AMSU-B measurements at 89 and 150 GHz. Finally, all AMSU-A/B sounding channels at 50-60 and 183 GHz are utilized to further refine the profiles of temperature and water vapor while the profiles of cloud, rain, and ice water contents are constrained to those previously derived. It is shown that the radiative transfer model including multiple scattering from clouds and precipitation can significantly improve the accuracy for retrieving temperature, moisture and cloud water. In hurricane conditions, an emission-based radiative transfer model tends to produce unrealistic temperature anomalies throughout the atmosphere. With a scattering-based radiative transfer model, the derived temperature profiles agree well with those observed from aircraft dropsondes.     

基于MODIS红外通道的辐射传输计算

通过建立地气系统的红外辐射传输方程,基于MODIS红外通道进行辐射传输计算.利用快速精确的透过率模型PFAAST计算大气透过率,在红外辐射传输计算中考虑了地面反射大气辐射亮度的影响,指出地面反射大气辐射亮度在整个方程所占比重随着地表发射率变小而增加,其中MODIS第33通道对发射率的改变最为敏感,美国标准大气下,当发射率ε=0.65时,比重达到7.12%,因此,忽略地面反射大气辐射亮度,直接影响红外辐射传输计算的准确性.模拟了MODIS各红外通道辐射亮度,并与MODTRAN4.0模拟结果比较,相对误差不超过0.12%,模拟了大气倾斜路径对卫星红外通道观测亮温的影响.     

Multidomain pseudospectral time-domain simulations of scattering by objects buried in lossy media

A multidomain pseudospectral time-domain (PSTD) method with a newly developed well-posed PML is introduced as an accurate and flexible tool for the modeling of electromagnetic scattering by 2-D objects buried in an inhomogeneous lossy medium. Compared with the previous single-domain Fourier PSTD method, this approach allows for an accurate treatment of curved geometries with subdomains, curvilinear mapping, and high-order Chebyshev polynomials. The effectiveness of the algorithm is confirmed by an excellent agreement between the numerical results and analytical solutions for perfectly conducting as well as permeable dielectric cylinders. The algorithm has been applied to model various ground-penetrating radar (GPR) applications involving curved objects in a lossy half space with an undulating surface. This multidomain PSTD algorithm is potentially a very useful tool for simulating antennas near complex objects and inhomogeneous media.     

基于辐射换热理论研究水雾对红外辐射测温仪的影响

从辐射、吸收或散射性参与介质的辐射换热机理出发,通过建立有参与性介质影响时辐射测温问题的物理模型与数学模型,探讨了当高温物体表面被水雾遮盖时,采用单色,比色红外辐射测温仪进行温度测量时所受到的影响.参与性介质影响下辐射测温问题的数学模型主要包括介质辐射换热模型和辐射测温仪模型.模型求解中水雾的辐射特征由Mie散射理论求解,考虑到辐射测温仪的工作特性,采用在波带上积分的方法处理水雾随光谱变化的辐射特性,并采用离散坐标法求解谱带辐射传递方程.研究表明,水雾粒子介质的粒度分布情况及辐射测温仪工作波长是测温体系的两个重要的影响因素.受到水雾介质的衰减作用,单色辐射测温仪的测量值小于真实值,比色测温仪的测量值则随着工作波长的不同可能比真实值偏大,也可能偏小.     

不稳定腔的频谱分析(续)

一、具有非均匀介质不稳定腔的频谱分析 根据[1]可知,光在不稳定腔中的振荡可以等效于在一个透镜序列中的传输问题来进行处理。具有非均匀介质的不稳定腔也可以用这样的方法来处理,所不同的是把[1]中的光阑函数     

星载微波ERS-1和多通道SSM/I观测冰雪的相关性和多层随机介质的数值模拟

该文研究了星载微波ERS－1散射计和多通道SSM／I辐射计在格陵兰岛、西伯利亚和阿尔卑斯山等地观测到的后向散射和热辐射数据，论证了同一地区同一时间段内ERS主动散射计和SSM／I被动辐射计观测数据的相关性。用冰雪覆盖区域的主被动遥感数据的比较，阐述了主被动联合多通道分析方法有利于监视和分析复杂地表在时间和空间尺度上的变化。该文用多层强起伏随机介质的后向散射模拟ERS数据，用多层密集散射粒子介质的辐射传输模拟SSM／I数据。讨论了后向散射与热辐射数值模拟结果的相关性，以及与星载微波遥感器实际观测结果的比较。     

Temperature-dependent excitonic absorption in long-period multiple In<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>As/GaAs quantum well structures

Temperature variations in the fundamental absorption edge of long-period In _x Ga_{1 − x} As/GaAs structures are studied for samples with different numbers of quantum wells and similar periods. The quantum wells were close in composition and width. Experimental data are interpreted in the model of exciton-polariton light transfer involving localized excitons in confined structures with a finite number of quantum wells. The experimentally observed low-temperature anomaly of the integrated absorption coefficient is attributed to reemission of resonance localized excitons along a finite chain of quantum wells, with no excitonic transfer. The radiative decay time of an exciton in a single quantum well is estimated from the experimental data. It is demonstrated that, at low temperatures, the major contribution to the width of the experimentally observed absorption line corresponding to the ground heavy-hole exciton state is made by inhomogeneous broadening of the line by the field of potential fluctuations associated with the compositional disorder of the alloy. At low temperatures, the inhomogeneous broadening is much more pronounced than the broadening governed by the true radiative and nonradiative dissipative decay.     

Electrical modeling of interface roughness in thin filmelectroluminescent devices

If two dielectric materials with different permittivities are in contact with each other and the interface between them is rough, then the electric field near this interface will be very inhomogeneous. In thin film electroluminescent devices, light is generated when electrons move back and forth in the phosphor layer under the influence of a strong ac electric field. At high electric fields, the electrons trapped in deep states at the interface between phosphor and insulator layer tunnel into the conduction band of the phosphor. This tunnel process is very sensitive to the electric field at the interface, so for a rough interface the electron flow will be very inhomogeneous. The relation between the interface roughness and the inhomogeneous charge transfer in thin film electroluminescent devices is investigated, based on an analytical flux tube model. The importance of the inhomogeneous current for the use of gray levels and aging is discussed     

Brightness Temperatures of Snow Melting/Refreezing Cycles: Observations and Modeling Using a Multilayer Dense Medium Theory-Based Model

The ability of electromagnetic models to accurately predict microwave emission of a snowpack is complicated by the need to account for, among other things, nonindependent scattering by closely packed snow grains, stratigraphic variations, and the occurrence of wet snow. A multilayer dense medium model can account for the first two effects. While microwave remote sensing is well known to be capable of binary wet/dry discrimination, the ability to model brightness as a function of wetness opens up the possibility of ultimately retrieving a percentage wetness value during such hydrologically significant melting conditions. In this paper, the first application of a multilayer dense medium radiative transfer theory (DMRT) model is proposed to simulate emission from both wet and dry snow during melting and refreezing cycles. Wet snow is modeled as a mixture of ice particles surrounded by a thin film of water embedded in an air background. Melting/refreezing cycles are studied by means of brightness temperatures at 6.7, 19, and 37 GHz recorded by the University of Michigan Truck-Mounted Radiometer System at the Local Scale Observation Site during the Cold Land Processes Experiment-1 in March 2003. Input parameters to the DMRT model are obtained from snow pit measurements carried out in conjunction with the microwave observations. The comparisons between simulated and measured brightness temperatures show that the electromagnetic model is able to reproduce the brightness temperatures with an average percentage error of 3% (~8 K) and a maximum relative percentage error of around 8% (~20 K)     

Scattering from a Layered Medium Connected with Rough Interfaces: Matrx Doubling Method

A theoretical scattering model is developed that computes the scattered and transmitted intensities from an inhomogeneous layered medium above the half-space. A matrix doubling method technique is extended to handle multilayer scattering problems of which each scattering layer of spherical particles has rough boundary interfaces. Incoherent scattering is assumed in the formulation so that the Stokes vector representations are used to calculate the polarimetric multiple scattering effects. The scattering coefficients are computed for a two-layered Rayleigh scattering medium with a rough boundary. The developed scattering model of a radiative transfer approach is useful for scattering computations dealing with a random medium often encountered in active and passive microwave remote-sensing problems.     

Amplification of terahertz radiation in a plasmon <Emphasis Type="Italic">n–i–p–i</Emphasis> graphene structure with charge-carrier injection

The absorption/amplification spectrum of terahertz radiation in inhomogeneous graphene (n–i–p–i structure) with a periodic dual metal grating is theoretically investigated. It is shown that the amplification of terahertz radiation sharply increases at the plasmon-resonance frequency, when losses due to electron scattering and emission are balanced by the plasmon gain (related to the stimulated radiative interband recombination of electron–hole pairs in the inverted region of graphene).