共查询到20条相似文献,搜索用时 0 毫秒
1.
Zhongqiu Sun Yunsheng Zhao 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(14):2372-2383
The linear polarization of light reflected from snow surfaces was measured by an instrument composed of a semi-automatic goniometer and an ASD spectroradiometer under a direct lamp to determine its potential to detect differences in grain size. The Stokes parameters were computed for all snow samples. The results confirmed that the degree of polarization increased in bright bands and decreased in dark bands with an increase in grain size. The trend was more obvious in the near-infrared bands and in the forward direction. As the snow grain size varied the contribution of Q parameter to the degree of polarization was more than the U parameter, which was slight. Our results confirmed that the degree of polarization may be useful to distinguish the snow grain size. All above measurements were carried out in the laboratory where the atmospheric contribution was ignored. 相似文献
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Jouni Peltoniemi Teemu Hakala Juha Suomalainen Eetu Puttonen 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(17):1940-1953
The bidirectional reflectance factor and degree of linear polarisation of selected snow, soil, and gravel types have been measured using Finnish geodetic institute field goniospectropolariphotometer (FIGIFIGO). It was observed that with all measured samples the degree of linear polarisation is weakest 0–30 backwards from nadir, turning 1–5% negative in the backward direction, and growing larger (5–50%) in the forward and Brewster directions. Polarisation was found to be inversely but non-linearly proportional to reflectance. In addition, a wavelength-dependent trend was found to exist in some data, but in general, the wavelength dependence was smooth. Dry old snow polarises clearly more than melting snow or new snow. White gravel polarises somewhat similarly to snow in visible region, and black gravel resembles snow in infrared.The authors conclude that polarisation observations may be useful in land surface remote sensing, but that only far-forward angles (60–70) contain a strong enough signal for easy interpretation. The polarisation spectrum brings little additional information to reflection spectrum, but in conditions where the reflectance spectrum cannot be accurately normalised or incident irradiation is not known, polarisation spectrum could still be usable. The directional signal is strong and may yield refractive index or microstructure, and must be understood in any application. Polarisation near nadir is low for all known samples, and can thus be safely ignored with most non-polarised imaging applications. However, for accurate atmospheric polarimetry, e.g. by polarisation and directionality of the earth's reflectances (POLDER) or aerosol polarimetry sensor (APS) sensors, it is recommended to take into account land surface polarisation. 相似文献
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V. T. Prokopenko S. A. Alekseev N. V. Matveev I. V. Popov 《Optics and Spectroscopy》2013,114(6):961-964
The dependences of the polarization parameters of probe radiation on the observation geometry and relations between the Stokes vector parameters have been simulated based on the bidirectional reflectance distribution function as applied to active polarimetric systems. 相似文献
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Nuclear magnetic resonance water proton relaxometry is widely used to investigate pore size distributions and pore connectivity
in brine-saturated porous rocks and construction materials. In this paper we show that, by replacing water with acetone, a
similar method can be used to probe the porous structure of freeze-dried starch gels and therefore the ice crystal size distribution
in frozen starch gels. The method relies on the observation that the starch surface acts as a powerful relaxation sink for
acetone proton transverse magnetization so that Brownstein-Tarr theory can be used to extract the pore size distribution from
the relaxation data. In addition the relaxation time distribution is found to depend on the spectrometer frequency and the
Carr-Purcell-Meiboom-Gill pulse spacing, consistent with the existence of large susceptibility-induced field gradients within
the pores. The potential of this approach for noninvasively measuring ice crystal size distributions during freezing and pore
size distributions during freeze-drying in other food systems is discussed. 相似文献
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A. M. Timofeev 《Thermophysics and Aeromechanics》2018,25(5):765-772
Numerical simulation of thermal state was performed for semitransparent medium; the thermal state is formed under impact of incident radiation and convective heat transfer to the ambient medium. The model takes into account the heat transfer to the semi-infinite opaque substrate below the layer of semitransparent material. Computation was performed for governing parameters typical of snow and ice coating during winter period. Solving the radiative part of problem uses the modified average flux method. This method takes into account the dependence of optical properties on the wavelength of incident radiation, scattering, and reflective properties of the layer boundaries. 相似文献
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Based on the three-component assumption that the reflection is divided into specular reflection,directional diffuse reflection,and ideal diffuse reflection,a bidirectional reflectance distribution function(BRDF) model of metallic materials is presented.Compared with the two-component assumption that the reflection is composed of specular reflection and diffuse reflection,the three-component assumption divides the diffuse reflection into directional diffuse and ideal diffuse reflection.This model effectively resolves the problem that constant diffuse reflection leads to considerable error for metallic materials.Simulation and measurement results validate that this three-component BRDF model can improve the modeling accuracy significantly and describe the reflection properties in the hemisphere space precisely for the metallic materials. 相似文献
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《Waves in Random and Complex Media》2013,23(3):332-343
Through in-depth analysis of the scattering properties of a one-dimensional random rough surface, a method to calculate the spatial bidirectional reflectance distribution function (BRDF) characteristics of a randomly rough surface is proposed. The scattering characteristics of an electrically large rough surface can be substituted by combination of subsection electromagnetic fields. The radar cross-section (RCS), which is transformed from the BRDF, is compared with numerical results from the Method of Moment (MoM). The agreement of the results verifies that this method could calculate the electromagnetic scattering field efficiently and straightforwardly. Moreover, the resulting combined fields from the BRDF of subsections in the rough surface show a good match with the entire scattering field of a whole surface, which indicates that a large electrically rough surface could be feasibly and effectively substituted with the combination of scattering elements using the BRDF method and the statistical method. 相似文献
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导航系统中广泛采用激光测距确定星地间距离,双向反射分布函数可精确描述实际物体反射光的情况,是研究激光测距方程的有效手段。结合目标反射几何模型,计算得到透镜各点接收目标反射光强的表达式。对目标光斑和接收透镜进行网格划分,仿真得到透镜面元接收目标反射的光强分布和透镜接收的瞬时光强,并讨论了平面目标的网格步长选取和计算次数。当光束从不同空间位置入射至平面目标表面时,根据探测器-反射棱镜之间距离与接收光强的对应关系得到激光测距方程的待定参数。实测数据验证了理论计算的正确性。 相似文献
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This paper proposes a practical measurement system for bidirectional reflectance distribution functions (BRDFs) of a three-dimensional
(3D) object with a linear light source. Using the linear light source, the proposed system can reduce the number of image
acquisitions which are necessary for an estimation of the spatially-varying BRDFs of the object. Furthermore, the size of
the proposed system is much smaller than a conventional system which uses a parallel light. In this proposed system, the light
field of the linear light source is previously measured to determine direction and radiance of incident rays to each point
of the object, because the direction and radiance are not constant at each point. Using the proposed system, the BRDF of a
point of flat objects was experimentally measured, and results showed validation of the estimation accuracy of the proposed
system. Measurement efficiency of the proposed system was also evaluated by comparing reflectance model parameters estimated
by the conventional and proposed systems. For the estimation, the reflectance function of a 3D object was measured by both
systems. The estimation accuracy of the proposed method was also evaluated by comparing among a real image and rendered 3D
objects of the conventional and proposed methods. 相似文献
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Ram M. Narayanan Sandy R. Jackson 《International Journal of Infrared and Millimeter Waves》1997,18(5):959-990
Knowledge of surficial snow properties such as grain size, surface roughness, and free-water content provides clues to the
metamorphic state of snow on the ground, which in turn yields information on weathering processes and climatic activity. Remote
sensing techniques using combined concurrent measurements of near-infrared passive reflectance and millimeter-wave radar backscatter
show promise in estimating the above snow parameters. Near-infrared reflectance is strongly dependent on snow grain size and
free-water content, while millimeter-wave backscatter is primarily dependent on free-water content and, to some extent, on
the surface roughness. A neural-network based inversion algorithm has been developed that optimally combines near-infrared
and millimeter-wave measurements for accurate estimation of the relevant snow properties. The algorithm uses reflectances
at wavelengths of 1160 nm, 1260 nm and 1360 nm, as well as co-polarized and cross-polarized backscatter at a frequency of
95 GHz. The inversion algorithm has been tested using simulated data, and is seen to perform well under noise-free conditions.
Under noise-added conditions, a signal-to-noise ratio of 32 dB or greater ensures acceptable errors in snow parameter estimation. 相似文献
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The equilibrium shape of pure nickel and the effect of carbon on changes in the equilibrium shape at 1200°C were investigated. A statistical observation on the size-dependent, time-dependent and carbon-induced morphological evolution of crystallites suggested that the equilibrium crystal shape (ECS) of pure nickel is a polyhedron consisting of {111}, {100}, {110} and {210} surfaces. However, crystals with an extensive proportion of {320} surfaces were also frequently observed. The appearance of {320} surfaces was interpreted as kinetically stabilized metastable surfaces, which survived during the thermal equilibrating process, possibly due to a high nucleation energy barrier for their removal. On the other hand, the ECS of pure nickel was observed to change dramatically into a spherical shape with facets of {111}, {100}, {110} and {210} without exception under a carburized atmosphere, which indicates that carbon not only facilitates surface diffusion by which energetically more stable surfaces can be easily developed but also decreases the surface energy anisotropy. Together with X-ray photoelectron spectroscopy studies, it was proposed that the carbon-induced changes in the ECS are possibly due to a solid solution effect, which could lead to a reduction in the binding energy among atoms in the bulk as well as on the surfaces. 相似文献
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针对蓝相液晶显示器中的暗态漏光特性, 采用时域有限差分方法模拟计算了胆甾相液晶的平面态和焦锥态以及蓝相II态液晶的透射和反射特性, 得到了它们在正交和平行偏振片之间的漏光, 并提出了计算等效旋光能力的公式以比较它们的旋光能力. 通过对比焦锥态和蓝相液晶的旋光能力和漏光特性发现, 采用焦锥态替代蓝相液晶而得到良好的暗态特性是一种可行的方法. 通过研究它们的布拉格反射特性, 得知蓝相液晶的布拉格反射与平面态相似, 但反射强度小, 焦锥态无明显的布拉格反射特性. 相似文献
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The omnidirectional reflection properties in one dimensional superconductor-dielectric photonic crystal have been studied theoretically. In this present communication, the superconductor-dielectric photonic crystal in one dimension having alternate regions of superconductor-dielectric. The reflectance behaviors from these periodic multilayered structures are calculated for different angles of incidence. The reflectance and band structure is obtained by solving a Maxwell's equation using a translational matrix method. The study of reflectance bands of such superconductor-dielectric photonic crystal show that it can be used as broad band reflector. 相似文献
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本文在国产六面顶压机上,在5.6 GPa, 1250—1450℃的高压高温条件下,分别选用边长0.8, 1.5和2.2 mm三种尺寸的籽晶,系统开展了Ib型宝石级金刚石单晶的生长研究.文中系统考察了籽晶尺寸对宝石级金刚石单晶生长的影响.首先,考察了籽晶尺寸变化对宝石级金刚石单晶裂晶问题带来的影响.研究得到了籽晶尺寸变大,裂晶出现概率增加的晶体生长规律.其次,在25 h的生长时间内,考察了上述三种尺寸籽晶生长金刚石单晶时,生长时间与单晶极限生长速度的关系.得到了选用大尺寸籽晶,可以提高优质单晶合成效率、降低合成成本的研究结论.借助扫描电子显微镜和光学显微镜,对三种尺寸籽晶生长金刚石单晶的表面形貌进行了标定.最后,傅里叶微区红外测试,对三种尺寸籽晶生长宝石级金刚石单晶的N杂质含量进行了表征.研究得到了选用大尺寸籽晶实现快速生长金刚石的同时,晶体的N杂质含量会随之升高的晶体生长规律. 相似文献