太阳天顶角对反演高光谱地表反射率影响分析

为了满足星上载荷高频次的在轨定标需求,常使用场地自动化定标技术将多光谱反射率反演为高光谱反射率,所以提升光谱的反演精度对提高自动化定标精度尤为重要。使用布设在敦煌辐射校正场的通道式自动化观测仪器计算从2018年9月至2019年9月的反射率;根据测量过程中太阳天顶角的不同将数据分为6组,并使用双向反射分布函数模型对不同太阳天顶角下的光谱形状进行一致性分析。实验结果表明,双向反射分布函数模型校正不同入射角度是有效的。     

不同融化状态雪的偏振特性分析

在当今全球变暖的形势下,传统对于固态雪的研究已无法满足需求,文章定性分析了不同融化状态雪的偏振反射光谱,重点探讨了偏振角、方位角、光线入射天顶角和探测天顶角与不同融雪类型的关系,发现这些因素对不同融雪类型的偏振反射光谱均有影响。在可见光波段,融雪在90°偏振时的反射比最大,0°偏振时最小;探测角与入射角越大时,融雪的偏振反射比也越大;不同方位角时的融雪偏振反射光谱出现异于其他地物光谱的反常现象;某些波段的偏振光谱特征对判断融雪含水量大小具有一定意义;同时随着含水量的增加偏振反射比显著下降。这些规律为以后利用偏振光谱定量分析融雪特性奠定了基础,同时在淡水资源管理和监测春汛等自然灾害方面也有一定的现实意义。     

冬小麦冠层光谱的方向性特征分析

二向性反射因入射和观测的角度变化而变化,合理选择遥感观测角度、太阳天顶角等为提高遥感应用精度提供可能。通过采用各向异性因子和各向异性指数定量分析了冬小麦冠层窄波段二向性反射率及NDVI的方向性特征。分析结果表明：主平面内二向性反射率的各向异性最强,垂直主平面最弱,其他平面介于前两者之间;可见光波段反射率随观测天顶角的敏感性大于近红外波段;反射率对太阳天顶角的敏感性随着观测天顶角的增大而增大。前向NDVI整体上大于后向,且NDVI随着太阳天顶角的增大呈增大趋势。为了减少观测方式所带来的不确定性,应尽量选择近红外波段和小太阳天顶角,估算结构参数时应尽量选择主平面进行遥感观测,在利用NDVI估算生物物理参数时尽量远离“热点”区域。     

基于粗糙样片光谱BRDF的空间目标可见光散射研究

实验测量了某种卫星包覆材料和太阳能电池板样片在可见光波段(400~780 nm)的光谱双向反射分布函数.将样片的光谱双向反射分布函数对可见光波段内的太阳谱辐射照度加权平均,获得了可见光入射时目标样片表面的平均双向反射分布函数,并利用遗传算法建立了其参量化统计模型.应用此模型,结合目标的几何建模、消隐,计算了可见光入射时某卫星散射光强度的空间分布,并分析了其与卫星的几何形状、表面材料等的关系.     

An effective reflectance method for designing broadband antireflection films coupled with solar cells

The solar spectrum covers a broad wavelength range,which requires that antireflection coating(ARC) is effective over a relatively wide wavelength range for more incident light coming into the cell.In this paper,we present two methods to measure the composite reflection of SiO2/ZnS double-layer ARC in the wavelength ranges of 300-870 nm(dualjunction) and 300-1850 nm(triple-junction),under the solar spectrum AM0.In order to give sufficient consideration to the ARC coupled with the window layer and the dispersion effect of the refractive index of each layer,we use multidimensional matrix data for reliable simulation.A comparison between the results obtained from the weighted-average reflectance(WAR) method commonly used and that from the effective-average reflectance(EAR) method introduced here shows that the optimized ARC through minimizing the effective-average reflectance is convenient and available.     

An effective reflectance method for designing broadband antireflection films coupled with solar cells

The solar spectrum covers a broad wavelength range, which requires that antireflection coating (ARC) is effective over a relatively wide wavelength range for more incident light coming into the cell. In this paper, we present two methods to measure the composite reflection of SiO₂/ZnS double-layer ARC in the wavelength ranges of 300-870 nm (dual-junction) and 300-1850 nm (triple-junction), under the solar spectrum AM0. In order to give sufficient consideration to the ARC coupled with the window layer and the dispersion effect of the refractive index of each layer, we use multi-dimensional matrix data for reliable simulation. A comparison between the results obtained from the weighted-average reflectance (WAR) method commonly used and that from the effective-average reflectance (EAR) method introduced here shows that the optimized ARC through minimizing the effective-average reflectance is convenient and available.     

陆基条件下典型地物和伪装光谱影响因子分析

近年来,随着军事侦察识别技术的快速发展,用于侦察探测的军事装备已经逐步实现高精度化水平,拥有高技术侦察手段的一方往往可以对目标实施精准打击,大大降低战争胜利的成本。在高光谱成像方面,目前比较成熟的有卫星遥感和高空航空成像技术,这两种成像方式侦察时间大致相同,入射光方向基本一致,并且由于高光谱设备基本垂直于地面,因而反射光方向保持不变, 地物的BRDF系数比较固定。在陆军应用时,侦察时间随机,太阳的入射角度时刻变化,而且侦察的方向任意,高光谱在地面或者近地位置,探测方向变化无穷,地物在不同成像条件下的光谱曲线受到物体表面的BRDF系数影响凸显。通过展开不同的实验,挑选了绿地植被和三种人造伪装材料,细致的分析了太阳高度角、方位角和探测角对陆基条件下地物光谱的影响。实验结果表明,虽然四种材料的反射特性存在差异,但在不同的太阳高度角、探测角以及探测器与地物的方位角上呈现相似的规律。对于太阳高度角,当探测角一定时,人造伪装物光谱一般随着太阳高度角的变化整条光谱曲线都发生变化,反射比曲线呈现出平移的规律,而绿地植被在白光波段变化不很明显,在近红外波段的变化很明显,随着太阳高度角的升高先升然后降低;对于方位角而言,四种材料随着方位角的增大,光谱反射比一般先升高后降低,同时后向观测时的反射比一般比前向观测时大;对于探测角,三种材料的光谱反射比与探测角的关系并不很大,但三种材料均在不同的探测角度上出现了“热点”现象。最后,对绿地植被和迷彩伪装板的BRDF模型参数进行了分析,得到了其在不同方向上的反射规律。     

星上定标漫射板远紫外BRDF测量方法

针对星载漫射板远紫外波段(140~240nm)的双向反射分布函数测量过程中,探测器响应线性问题和紫外光源稳定性差的问题,提出一种采用光源监测比例补偿的相对测量方法.根据测量方法设计了一种基于六自由度转台结构形式的测量系统,该系统采用漫射板两维平移+两维转动、探测器两维转动的组合运动形式,可实现漫射板半球空间内任意点、任意方位的双向反射分布函数测量.用所提方法进行测量实验,并对影响系统测量结果的主要因素进了不确定度分析,结果表明总测量不确定度约为5.5%.     

入射角对Al0.5Ga0.5As-AlAs分布布拉格反射器反射光谱的影响

采用传输矩阵法对Al0.5Ga0.5As-AlAs材料的发光二极管分布布拉格反射器进行入射角的反射光谱研究,计算发现反射偏振光p和s随入射角的增大呈“V”形变化,在49.8°处有最小反射值。不同入射介质[以空气和限制层(Al0.7Ga0.3)0.5In0.5P材料]下的反射光谱受入射角的影响差异很大,其中入射角对空气入射介质的反射谱影响较小,由0°入射的反射率88.13%降至45°的84.94%,反射峰值波长蓝移仅10 nm;但入射角对(Al0.7Ga0.3)0.5In0.5P入射介质的反射谱影响很大,仅从0°到45°入射,反射率降幅就超过45%,反射峰值波长蓝移超过127 nm。为了减缓这种影响,提出了多波长布拉格反射器结构设计。计算表明多波长分布布拉格反射器在0ο~45°的入射角内比传统的分布布拉格反射器有更好的光谱特性,这对提高发光二极管的出光效率有现实意义。     

多角度偏振高光谱的农田土壤肥力模型研究

随着精准农业这一理念的提出，快速精确获取农业信息成为人们关注的重点。偏振遥感因其结合了多角度遥感的特点，高光谱遥感和微波遥感的特点，从而能在不破坏地物的基础上提高探测和识别地物的准确度。以往的研究主要以单一土壤肥力指标为主。该实验通过实测吉林省典型地区农田土壤在不同状态下的光谱曲线，探讨了在确定最佳观测条件下的土壤肥力综合指标IFI与土壤光谱曲线的关系。结果表明光线探测天顶角、探测方位角、偏振状态均会在一定条件下影响土壤光谱曲线，但对光谱的形状和走向影响不大。在保证设备可达条件下，设计出遥感中监测土壤肥力的最佳方式。通过对光谱数据进行一阶微分和倒数的对数运算，在选定的特征波段上建立相应的肥力模型。结果表明土壤肥力与光谱反射比呈现明显的负相关关系，和光谱吸光度呈现明显的正相关关系，与光谱反射比的一阶微分相关关系不确定。在利用光谱反射比、光谱一阶反射比和吸光度特征参数进行土壤肥力估算时，发现光谱反射比与土壤肥力的二次函数拟合优度最佳，在560和860 nm处决定系数分别达到0.876和0.867。     

Antireflective properties of disordered Si SWSs with hydrophobic surface by thermally dewetted Pt nanomask patterns for Si-based solar cells

We have theoretically and experimentally investigated the antireflective properties of the disordered subwavelength structures (SWSs) with a hydrophobic surface on silicon (Si) substrates by an inductively coupled plasma (ICP) etching in SiCl₄/Ar plasma using thermally dewetted platinum (Pt) nanopatterns as etch masks for Si-based solar cells. The Pt thin films on the SiO₂/Si surface were properly changed into the optimized dot-like nanopatterns via the thermal dewetting by rapid thermal annealing process. The antireflection properties were definitely affected by the etched profile of SWSs which can be controlled by the conditions of etching process. For the tapered Si SWS with a high average height of 724 ± 78 nm, the reflectance was significantly reduced below 5% over a wide wavelength range of 350-1030 nm, leading to a relatively low solar weighted reflectance of 2.6%. The structure exhibited reflectances less than 14.8% at wide incident angles of 8-70°. The hydrophobic surface with a water contact angle of 113.2° was obtained. For Si SWSs, the antireflective properties were also analyzed by the rigorous coupled-wave analysis simulation. These calculated results showed similar behavior to the experimental results.     

High-efficiency guided-mode resonance filter

A high-efficiency guided-mode resonance reflection filter is reported. The device consists of a surface-relief photoresist grating and an underlying HfO (2) waveguide layer deposited on a fused-silica substrate. The spectral response measured with a dye-laser beam at normal incidence exhibited a peak reflectance of 98% at a wavelength of 860 nm with sideband reflectance below ~5% extending over the wavelength range provided by the dye (800-900 nm). At normal incidence the filter linewidth was 2.2 nm. High-efficiency double-peak resonances occurred at nonnormal incidence, with the spectral locations of the maxima vayring with the incidence angle. The filter response at various angles of incidence agreed well with the theoretically calculated reflectance curves.     

激光入射角度对薄膜热场分布影响的数值分析

在多层介质薄膜中，激光的入射方式是影响薄膜抗损伤能力的关键因素之一.提出了一种模拟锥角高斯光入射多层介质薄膜后电场和热场分布的方法.该方法能够分析薄膜中高斯光各个角谱分量叠加形成的电场分布，进而得到由于薄膜本征吸收产生的热量沉积以及薄膜内部的温度场分布.针对中心波长为4.3 μm的中红外高反膜进行了分析，给出了高反膜系的温升峰值随激光入射角度和偏振态的变化.结果表明：对于s偏振光，斜入射时膜系的最高温升峰值高于垂直入射峰值，而p光的结果则相反.此种模拟方法克服了原有方法对激光入射角度的限制，较好地反映出斜入射情况下激光偏振态对薄膜损伤的影响. 关键词： 多层介质薄膜 高斯光 热过程 数值分析     

Sol-gel preparation and characterization of nanoporous ZnO/SiO2 coatings with broadband antireflection properties

Nanoporous ZnO/SiO₂ bilayer coatings were prepared on the surface of glass substrates via sol-gel dip-coating process. The structural, morphological and optical properties of the coatings were characterized. The refractive indices of ZnO layer and SiO₂ layer are 1.34 and 1.21 at 550 nm, respectively. The transmittance and reflectance spectra of the coatings were investigated and the broadband antireflection performance of the bilayer structure was determined over the solar spectrum. The solar transmittances in the range of 300-1200 nm and 1200-2500 nm are increased by 6.5% and 6.2%, respectively. The improvement of transmittance is attributed to the destructive interference of light reflected from interfaces between the different refractive-index layers with an optimized thickness. Such antireflection coatings of ZnO/SiO₂ provide a promising route for solar energy applications.     

基于改进非线性劈窗算法的VIIRS中红外海面耀斑区反射率计算

传感器入瞳处接收到的中红外波段(3~5 μm)能量包含反射的太阳能量与地物自身的发射能量。通常该波段反射的太阳能量很弱,但在海面太阳耀斑区等特定情况下,被中红外通道探测到的反射太阳能量是比较可观的,且其对大气影响的敏感性较低,同时,对于搭载有在轨定标系统的卫星传感器,使用黑体定标后的中红外波段的在轨辐射性能相当稳定的。因此,考虑将中红外波段的海面耀斑区反射率作为用于反射太阳波段交叉定标的基准。基于这个想法,构建了改进的、适用于VIIRS(visible infrared imaging radiometer)中红外波段的非线性劈窗模型来计算南印度洋海面耀斑区中红外反射率。首先统计得到VIIRS M12和M13波段海面反射率的限定关系,然后使用非线性劈窗算法模拟计算海面反射率,模拟模型的不确定度为0.83%。在此基础上使用VIIRS的M12波段(中心波长为3.697 μm)太阳耀斑区数据计算选取的样本区的海面反射率。然后使用两种方法对反射率精度进行验证,精度分别为0.29%和0.23%,假设M12和M13波段海面反射率相等的反射率计算结果精度分别为2.48%和1.03%。该计算模型大大提高了精度,说明该模型用于VIIRS M12中红外波段计算海洋耀斑区反射率是有效可行的,其精度能够满足中红外波段海面反射率作为波段间定标基准的需求。     

On the variability of the transmission coefficient of the atmospheric optical window

Summary We use experimental data to show that the amplitudeA of the oscillations impressed upon upper atmospheric electrons by the electric field vectors of incident solar radiation increases with the solar energy wavelength λ over the visible spectrum. Calculations based upon experimental data show that the transmission coefficientT of the upper atmosphere for incident solar energy (say at intensityI ₀) also increases with λ over the visible spectrum, implying thatT increases withA over the latter range. Finally we show thatI ₀ ^1/2 λ² bears a positive linear relationship withT over the visible solar spectrum. The latter conclusion, which confirms theoretical results contained in a recent paper, is then used to show that the 100 000 year eccentricity cycle effectively causes a maximum change in the total solar energy reaching the lower atmosphere of approximately 4.5% which is enough to trigger an ice age.     

An estimate of the secondary-proton spectrum at small atmospheric depths

Summary We have calculated the energy spectrum of secondary protons produced in the atmosphere as a function of the atmospheric depth and zenith angles at a location with zero geomagnetic cut-off. In this calculation, we have included all relevant energy losses and production processes. It is shown that the protons produced from the target nuclei through recoil and evaporation processes dominate the spectrum below 350 MeV. These calculations have been carried out over an energy region from 20 MeV to 40 GeV and up to a depth of 40 g/cm² of the atmosphere over a latitude with zero geomagnetic cut-off for both the periods of minimum and maximum solar modulation.     

Measurement of the electric fluctuation spectrum of magnetohydrodynamic turbulence

Magnetohydrodynamic (MHD) turbulence in the solar wind is observed to show the spectral behavior of classical Kolmogorov fluid turbulence over an inertial subrange and departures from this at short wavelengths, where energy should be dissipated. Here we present the first measurements of the electric field fluctuation spectrum over the inertial and dissipative wave number ranges in a Beta > or approximately = 1 plasma. The k(-5/3) inertial subrange is observed and agrees strikingly with the magnetic fluctuation spectrum; the wave phase speed in this regime is shown to be consistent with the Alfvén speed. At smaller wavelengths krho(i) > or = 1 the electric spectrum is enhanced and is consistent with the expected dispersion relation of short-wavelength kinetic Alfvén waves. Kinetic Alfvén waves damp on the solar wind ions and electrons and may act to isotropize them. This effect may explain the fluidlike nature of the solar wind.     

Optimized Mueller polarimeter with liquid crystals

We demonstrate a Mueller polarimeter in which the polarization-state generator and analyzer are both composed of a linear polarizer and two liquid-crystal variable retarders. The polarimeter is designed to optimize the accuracy of the final results by minimization of the condition numbers of the modulation and analysis matrices. The polarimeter calibration, a difficult task by conventional procedures, is achieved easily by use of the eigenvalue method of Compain et al. [Appl. Opt. 38, 3490 (1999)]. The overall polarimeter performance is tested with a linear polarizer at various angles and a compensator at various retardations.     

The reflection and polarization properties of non-spherical aerosol particles

In this paper, we investigate the capability of multi-angle TOA reflectance and polarized reflectance for the retrieval of aerosol properties including aerosol mode (fine mode and coarse mode), aerosol shape (sphere and non-spherical), and aerosol optical thickness. Single-scattering parameters and phase-matrix elements were computed for randomly oriented non-spherical aerosol particles. Sensitivity indices were introduced to quantify the sensitivity of the TOA total reflectance and polarized reflectance to aerosol parameters. Finally, on the basis of the sensitivity study, this paper presents a conceptual approach toward the remote sensing of non-spherical aerosol three parameters (aerosol mode, aerosol shape, and aerosol optical thickness) using the TOA total reflectance and TOA polarized reflectance for the 0.865 μm spectral bands measured at multiple viewing angles.