基于大气辐射传输模型的地物偏振反射率反演方法

提出一种基于大气矢量辐射传输模型的地物偏振反射率反演方法.利用辐射传输模型,建立地表反射率、观测条件与传感器入瞳处辐亮度偏振态的查找表,再进行查找表反查及数值计算,完成偏振反射率反演.验证实验表明,典型地面目标物的偏振反射率反演精度可达到90%.     

非线性散射介质内辐射传递的积分矩方法

提出了求解非线性散射介质内辐射传递的积分矩方法.将辐射传递方程中散射相函数的积分项转化为辐射强度各阶矩的线性组合.散射相函数为勒让德多项式展开形式,辐射强度矩的最高阶数与散射相函数的展开项数相同.将原本复杂的积分微分方程转化为微分方程,通过积分法求解此方程.积分矩方法不需要对立体角进行离散,不会引起射线效应.积分矩方法...     

An overview of the AIRS radiative transfer model

The two main elements of the Atmospheric Infrared Sounder radiative transfer algorithm (AIRS-RTA) are described in this paper: 1) the fast parameterization of the atmospheric transmittances that are used to perform the AIRS physical retrievals and 2) the spectroscopy used to generate the parameterized transmittances. We concentrate on those aspects of the spectroscopy that are especially relevant for temperature and water vapor retrievals. The AIRS-RTA is a hybrid model in that it parameterizes most gases on a fixed grid of pressures, while the water optical depths are parameterized on a fixed grid of water amounts. Water vapor, ozone, carbon monoxide, and methane profiles can be varied, in addition to the column abundance of carbon dioxide.     

闭环光纤陀螺的建模方法

在设计基于光纤陀螺（FOG）的惯性测量单元之前,必须首先获得陀螺的传递函数模型,研究的目的就是寻求一种有效的FOG传递函数的辨识方法。本文分析了传统方法辨识闭环FOG传递函数的困难,然后提出了利用速率转台对地球自转角速度的调制分量作为陀螺输入来辨识FOG传递函数的方法,并设计了基于最小二乘法的正弦信号幅值和相位的检测方法。通过对国外某FOG模型的分析说明了该方法的可行性,并且该方法实施简单,能够克服白噪声对信号幅值和相位检测带来的影响。     

辐射传输方程中非对称因子的估算

非对称因子是辐射传输理论中一个十分重要的参数.基于Mie理论,对单分散系粒子单次散射的非对称因子进行了研究和计算.结果证实:在折射率实部一定情形下,非对称因子有确定的极限值,例如,实折射率为1.33时,该极限值为0.884 7;对实际大气而言,非对称因子一般不会超过0.8.对辐射传榆计算中非对称因子的取值对Mie像函数、H-G像函数和H-G*像函数的影响进行了比较,结果表明:在相同的非对称因子下,H-G*像函数更接近Mie散射像函数.     

辐射传输方程中的平均单次散射反照率的计算

根据米耶理论,对均匀系中单粒子平均单次散射反照率的计算进行了研究,并分析了反照率与粒子尺度因子以及复折射率之间的关系.结果表明,当粒子尺度因子x较小时,反照率随着x的增大而增大,但是当x再继续增大时,反照率出现了"波动",总体呈现出减小的趋势,最终趋于0.5.利用米耶理论和van de hulst近似,还分别计算0.4～0.5μm和8～12μm光谱范围内气溶胶粒子的反照率,并进行了比较,结果表明,除了波长为3μm的邻域外,随着波长的增大,反照率逐渐减小,但是利用van de hulst近似所计算的结果在8～12μm光谱范围内有较大的误差.     

Intercomparison of microwave radiative transfer models forprecipitating clouds

An intercomparison of microwave multiple scattering radiative transfer codes used in generating databases for satellite rainfall retrieval algorithms has been carried out to ensure that differences obtained from retrieval techniques do not originate from the underlying radiative transfer code employed for the forward modeling. A set of profiles containing liquid water and ice contents of cloud and rain water as well as snow, graupel and pristine ice were distributed to the participants together with a black box routine providing Mie single scattering, atmospheric background absorption and surface emissivity. Simulations were to be carried out for nadir and off-nadir (53.1°) observation angles at frequencies between 10 and 85 GHz. Among the radiative transfer models were two-stream, multiple stream and Monte Carlo models. The results showed that there were two major sources of differences between the codes. 1) If surface reflection/emission was considered isotropic, simulated brightness temperatures were significantly higher than for specular reflection and this effect was most pronounced at nadir observation and over ocean-type surfaces. 2) Flux-type models including delta-scaling could partially compensate for the errors introduced by the two-stream approximation. Largest discrepancies occurred at high frequencies where atmospheric scattering is most pronounced and at nadir observation. If the same surface boundary conditions, the same multiple-stream resolution and the same scaling procedures are used, the models were very close to each other with discrepancies below 1 K     

Design of distributed-element RF filters via reflectance data modeling

A reflectance-based modeling method is presented, to obtain the distributed-element counterpart of a lumped-element network, which is described by measured or computed reflectance data at a set of frequencies. Numerical generation of the scattering parameters forms the basis of this modeling tool. It is not necessary to select a circuit topology for the distributed-element model, which is the natural consequence of the modeling process. Our approach supplements the known interpolation methods by a simple technique that does not involve complicated cascaded circuit topologies and whose numerical convergence is proven. To illustrate the utilization of the proposed method, a lumped-element low-pass Chebyshev filter is transformed to its distributed-element counterpart. The filter, designed for a frequency band around 1 GHz, was fabricated and experimentally characterized. We find excellent agreement between measured and simulated transducer power gain over the entire frequency band.     

Invertible canopy reflectance modeling of vegetation structure insemiarid woodland

The Li-Strahler canopy reflectance model, driven by Landsat Thematic Mapper (TM) data, provided regional estimates of tree size and density in two bioclimatic zones in West Africa. This model exploits tree geometry in an inversion technique to predict average tree size and density from reflectance data using a few simple parameters measured in the field (spatial pattern, shape, and size distribution of trees) and in the imagery (spectral signatures of scene components). The model was tested in sparse woodland and wooded grassland in the Sahelian and Sudanian bioclimatic zones in West Africa     

偏振辐射传输的插值计算以及流数对计算结果的影响

根据平面平行大气中偏振辐射传输方程的求解,利用解析插值方法实现了对其空间任意一点(任意光学厚度、任意角度)偏振辐射的计算。使用了瑞利散射以及米散射对该程序进行验证,所得结果与Coulson和Stamnes的计算结果进行了比较,误差在0.7%以内。同时还分析了流数对计算结果的影响,通过比较半球8流时米散射的最大相对误差ηmax≤1.82%,平均相对误差ηaver=1.627%;并且该计算误差随着计算流数的增加越来越小,在24流时,计算结果比较稳定,误差最大值ηmax<1%,平均相对误差ηaver=0.223%。     

Simulation method of reflectance measurement error using the OTDR

This letter presents an algorithm relating two different optical time-domain reflectometer (OTDR) reflectance measurement methods. From the impulse response of an OTDR, and the attenuation and reflectance values of a reflective event supplied by the OTDR operating according to a first classical implemented method, the algorithm allows the determination of the reflectance that would be measured according to a second more accurate method. Over a 10-dB comparison range the deviations between experimental results and those obtained with the proposed algorithm do not exceed 0.5 dB     

Estimation of radiative heat transfer using a geometric human model

In order to provide a detailed estimate of radiative heat transfer between a human body and its surrounding environment, we have developed a geometric model of a human form and an algorithm. The model closely resembles the actual shape of a human body and is composed of small quadrilateral surfaces. Dealing with an object or a space with an arbitrary shape, the developed algorithm can judge efficiently whether there is an obstruction between a pair of surfaces. As a result, the angle factors between a pair of surfaces that only occur during radiative heat transfer can be defined. The distribution of the radiative heat transfer rates shows the characteristics of body shape and variations in posture.     

An analytic BRDF model of canopy radiative transfer and itsinversion

Radiative transfer modeling of the bidirectional reflectance distribution function (BRDF) of leaf canopies is a powerful tool to relate multiangle remotely sensed data to biophysical parameters of the leaf canopy and to retrieve such parameters from multiangle imagery. However, the approximate approaches for multiple scattering that are used in the inversion of existing models are quite limited, and the sky radiance frequently is simply treated as isotropic. This paper presents an analytical model based on a rigorous canopy radiative transfer equation in which the multiple-scattering component is approximated by asymptotic theory and the single-scattering calculation, which requires numerical integration to properly accommodate the hotspot effect, is also simplified. Because the model is sensitive to angular variation in sky radiance, the authors provide an accompanying new formulation for directional radiance in which the unscattered solar radiance and single-scattering radiance are calculated exactly, and multiple-scattering is approximated by the well-known δ two-stream approach. A series of validations against exact calculations indicates that both models are quite accurate, especially when the viewing angle is smaller than 55°. The Powell algorithm is then used to retrieve biophysical parameters from multiangle observations based on both the canopy and the sky radiance distribution models     

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.     

Evaluation of radiative transfer simulations over bright desert calibration sites

The Spinning Enhanced Visible and Infrared Imager (SEVIRI), the Meteosat Second Generation main radiometer, measures the reflected solar radiation within three spectral bands centered at 0.6, 0.8, and 1.6 /spl mu/m, and within a broadband. This broadband is similar to the solar channel of the radiometer onboard the first generation of METEOSAT satellites. The operational absolute calibration of these channels relies on modeled radiances over bright desert sites, as no in-flight calibration device is available. These simulated radiances represent, therefore, the "reference" against which SEVIRI is calibrated. The present study describes the radiative properties of these targets and evaluates the uncertainties associated with the characterization of this "reference", i.e. the modeled radiances. To this end, top-of-atmosphere simulated radiances are compared with several thousands of calibrated observations acquired by the European Remote Sensing 2/Along-Track Scanning Radiometer 2 (ERS2/ATSR-2), SeaStar/Sea-viewing Wide Field-of-view Sensor (SeaWiFS), Syste/spl grave/me Pour l'Observation de la Terre 4 (SPOT-4/VEGETATION), and the Environmental Research Satellite/Medium Resolution Imaging Spectrometer (ENVISAT/MERIS) instruments over the SEVIRI desert calibration sites. Results show that the mean relative bias between observation and simulation does not exceed 3% in the red and near-infrared spectral bands with respect to the first two instruments.     

Design of broadband microwave amplifiers with mixed-elements via reflectance data modeling

A practical method is introduced, to design single-stage broadband microwave amplifiers with mixed lumped and distributed elements via modeling the reflectance data obtained from lumped-element input and output matching network prototypes. The same transducer power gain level is obtained by using less number of lumped-elements in the mixed-element amplifier than that of the lumped-element amplifier prototype. A mixed-element amplifier design is presented, to exhibit the utilization of the method. It is expected that the method will be employed, to design microwave amplifiers for broadband communication systems.     

Radiative transfer modeling of cross-polarized backscatter from a pine forest using the discrete ordinate and eigenvalue method

Radiative transfer models have been widely used to interpret the radar backscatter from forested areas. Most of these models are based on an iterative solution of the radiative transfer equation, usually solved up to first or second order, thus taking into account single and double scattering. Although this method leads to results agreeing well with copolarized backscatter measurements, it produces less accurate estimates for horizontal-vertical (HV) polarization. This paper presents a radiative transfer backscatter model that accounts for multiple scattering by using the discrete ordinate and eigenvalue method applied to a layered medium. Using parameters derived from an architectural tree model, calculations at C- and L-band are compared with HV data acquired for a maritime pine forest in the southwest of France during the Spaceborne Imaging Radar-C missions. Good agreement is found at C-band for all values of forest biomass, and reasonable agreement at L-band for high biomass, when the soil backscatter plays a minor role. For low biomass, the L-band modeling is inadequate because of difficulties in estimating the soil backscatter. Comparison with calculations from a first-order radiative transfer model shows that multiple scattering is significant, especially at C-band.     

肌肉组织的光透射特性与辐射传输理论的修正

为了更确切地认识光在生物组织内的传输规律,通过实验测量研究了鸡肌肉组织和猪脂肪组织切片的光透射特性.结果表明,激光束经过肌肉组织后,能在远场处产生明显的衍射条纹.为了解释这种衍射现象,将衍射效应考虑进辐射传输模型,对辐射传输理论进行了修正.修正后的辐射传输理论不仅能定性地说明肌肉组织衍射现象的成因,而且其数值结果与实验现象吻合较好,说明了修正后辐射传输理论的正确性.