浅海沉积层中界面波的传播以及掩埋目标的回波

根据地声界面波的相关理论,采用时域有限差分法建立浅海沉积层中界面波传播模型。以沉积层中掩埋小目标为例,计算界面波对空腔掩埋物和实心掩埋物的不同作用结果。根据运动方程和应力应变关系采用中心差分网格建立声场的有限差分模型,计算了声场瞬态情况和质点振动的时间序列结果,从不同角度比较分析了地声界面波对掩埋目标的作用。根据浅海沉积层的性质计算了界面波的传播损失和对掩埋物体的目标强度,由于界面波传播衰减主要由沉积层的能量耗散引起,其规律接近横波的传播衰减,在高频情况下界面波在沉积层中传播的距离不远。文章试图建立一种对浅海沉积层中掩埋小尺度目标的探测新方法。通过一些典型模型的分析,从理论角度证明地声界面波对目标探测的可行性。     

半空间内二维圆柱声散射理论解析解

采用理论解析方法研究半空间内二维非紧致圆柱的声散射。齐次Helmholtz方程的解在柱坐标系内用自由空间格林函数的级数展开式表示。基于镜像源方法,利用刚性半空间边界反射圆柱散射声波来解决半空间边界和圆柱之间的多重散射。结合等效源原理,处理半空间边界质量型阻抗特性和刚度型阻抗特性对声传播的影响,推导单位强度简谐单极子点声源产生声场的理论表达式。总声场可以表示为四个分量的总和:入射声场、反射波以及圆柱和镜像圆柱的散射声场。采用边界积分方法对声散射进行计算,以验证理论公式的正确性。点声源模型的理论解析值与边界积分方法数值解在研究的波数和观察点角度范围内一致。     

球形障板对矢量水听器接收性能的影响

矢量水听器可以同步共点测量声场空间一点处的声压和质点振速的各个分量,因此其被广泛应用于水声测量、探测、通信等领域。矢量水听器在水声测量的应用中会受到安装载体散射声场的影响,而这种载体可以看作为障板,由于障板的存在使散射声场的分布发生改变,以及矢量水听器的接收性能下降。仅以绝对硬边界为例,对球形障板的散射声场进行了理论计算和仿真分析。并且对带障板条件下矢量水听器的接收指向性的变化进行了仿真研究。结果显示,从散射声场分布图可以直观看出声场发生的变化,矢量水听器的接收性能变化与障板的尺寸、与障板距离远近、声波发射频率等因素有关。     

一种物体前向散射声场异常的增强方法

0引言当物体穿过双基地声纳收发连线时,散射信号与直达信号时频空域上均发生重叠,此时双基地声纳传统的检测方法失效。但是,由于物体的前向散射作用,散射信号与直达信号产生干涉,使得接收声场会产生异常变化,该现象可作为物体入侵的标识。前向散射探测面临的问题是,随着接收距离的增大,直达波的干扰变强,前向散射引起接收声场     

薄壳目标的多基地声散射特性研究

文章对水中薄壳目标的多基地声散射特性进行了理论仿真与试验测量研究。首先采用有限元耦合边界元和基尔霍夫(Kirchhoff)近似积分两种不同的数值计算方法对内部充气球冠圆柱壳的多基地声散射特性进行建模仿真,然后通过目标在消声水池的散射声场试验测量验证仿真结果的有效性。采用相同的数值计算方法对Benchmark模型的多基地散射声场进行仿真计算,分析多基地(全向)声散射特性及散射机理。结果表明,水中目标多基地散射的回波强度与回波结构与多基地分置角相关,且回波亮点的主瓣宽度也随多基地分置角变化而变化;Benchmark模型的艇体和指挥舱之间存在强烈的干涉作用,使多基地(全向)散射声场的竖状条纹发生倾斜。研究为水下目标的多基地探测提供理论支持。     

复射线法及其在水声技术中的应用研究

声波是水中携带信息的最佳载体,水声技术是开展水下通信、探测等常用技术,具有较大的发展潜力。复射线法认为一个复源点的射线束,复源点与等效复源点关系和几何光学源点、等效光源关系是一致的,遵守几何光学ABCD定律,基于此学术界开展了大量基础研究。当前比较成熟的复射线法方法主要包括复射线法追踪法、复射线法近轴近似法、复合复射线法、复射线展开法等,在水声理论中复射线法技术主要用于指向性声场、计算散射场分析。近年来,有关于复射线法研究较少,特别是随着高速水声正交多载波调制(OFDM)通信系统的构建,反射法的应用领域变得十分狭窄,应将复射线法与非相干水声通信、相干水声通信、扩频水声通信相结合,以提高水声波的空间分辨率、提高波束形成算法的稳健性、提高波束形成的抗干扰能力。     

大粗糙度起伏下一维海面声散射建模与分析

针对起伏海面高频声散射计算问题,提出了一种改进的基尔霍夫(Kirchhoff)近似方法。该方法考虑了海面的阴影区和亮区之间的多次散射声场,可对小入射角下大粗糙度起伏海面的散射声场进行计算。以一维余弦和高斯谱海面散射声场的有限元计算结果为标准解验证了所提方法的准确性和适用性。利用该方法计算了一维余弦海面的散射强度,分析了不同入射声波频率和角度下海面散射强度的分布情况,并解释了Bragg散射的产生机理,同时讨论了不同海面均方根高度和相关长度情况下高斯谱海面散射强度的变化规律。     

浅海单模入射声场目标回波特性研究

浅海环境中,目标回波受到入射和散射双向过程的信道多途影响,具有复杂的多途结构。基于相控垂直阵的单模发射技术能激发出指定的单个简正波声场,可以降低海底混响干扰,简化目标回波多途结构,为主动探测提供了一种有效手段。在信道中点声源目标回波模型基础上,采用简正波本征函数加权研究了单模声场入射下球形目标散射问题,建立了浅海单模入射声场目标回波预报模型,并利用模型对刚性球回波进行了数值计算。结果表明:总声源级相同条件下,单模发射声场与传统的点声源发射声场相比具有一定的阵发射增益,目标回波具有较高的声压级;单模入射能够消除单程多途的影响,回波结构相对简单,有利于目标的探测和识别。     

水下刚性角反射器散射特性

为了分析水下角反射器的声散射特性,提出了一种计算水下凹面目标散射声场的方法。采用ANSYS软件构建水下角反射器实体模型,再利用声学分析软件SYSNOISE对其远场散射声场进行仿真。计算了二面角反射器的目标强度,并与声束弹跳法和板块元法的计算结果进行对比,验证了该方法的适用性和精确性。对三面角反射器的散射特性进行了分析,得到了不同声波入射角度下的目标强度、目标强度随频率的变化规律以及散射方向图,结果表明,正方形角反射器的目标强度最大,三角形角反射器的散射宽度最大,角反射器目标强度不存在明显的频率效应。计算了八面角反射体的方向图,计算结果表明角反射器组合可以有效增大目标强度和散射宽度。     

声波除灰技术中的物理声学问题

1　引　言　　声波除灰是指利用声场能量 ,清除和减缓锅炉换热器表面的积灰和结焦。声波除灰除包括系统的设计、生产、安装、调度与使用等一整套软、硬件技术外 ,炉内声场分布 ,特别是换热器表面声强大小应该是声波除灰技术能否实现除灰目的的重要因素之一。本文采用物理声学方法 ,计算了有限管数管排表面的多极子散射声场 ,讨论了壁面声强与声波频率、管数和管距之间的对应关系 ,找出了管壁表面声强值的峰值特性。对声波除灰技术的工业应具有指导意义。图 1　管排几何图2　基本方程　　设有Ｎ个半径为ａ的相同圆管 ,沿 ｙ轴等间距(管距为ｄ…     

Null detection of ballistic photons for locating objects buried in turbid media

We describe an optical system in which a vibration induced to a laser probe beam combined with a half-blocked photodiode allows determination of the position and width of objects buried in turbid media. Our system is based on the detection of an AC signal which drastically decreases under the presence of an obstructing buried object. We describe the technique and include experimental results showing that the system is capable of detecting 2?mm wide objects buried at depths up to 3?cm from the front surface of a sample simulating scattering properties of soft tissue.     

微弱激光辐射探测技术在激光告警设备中的应用

根据激光告警设备的作战对象和设备特点,分析了微弱激光探测技术应用于激光告警设备的主要限制因素,这些因素包括大视场接收和窄带光谱滤波技术之间的矛盾、光学系统通光孔径和视场角之间的矛盾、低激光重复频率的限制和激光信号的窄脉冲限制等;针对不同体制激光告警设备不同的灵敏度需求,简要介绍了在直接探测体制激光告警设备和散射截获体制激光告警设备采用的微弱激光辐射探测技术,这些技术包括低噪声探测器、低噪声光电接口电路和放大电路、双探测电路相关检测技术、大视场大相对孔径光学系统和大视场光谱滤波技术等,上述技术的应用,满足了激光告警设备的灵敏度需求。     

Remote sensing of penetrable objects buried beneath two-dimensional random rough surfaces by use of the Mueller matrix elements

The modified Mueller matrix elements for electromagnetic scattering from penetrable objects buried under two-dimensional random rough surfaces are investigated. This matrix relates the incident to the scattered waves, and it contains different combinations of the fully polarimetric scattering matrix elements. The statistical average of each Mueller matrix element is computed on the basis of the Monte Carlo simulations by exploiting the speed of the three-dimensional steepest-descent fast multipole method. The numerical results clearly show that relying only on the co-polarized or the cross-polarized intensities or both (i.e., vv, hh, vh, and hv) is not sufficient for sensing the buried objects. However, examining all 16 Mueller matrix elements significantly increases the possibility of detecting these objects. This technique can be used in remote sensing of scatterers buried beneath the rough ground.     

Millimeter wave imaging system for land mine detection

Applications using millimeter wave (mmW) and THz radiation have increased during the past few years. One of the principal applications of these technologies is the detection and identification of objects buried beneath the soil, in particular land mines and unexploded ordnances. A novel active mmW scanning imaging system was developed for this purpose. It is a hyperspectral system that collects images at different mmW frequencies from 90 to 140 GHz using a vector network analyzer collecting backscattering mmW radiation from the buried sample. A multivariate statistical method, principal components analysis, is applied to extract useful information from these images. This method is applied to images of different objects and experimental conditions.     

Spatial-Resolution Independent Object Detection Framework for Aerial Imagery

Earth surveillance through aerial images allows more accurate identification and characterization of objects present on the surface from space and airborne platforms. The progression of deep learning and computer vision methods and the availability of heterogeneous multispectral remote sensing data make the field more fertile for research. With the evolution of optical sensors, aerial images are becoming more precise and larger, which leads to a new kind of problem for object detection algorithms. This paper proposes the “Sliding Region-based Convolutional Neural Network (SRCNN),” which is an extension of the Faster Region-based Convolutional Neural Network (RCNN) object detection framework to make it independent of the image’s spatial resolution and size. The sliding box strategy is used in the proposed model to segment the image while detecting. The proposed framework outperforms the state-of-the-art Faster RCNN model while processing images with significantly different spatial resolution values. The SRCNN is also capable of detecting objects in images of any size.     

海底沉积层中高阶界面波对多掩埋物散射分析

根据界面波散射迭代公式,并利用含多个异质体弹性动力学的散射积分方程,引出海底沉积层中界面波高阶模式对掩埋物的散射情况。根据建立的分层海底模型,对沉积层中传播的界面波进行模式分解。利用界面波传播的Green函数构建界面波散射迭代积分,并根据弹性波对多异质体散射理论,将界面波散射积分推广到对多目标的散射情况。由模式分解的结果,求解出了前三阶界面波对多目标的散射情况,并对界面波高阶模式传播及对不同目标的散射情况做了分析。     

Ultrasound-modulated optical tomography of absorbing objects buried in dense tissue-simulating turbid media

Continuous-wave ultrasonic modulation of scattered laser light was used to image objects buried in tissue-simulating turbid media. The buried object had an absorption coefficient greater than the background turbid medium. The ultrasonic wave that was focused into the turbid media modulated the laser light that passed through the ultrasonic field. The modulated laser light that was collected by a photomultiplier tube reflected the local mechanical and optical properties in the zone of ultrasonic modulation. Objects buried in the middle plane of 5-cm-thick dense turbid media were imaged with millimeter resolution through the scanning and detecting alterations of the ultrasound-modulated optical signal. The optical properties of the dense turbid media included an absorption coefficient of 0.1 cm(-1) and a reduced scattering coefficient of 10 cm(-1) and were comparable with those of biological tissues in the visible and near-IR ranges. The dependence of the ultrasound-modulated optical signal on the off-axis distance of the detector from the optic axis and the area of the detector was studied as well.     

Low Frequency Vibrating Optical System for Detecting Objects Buried in Turbid Media: Preliminary Results

Preliminary results of an in-plane vibrating system to image objects buried in turbid media are presented. The incident optical beam is vibrated in a periodic back-and-forth motion at low frequency and small constant amplitude in a plane perpendicular to the direction of the beam. The detection is performed in the AC mode, blocking the DC component. The system shows a dramatic increase in the AC signal whenever the target boundary intersects with the reference line between the incident laser beam and a photodiode after a small aperture. The system was capable to render visible 2?mm width objects buried at depths up to 3?cm from the front surface of a 1% intralipid sample.     

白天用CCD摄象机对天体目标的探测及实验

文中介绍了用ＣＣＤ摄象机及相应的光学系统对天体目标的探测能力计算及白天用ＣＣＤ摄象机对天体目标的探测实验。给出了计算被测天体目标星等的计算表达式，指出白天在天空背景亮度在１２００ｃｄ／ｍ~２至２７００ｃｄ／ｍ~２时用普通低照度ＣＣＤ摄象机与大口径天文望远镜配合可探测到４至４．６等星