Acoustic remote sensing of the atmosphere

I.IntroductionBy"remotesensing*ismeantatechniquefordctectingand/ormeasuringthelocation,shapc,featuresandstatcsofanobjcctfarbcyondbyaspecifiedtool.Andby"acousticremotescnsingoftheatmosphcre'isthusmeantthctechniquefordetcctingthcstatesoftheatmos-phercandvariousphenomenainitbysoundwavcsasatoo1farbeyond.Itisintcrcstingtonotethattheword"sound'means"acousticwaves'whenuscdasanoun,andhasthemeaningof"toexamine"or"toprobe'whenusedasatransitiveverb.ThcreIYomonecanscethecloserc1ationshipbetwccn"acoustic…     

Computational atmospheric acoustics

I.lntroductionTheterm"ComputationalAtmosphericAcoustics"doesnotyetappearformallyinlitera-turestillnow,thoughthesimilarterminologiesinsomeclosefieldsareadoptedsuccessivelyforquitealongtime,suchasComputationalFluidMechanics,ComputationalAcoustics,Compu-tationalHydroacousticsetc.Anyway,theresearchworkscontributedtothisfieldaresteadilyontheincreaseintheseyears.Itseemsthattheeventualformationofthefield"ComputationalAtmosphericAcoustics"wouldbejustroundthecorner.Themostfundamentalprobleminatmo…     

Study of the influence of thin layer loading on the propagation of Lamb waves using perturbation method

I.IntroductionSincethepublicationoftheclassicalpaper"Onthewavesinanelasticplate"byH.Lambin1917l1l,theterm"LaInbwave"hasbeenusedtorefertoanelasticdisturbancepropagatinginasolidplatewithfreeboundaries.Lambwavesarewidelyusedintheapplicationsofthedefectinspectionofthinwa.lledmaterial[2'8].InrecelltyearsLambwaveshavebeenwide1yusedinthefabricationofsensors.LamInwavesensorsdetectthechangesofenvironmentbymeasuringthechangeofphasevelocityofLambwaves.IncomparisonwithbuIkwavesandSAW's,Lambwavsprovi…     

Acoustic streaming induced by ultrasonic quasi-lamb waves in a plate

1Introduction"Lambwave"referstotheelasticwavepropagatinginathinpIatewithfreeboundaries.Ithasbeenwidelyusedinthefieldsofnon-destructiveevaluations(NDE)andmicrosensing['1'1.Iftheplateisincontactwithloads,i.e.,theboundaryisnotbothfree,thewavecanbecalledas"Quasi-Lambwave"[3].Apromisingapplicationof"Quasi-Lambwave"orLamb-WaveSensors(LWS)reportedbyMoroneyetal.istopumpfluidandtransportparticlesinasmallscalesystem[4].Bytracingthemicro-particlessuspendedinthefluidandmeasuringthevelocityofthem,th…     

近红外光纤探头

提出了近红外光纤探头"视距"模型.通过Monte Carlo模拟和两种不同光学性质的双层模型实验,得到了100 μm探头"视距"的经验公式.提出了三层模型的"视距"定义,给出了"层分辨率"的概念,并通过大鼠大脑的试验得到验证.利用近红外光纤探头"视距",可以区分不同的脑组织,在深脑探测手术中进行导航.探头"视距"提出了一个近红外探头视距研究的普遍方法,对光纤探头的设计有重要意义.     

弹弓效应原理简析

文章用速度变换和矢量图对"弹弓效应"的加速原因做出了较为简洁直观的解释,以关于"弹弓效应"的一个简例.分析"弹弓效应"中的加速条件,得出能使入射物体被加速的偏转角范围.与通常所采用的两体碰撞理论相比较,此方法更能凸显"弹弓效应"的加速机理,且能有效避免冗繁的数学运算.将"弹弓效应"与粒子散射问题对照分析,得出两者之间的可类比性.因而可由散射问题中的散射角关于瞄准距离的公式类比推出"弹弓效应"中偏转角与瞄准距离之间的关系.文章还将"弹弓效应"的思想推广到了一般尺度上的两体问题.     

新课改中,农村初中物理实验教学存在的问题及对策

物理是以实验为基础的自然科学,所谓物理,就是通过"物"--物理实验引入物理概念,研究物理规律.就是要以"物"喻出"理"的本质,以"物"明了"理"的内涵,以"物"揭示"理"的真谛.因此,物理实验是学生获取知识、进行知识创新的重要手段,是培养学生的学习兴趣、科学态度和提高学生终身学习能力的重要途径.     

电磁学中的电路抽象

首先简要回顾"场"与"路"的基本内容,从基本体系上进行比较并列出二者物理量关系.然后从电磁学中电路抽象角度阐明"场"衍生"路"的建模方法及"第四类"基本无源元件演绎.最后,给出的应用实例——生物组织检测的共振光声光谱.     

Interchannel phase difference and stereo sound image localization

1IntroductionInstereophonicreproductionwithinterchannelphasedifference,theimagelocalizationtheorywasfirstpresentedbyY.Makita[1].Lettheanglebetweentwoloudspeakersbe2O(o=O"isinthefrontdirectionando=9O'totheleft),andthesignalsfedtotheloudspeakersarewhereL,Raretheamplitudesoftwosignalsrespectively,-l8O"o"isphaselag,andn相似文献   

建设以知识、能力和素质为教学目标的大学物理精品课程

介绍了同济大学基础物理教学在精品课程建设中的成功经验.为贯彻"以学生为本"的基本教学指导思想,教研室的老师们提出了"环境浸润"的教学理念,建立了物理探索实验室和物理教学辅助网.以课堂教学为主渠道,开展多种形式的教学活动,形成了"课内与课外结合"、"理论与实践结合"、"教学与育人结合"的教学模式.通过多年的教学实践,取得了良好的教学效果.学生对物理学产生了兴趣,涌现出了一批具有较高水平的学生论文和作品.学生的综合能力和素质得到了培养.     

基于压缩拷贝场向量的空域滤波器设计

近几十年来,匹配场处理技术得到了广泛深入的研究,并针对实际应用提出了一系列的具体处理算法.当感兴趣的水下目标信号被水面强干扰信号掩蔽时,对水下目标的匹配场处理定位性能显著下降.现有的广义空域滤波器可以抑制水面强干扰,但计算速度较慢并且内存消耗较大.提出了一种基于压缩拷贝场算法的空域滤波器设计方案,并通过非相干叠加处理宽带问题.相对于现有的空域滤波器,当接收阵元数N大于波导中有效简正波号数Q时,该滤波器可以大幅度缩减计算时间、节约运行内存,并且保持了对水面强干扰的抑制性能.针对近岸浅海环境进行了仿真计算,并给出了一些近岸浅海海域试验数据处理结果,验证了该空域滤波器的性能和对计算速度的提升.结果表明,应用基于压缩拷贝向量的矩阵滤波器对强干扰下的弱目标进行宽带非相干匹配场定位,可实现水下目标的有效区分.     

Null-broadening in a waveguide

Null-broadening, introduced in plane wave beamforming, is extended to an ocean waveguide in the context of matched field processing. The method is based on the minimum variance processor with white noise constraint and the distribution of fictitious sources using the theory of waveguide invariants. The proposed method is demonstrated in simulation as well as with data collected during the SWellEx-96 experiment. As another application, it is shown that the width of a null can be controlled in an adaptive time reversal mirror with a source-receive array.     

A Bayesian approach to matched field processing in uncertain ocean environments

An approach of Bayesian Matched Field Processing （MFP） was discussed in the uncertain ocean environment. In this approach, uncertainty knowledge is modeled and spatial and temporal data received by the array are fully used. Therefore, a mechanism for MFP is found, which well combines model-based and data-driven methods of uncertain field processing. By theoretical derivation, simulation analysis and the validation of the experimental array data at sea, we find that （1） the basic components of Bayesian matched field processors are the cor- responding sets of Bartlett matched field processor, MVDR （minimum variance distortionless response） matched field processor, etc.; （2） Bayesian MVDR/Bartlett MFP are the weighted sum of the MVDR/Bartlett MFP, where the weighted coefficients are the values of the a posteriori probability; （3） with the uncertain ocean environment, Bayesian MFP can more correctly locate the source than MVDR MFP or Bartlett MFP; （4） Bayesian MFP can better suppress sidelobes of the ambiguity surfaces.     

Matched-field replica model optimization and bottom property inversion in shallow water

Matched-field replica models based on an inaccurate knowledge of geoacoustic parameters such as bottom attenuation, shear, and interfacial sound-speed discontinuities, can predict an incorrect number of propagating modes for a shallow-water channel. The resulting degradation in the matched-field ambiguity surface can be substantially reduced by obtaining optimal replica models via modal-sum-limit optimization or bottom-property inversion. The use of these techniques for multi-tone (70, 95, 145, and 195 Hz) source-tow data recorded near San Diego during the first Shallow-Water Evaluation Cell Experiment (SWellEX-1) significantly increased matched-field correlation levels and improved source localization relative to results obtained with a previous nonoptimized model. The predicted number of propagating modes was also reduced substantially. The inversion for bottom properties (attenuation, interfacial sound-speed discontinuities, no shear) provided sediment attenuation estimates which agree well with Hamilton's models and were an order-of-magnitude greater than that used in the nonoptimized model, which accounts for the reduction in the number of modes. A simulated modal decomposition using the inverted optimal replica model verifies the number of modes predicted by the modal-sum-limit optimization.     

一种水平变化波导中匹配场定位的虚拟时反实现方法

在水平变化波导中,匹配场被动定位的计算量非常大,严重阻碍了其工程应用.本文提出了一种水平变化波导中匹配场定位的虚拟时反实现方法,其抛物方程模型计算网格总数远小于匹配场处理,从而大大减小计算代价.与匹配场处理不同,虚拟时反实现方法是一个利用介质互易性和叠加性的后向传输过程.通过在各水听器位置放置虚拟声源,并在搜索区域产生相应的模糊平面,对各个模糊平面进行相应加权求和,获得的定位模糊平面.利用地中海浅海实验数据验证了虚拟时反实现方法的快速性能.     

Medical ultrasound imaging method combining minimum variance beamforming and general coherence factor

In medical ultrasound imaging field,in order to obtain high resolution and correct the phase errors induced by the velocity in-homogeneity of the tissue,a high-resolution medical ultrasound imaging method combining minimum variance beamforming and general coherence factor was presented.First,the data from the elements is delayed for focusing;then the multi-channel data is used for minimum variance beamforming;at the same time,the data is transformed from array space to beam space to calculate the general coherence factor;in the end, the general coherence factor is used to weight the results of minimum variance beamforming. The medical images are gotten by the imaging system.Experiments based on point object and anechoic cyst object are used to verify the proposed method.The results show the proposed method in the aspects of resolution,contrast and robustness is better than minimum variance beamforming and conventional beamforming.     

The array invariant

A method is derived for instantaneous source-range estimation in a horizontally stratified ocean waveguide from passive beam-time intensity data obtained after conventional plane-wave beamforming of acoustic array measurements. The method has advantages over existing source localization methods, such as matched field processing or the waveguide invariant. First, no knowledge of the environment is required except that the received field should not be dominated by purely waterborne propagation. Second, range can be estimated in real time with little computational effort beyond plane-wave beamforming. Third, array gain is fully exploited. The method is applied to data from the Main Acoustic Clutter Experiment of 2003 for source ranges between 1 to 8 km, where it is shown that simple, accurate, and computationally efficient source range estimates can be made.     

利用宽带引导声源重构拷贝声场的目标声源定位

为了避开传统的匹配场目标定位技术对环境先验知识的依赖性,提出了在均匀浅海环境中只知道少量环境参数的情况下,利用垂直接收阵和不同距离上的两枚宽带引导声源重构声场对目标声源进行定位的一种方法。这种方法主要基于简正波估计和声场重构两种关键技术,同时省去了匹配场定位技术中大量的拷贝声场计算。数值仿真主要采用线性Bartlett匹配处理器分析了目标定位效果,在信噪比高于10 d B的情况下,定位效果良好。     

Ocean bottom profiling with ambient noise: a model for the passive fathometer

A model is presented for the complete passive fathometer response to ocean surface noise, interfering discrete noise sources, and locally uncorrelated noise in an ideal waveguide. The leading order term of the ocean surface noise contribution produces the cross-correlation of vertical multipaths and yields the depth of sub-bottom reflectors. Discrete noise incident on the array via multipaths give multiple peaks in the fathometer response. These peaks may obscure the sub-bottom reflections but can be attenuated with use of minimum variance distortionless response (MVDR) steering vectors. The seabed critical angle introduces discontinuities in the spatial distribution of distant surface noise and may introduce spurious peaks in the passive fathometer response. These peaks can be attenuated by beamforming within a bandwidth limited by the array geometry and critical angle.     

利用拖船辐射噪声的深海声学参数近场匹配场反演方法

针对深海声学参数难以通过远距离合作声源反演获取的问题,提出了利用拖船低频噪声近场匹配场反演方法。首先,利用聚焦波束形成计算拖曳阵接收拖船噪声的方向性,获得传播路径特征;然后,构建多参数反演模型,由波数积分声传播模型计算拷贝场,采用遗传算法对多频匹配场目标函数进行反演。同时,采用蒙特卡罗方法分析参数后验概率密度。仿真与试验结果表明:深海环境中拖曳阵接收拖船噪声主要来自海底反射路径,利用该特性反演得到海水深度、噪声源距离、阵列深度、沉积层厚度等参数,多频联合反演可以提高沉积层厚度等参数反演准确性。宽带匹配场处理表明,利用反演最优参数模型能准确给出拖船噪声源的空间位置。