海水中矿物质颗粒吸收和散射特性Mie理论分析   总被引：1，自引：0，他引：1  

周雯  曹文熙  李彩 《热带海洋学报》2008,27(1):22-26

利用Mie理论模型对不同粒径分布和复折射率的矿物质颗粒吸收和散射特性进行了模拟计算.颗粒的衰减和散射效率随着参数ρ的增大呈现出振幅依次减小的一系列有规则的振荡变化,而吸收效率则随着ρ的增加而增大;随着颗粒吸收性的增强,散射效率和吸收效率随着ρ的增大最终都将趋近极限值1.对于矿物质颗粒群,颗粒群的粒度分布变化对散射和后向散射特性影响很大,小粒径粒子对散射和后向散射的贡献比较大;折射率实部以及虚部变化对散射特性均有影响,颗粒的吸收性越强,则散射会相应地减弱;粒度分布以及折射率虚部对吸收系数也存在较大的影响,但是折射率实部对吸收系数的影响不大.  相似文献   

雷达图像模拟方法分析          下载免费PDF全文

张永贺  宋芳  王番  王冬红 《海洋测绘》2008,28(2):75-78

目前最常用的雷达图像模拟方法有两种：以信号为基础的模拟方法和以特征为基础的模拟方法。首先介绍了雷达图像模拟的重要性，然后分析了两种方法的原理和特点，给出了各自的模拟流程，最后根据某一场景的DEM数据实现了该场景雷达图像的模拟，讨论两种模拟方法的侧重点和应用范围。  相似文献   

Radar attenuation due to melting: a comparison of physical models proposed for the melting morphology     

S. D. Korkmaz 《Atmospheric Research》2004,70(3-4):261-274

The radio wave attenuation through the melting layer at various frequencies is investigated. The effect of the melting morphology on the attenuation computed by the Mie theory is discussed. To obtain the rate of melting of snowflakes, a melting model is given. In this model, the six different patterns proposed by Fabry and Szyrmer [J. Atmos. Sci., 56 (1999) 3593] to calculate the permittivity of the melting particles are used and the specific attenuation for each morphology is obtained. A comparison between the computed specific attenuation computed for the frequencies 2.8, 9.4 and 22.2 GHz is made. This analysis suggests that the large variability in the specific attenuation given by these models is due to the melting morphology in which the melting snow is modeled as a snow sphere surrounded by a water shell.  相似文献   

On the influence of wavelength-dependent light scattering on the UV-VIS absorption spectra of oxygen-based minerals: a study on silicate glass ceramics as model substances     

V. M. Khomenko  K. Langer  R. Wirth 《Physics and Chemistry of Minerals》2003,30(2):98-107

 The Mie scattering theory shows that the presence of randomly distributed submicroscopic inclusions with narrow size distribution and a refractive index n _i in a matrix with different refractive index n _m may give rise to a λ-dependent, band-like scattering (e.g., Kortüm 1969). Intensity and spectral position of this scattering depend on a combination of several independent parameters, such as size and number of inclusions, their form and n _i /n _m ratio (Kortüm 1969). Recently, it was confirmed that at a certain inclusion size and n _i /n _m ratio the scattering bands can contribute to the UV-edge in the electronic absorption spectra of garnets, influencing their colour (Khomenko et al. 2001). In natural minerals, however, it is impossible to differentiate between individual influence on scattering of the above mentioned parameters because of complex and interconnected variations in number, size and type of inclusions. Additionally, in most natural minerals variable amounts of transition metal ions are present. They may cause UV-VIS absorption due to ligand to metal charge transfer (LMCT) in the same region where band-like scattering may occur (Khomenko et al. 2001). At least some of these difficulties may be avoided in the case of some glass ceramics where number and size of crystalline microinclusions can be controlled by varying ceramization conditions such that fine-grained homogeneous microstructures are formed (e.g., James 1982; Petzoldt and Pannhorst 1991). Thus, glass ceramics of known composition, containing different amounts of microcrystals of specified size, may serve as unique patterns for the experimental study of effects caused by submicrocrystals on bulk properties of transparent solid materials, such as scattering, UV-VIS transparency and colour. Four types of parent glasses and a series of glass ceramic materials produced from them by heat treatment were investigated using transmission electron microscopy (TEM). These materials were also studied by transmission spectrometry in the range 35 000–20 000 cm⁻¹. Different inclusions, from five to several hundred nm in size, were observed in the glass matrices depending on their compositions and heating history. These inclusions represent two groups: early very small crystals of Ti, Zr oxides and relatively large crystals of stuffed high-quartz type or keatite. The absorption spectra of the glass ceramics show largely varying long-wavelength slopes of the UV absorption. UV-edge intensity correlates mostly with the size of the inclusions and changes drastically when larger keatite-type microcrystals are growing. Small variations in the UV edges also follow the early process of Ti-phase separation and nucleation. This may be explained by Ti depletion from the glass matrix and, thus, by reducing the measured intensity of LMCT in the first co-ordination sphere of Ti⁴⁺ ions. The different yellowish colourations of unheated glasses studied here are caused by this effect, whereas developing several hundred-nm-large keatite crystals leads to a strong scattering effect and a milky colour in glass ceramics. Received: 15 February 2002 / Accepted: 11 November 2002 Acknowledgements M. Garsche and A. Kisljuck generously provided the base glass and glass ceramic samples. F. Galbert and S. Herhing-Aghte, both at the Technical University Berlin, helped with electron microprobe analyses and refractive indices measurements, respectively. The Deutsche Forschungsgemeinschaft, Bonn-Bad Godesberg, provided financial support through grant La324/35. To all these individuals and this institution our sincere thanks are due.  相似文献   

海洋表面流的高频雷达遥感   总被引：9，自引：2，他引：9       下载免费PDF全文

侯杰昌  吴世才 《地球物理学报》1997,40(1):18-26

解释了利用高频雷达探测海洋表面流的基本原理，简要介绍了新研制的海态监测分析雷达OSMAR的组成及其工作流程，着重分析了利用OSMAR探测北部湾海流的实验结果．  相似文献   

Research on coda Q distribution in Beijing and its surrounding regions   总被引：2，自引：0，他引：2  

马云生  张天中  张焕生 《地震学报(英文版)》1995,(4)

ＲｅｓｅａｒｃｈｏｎｃｏｄａＱｄｉｓｔｒｉｂｕｔｉｏｎｉｎＢｅｉｊｉｎｇａｎｄｉｔｓｓｕｒｒｏｕｎｄｉｎｇｒｅｇｉｏｎｓＹｕｎ－ＳｈｅｎｇＭＡ（马云生），Ｔｉａｎ－ＺｈｏｎｇＺＨＡＮＧ（张天中）ａｎｄＨｕａｎ－ＳｈｅｎｇＺＨＡＮＧ（张焕生）（Ｉｎｓｔ...  相似文献   

Broad-bandwidth, sound scattering, and absorption from krill (Meganyctiphanes norvegica), mysids (Praunus flexuosus and Neomysis integer), and shrimp (Crangon crangon)     

Conti  Stephane G.; Demer  David A.; Brierley  Andrew S. 《ICES Journal of Marine Science》2005,62(5):956-965

  相似文献   

An innovative block partition and equivalence method of the wave scatter diagram for offshore structural fatigue assessment     

《Applied Ocean Research》2016

The fatigue assessment plays an increasing role for the offshore structural safety. Many fatigue assessment methods have been developed for this purpose. Among those methods, the time domain method is regarded as the most accurate method but less adopted in practice due to time consuming. In order to improve the efficiency of the time domain method, an innovative block partition and equivalence method of the wave scatter diagram is developed for offshore structural fatigue assessment. After the wave scatter diagram is partitioned into several blocks, the newly developed method, involves determination of the equivalent wave height, wave period and occurrence probability of the representative sea states based on modified energy equivalent principle. The equivalent wave period of the representative sea state is calculated via the spectral moment formula in which the equivalent spectral moments of zero and second order are obtained based on the weighted averaging principle. Combining with the determined wave period, the equivalent significant wave height can be determined by reversing the wave spectrum integral formula, where the equivalent wave energy of a divided block of the wave scatter diagram is modified by introducing a factor to compensate the effect of low- and high-amplitude cycles fatigue damage. The equivalent occurrence probability is equal to the summation of the original sea states’ occurrence probability within the divided block. The developed method has the advantage of preserving the stochastic characteristics of the short term sea states within the divided block during determining the representative sea state. At the same time the newly developed method has no limitation on block partition and can be applied on different offshore structure. Two structural models, a fixed mono-pile platform and a floating semi-submersible platform, are demonstrated in the numerical examples. Results indicate that the newly developed method is robust, computationally affordable, and accurate within engineering expectations.  相似文献   

2013年北京地区一次强对流冰雹天气过程分析     

李浚河  耿建军  刘璐  孙兆斌  吴剑坤  杜佳  张淅妍 《沙漠与绿洲气象(新疆气象)》2016,10(2):25-30

2013年6月11日08时至6月12日08时,北京地区出现了一次强对流天气过程,部分站点出现冰雹、短时强降水等灾害性天气。本文详细分析此次过程的大尺度天气环流背景、物理量场、北京S波段新一代天气雷达基本反射率因子、径向速度、一小时累积雨量等产品和海淀风廓线探测数据、5分钟加密自动站数据,得出如下结论：(1)本次过程主要是对流层中层温度槽落后于高度槽,系统斜压性较强,发展较好。(2)源于东部沿海的暖湿空气持续输送,为后续强对流天气提供了充沛的水汽和不稳定能量。(3)本站不稳定能量的积聚为对流性天气的形成发展提供了良好的触发维持条件。(4)怀柔汤河口降雹之前,多普勒天气雷达速度图上反映出明显的中气旋特征;反射率因子图存在钩状回波,相应的垂直剖面具有回波悬垂、三体散射等特征。(5)南风分量明显加大,有利于水汽的输送,中尺度切变线的存在有利于气流辐合,强回波稳定少动,产生短时强降水。  相似文献   

极区ELDI随太阳活动的变化特征—— EISCAT/ESR雷达观测          下载免费PDF全文

黄定娟  蔡红涛李飞  胡坤李影余尧  马淑英 《极地研究》2017,29(1):101-110

利用1999—2011年EISCAT(EISCAT Tromsø UHF)和ESR(EISCAT Svalbard Radar)雷达的场向电子密度观测数据, 对比分析了两处雷达观测到的极区E层占优电离层ELDI (E-Layer Dominated Ionosphere)事件在太阳活动高、低年的统计特征。地面雷达观测表明, 太阳活动水平对极区ELDI发生率的空间分布影响显著: 在太阳活动高年, ELDI在EISCAT雷达处(极光椭圆区纬度)的发生率高于ESR雷达处(极尖/极隙区纬度); 在低年则恰好相反。夏季似乎不利于ELDI的发生, 且在该季节的变化特征不受太阳活动水平及空间位置变化的影响。两部雷达在太阳活动高年观测到ELDI的季节变化规律分别与低年期间的结果相一致: 在冬季和早春, ELDI的发生率较高, 其他季节发生率较低, 夏季尤其低。在ELDI事件期间, 两处雷达观测到事件的持续时间和电离层E层厚度随太阳活动水平的变化表现出明显差异: 高年事件的持续时间总体上比低年短, 低年观测到ELDI的厚度要小于高年结果; 然而N_mE/N_mF₂比值及H_mE却没有表现出明显依赖。  相似文献