基于高光谱数据提取水体叶绿素a浓度的混合光谱模型

从模型的精度和稳定性方面,与传统的经验模型比较显示,利用原始数据的一阶微分数据进行叶绿素a浓度混合光谱模型反演最佳。最后,以此模型对三种不同年份测量的地面高光谱数据进行了叶绿素a浓度的提取。实验结果表明混合光谱模型可以作为遥感监测水体叶绿素a含量的定量模型。     

Dynamic response analysis of nonlinear secondary oscillators to idealised seismic pulses

The paper deals with the seismic response analysis of nonlinear secondary oscillators. Bilinear, sliding and rocking single-degree-of-freedom dynamic systems are analysed as representative of a wide spectrum of secondary structures and nonstructural components. In the first stage, the equations governing their full dynamic interaction with linear multi-degree-of-freedom primary structures are formulated, and then conveniently simplified using primary-secondary two-degree-of-freedom systems and dimensionless coefficients. In the second stage, the cascade approximation is applied, whereby the feedback action of the secondary oscillator on the primary structure is neglected. Owing to the piecewise linearity of the secondary systems being considered, efficient semi-analytical and step-by-step numerical solutions are presented. The semi-analytical solutions allow the direct evaluation of the seismic response under pulse-type ground excitations and are also used to validate step-by-step numerical schemes, which in turn can be used for general-type seismic excitations. In the third stage, a set of decoupling criteria are proposed for the pulse-type base excitations, identifying the conditions under which a cascade analysis is admissible from an engineering standpoint. Finally, the influence and relative dependencies between the input parameters of the ground motion and the primary-secondary assembly are quantified on the response of the secondary systems through nonlinear floor response spectra, and general trends are identified and discussed.     

Bble Size Distribution for Waves Propagating over A Submerged Breakwater

Experiments are carried out to study the characteristics of active bubbles entrained by breaking waves as these propagate over an abruptly topographical change or a submerged breakwater. Underwater sounds generated by the entrained air bubbles are detected by a hydrophone connected to a charge amplifier and a data acquisition system. The size distribution of the bubbles is then determined inversely from the received sound frequencies. The sound signals are converted from time domain to time-frequency domain by applying Gabor transform. The number of bubbles with different sizes are counted from the signal peaks in the time-frequency domain. The characteristics of the bubbles are in terms of bubble size spectra, which account for the variation in bubble probability density related to the bubble radius r. The experimental data demonstrate that the bubble probability density function shows a-2.39 power-law scaling with radius for r＞0.8 mm, and a-1.11 power law for r＜0.8 mm.     

超随机特性对地震动谱特性和时间历程的影响

本文从单个地震动样本的角度分析了超随机部分对地震动波形的影响,认为自相关函数噪声部分或功率谱的随机波动部分对地震动波形的影响不大,对地震动的波形起主要控制作用的是地震动的相位谱或相位差谱,而自相关函数的噪声部分（或功率谱的随机波动成分）只对地震动波形起一定程度的调整作用。文中基于平稳随机过程的理论,用蒙特卡罗方法分析了自相关函数噪声项对人工合成地震动振幅和反应谱的影响：由于自相关函数的随机噪声项对地震动总功率或平方和的贡献为零,因此随机噪声项对合成地震动幅值的影响不大,但是由于自相关函数随机噪声项明显改变了地震动功率谱的形状和分布特征,使其出现了明显的波动,也在一定程度上提高了平均反应谱的峰值,从而对平均反应谱也产生一些影响。考虑地震动自相关函数中的随机噪声部分有助于更真实地模拟和反映地震动的真实特性。     

Semi-empirical estimation of ground motion using observed records at a site in Shikoku, Japan

A semi-empirical approach using fore- or after-shockrecords as Green's functions is applicable to thesimulation of strong ground motion, however suchrecords are obviously not available for predictionpurposes. Thus we have predicted ground motion fora hypothetical large earthquake from other minorevents by adopting a distance correction based ongeometrical spreading. Another difficulty inprediction is fault modeling. Surface traces weresimplified as fault models 27, 46, 55, and 77 km inlength. Further, the actual fault rupture may beinhomogeneous, so an asperity distribution isassumed. This asperity model assumes thatdislocation and stress drop are double than theaverage values. Although, the near field term isneglected in our simulation, no significantdifference was seen in the motions estimated byindividual models for periods up to 2.0 seconds. This indicates that the dependence of source size issmall for strong motion, perhaps as a result of therandom summation of high-frequency phases.     

热带沿海近地层大气的湍流结构和谱特征

利用１９９０年在海南省海口市天尾村的一次观测的资料，分析了速度分量谱、湍流强度等湍流特征量。这批资料多是有云影响情况下，稳定度参数（Ｌ）与热通量（ｗｔ）没有日变化规律，但湍能、平均温度仍具有日变化规律；湍谱的基本特征与晴天天气的谱基本相似，在惯性副区接近局地各向同性，速度谱符合相似理论的“－２／３”次方规律；根据Ｍ－Ｏ相似理论，探讨了各分量湍强δｉ／Ｕ＊（ｉ＝ｕ，ｖ，ｗ）与稳定度Ｚ／Ｌ的关系，表明各分量湍强与稳定度Ｚ／Ｌ仍具有“１／３”次方规律，但湍强和湍流能量比一般平坦地形下垫面的大     

Estimation of wave directional spreading in shallow water

This paper describes wave directional spreading in shallow water. Waves were measured for a period of 2 months using the Datawell directional waverider buoy at 15 m water depth on the east coast of India in the Bay of Bengal. The study also showed that in shallow water wave directional spreading was narrowest at peak frequency and widened towards lower and higher frequencies. The wind direction was found to deviate from the wave direction during most of the time. The unidirectional spectrum was found to be satisfactorily represented by Scott spectra.     

基于热红外遥感数据的西藏冈底斯东段岩性识别

ASTER数据包含有从太空测量来自地球表面的多光谱热红外辐射数据。通过对JHU光谱库中岩石矿物热红外光谱特征的分析,以及对ASTER影像TIR波段光谱特征进行分析,利用比值法和光谱角制图法SAM相结合进行石英、砂岩和硅酸盐岩类等造岩矿物识别并在西藏冈底斯东段泽当矿田应用,最后将遥感解译分析结果与该区已的地质资料进行比较。结果表明,ASTER影像TIR波段基本上能识别硅酸盐类造岩矿物,并且对于岩性识别具有很大的应用潜力。     

水面之上法测量水体光谱的关键技术

对水体光谱特征的研究是海洋水色遥感的基础工作之一。水体的光谱特征包括:表观光学特性和固有光学特性。在水体的表观光学特性研究方面,目前国际水色界推行的有:剖面法和水面之上法(也称表面法)。由于我国近岸水体混浊度较高,浅水区域较多,研究这类水体的表观光学特性应以水面之上法为主、剖面法为辅。介绍了水面之上法水体光谱的测量技术,就其中关键技术问题进行了讨论。