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961.
This paper describes a new framework for object detection and tracking of AUV including underwater acoustic data interpolation, underwater acoustic images segmentation and underwater objects tracking. This framework is applied to the design of vision-based method for AUV based on the forward looking sonar sensor. First, the real-time data flow (underwater acoustic images) is pre-processed to form the whole underwater acoustic image, and the relevant position information of objects is extracted and determined. An improved method of double threshold segmentation is proposed to resolve the problem that the threshold cannot be adjusted adaptively in the traditional method. Second, a representation of region information is created in light of the Gaussian particle filter. The weighted integration strategy combining the area and invariant moment is proposed to perfect the weight of particles and to enhance the tracking robustness. Results obtained on the real acoustic vision platform of AUV during sea trials are displayed and discussed. They show that the proposed method can detect and track the moving objects underwater online, and it is effective and robust. 相似文献
962.
Advantages of Using Multichannel Analysis of Love Waves (MALW) to Estimate Near-Surface Shear-Wave Velocity 总被引:2,自引:1,他引:1
Jianghai Xia Yixian Xu Yinhe Luo Richard D. Miller Recep Cakir Chong Zeng 《Surveys in Geophysics》2012,33(5):841-860
As theory dictates, for a series of horizontal layers, a pure, plane, horizontally polarized shear (SH) wave refracts and reflects only SH waves and does not undergo wave-type conversion as do incident P or Sv waves. This is one reason the shallow SH-wave refraction method is popular. SH-wave refraction method usually works well defining near-surface shear-wave velocities. Only first arrival information is used in the SH-wave refraction method. Most SH-wave data contain a strong component of Love-wave energy. Love waves are surface waves that are formed from the constructive interference of multiple reflections of SH waves in the shallow subsurface. Unlike Rayleigh waves, the dispersive nature of Love waves is independent of P-wave velocity. Love-wave phase velocities of a layered earth model are a function of frequency and three groups of earth properties: SH-wave velocity, density, and thickness of layers. In theory, a fewer parameters make the inversion of Love waves more stable and reduce the degree of nonuniqueness. Approximating SH-wave velocity using Love-wave inversion for near-surface applications may become more appealing than Rayleigh-wave inversion because it possesses the following three advantages. (1) Numerical modeling results suggest the independence of P-wave velocity makes Love-wave dispersion curves simpler than Rayleigh waves. A complication of “Mode kissing” is an undesired and frequently occurring phenomenon in Rayleigh-wave analysis that causes mode misidentification. This phenomenon is less common in dispersion images of Love-wave energy. (2) Real-world examples demonstrated that dispersion images of Love-wave energy have a higher signal-to-noise ratio and more focus than those generated from Rayleigh waves. This advantage is related to the long geophone spreads commonly used for SH-wave refraction surveys, images of Love-wave energy from longer offsets are much cleaner and sharper than for closer offsets, which makes picking phase velocities of Love waves easier and more accurate. (3) Real-world examples demonstrated that inversion of Love-wave dispersion curves is less dependent on initial models and more stable than Rayleigh waves. This is due to Love-wave’s independence of P-wave velocity, which results in fewer unknowns in the MALW method compared to inversion methods of Rayleigh waves. This characteristic not only makes Love-wave dispersion curves simpler but also reduces the degree of nonuniqueness leading to more stable inversion of Love-wave dispersion curves. 相似文献
963.
介绍“中国大陆构造环境监测网络”GNSS基准站观测数据的处理和分析.数据处理基于陆态网工程2010-07-01 -2012-03-16日的252个GNSS基准站观测数据,获得了基准站的坐标单日解时间序列,利用抗差最小二乘估计拟合出了这些站的速度场. 相似文献
964.
斑岩型铜(钼)矿床和斑岩型钼(铜)矿床是世界钼资源最主要的来源,提供的钼金属量相当。对比发现,两类矿床在流体来源演化以及铜和钼的相关性上较为相似,而在铜/钼比值、品位、矿物共生组合、蚀变类型等方面存在差异,特别是斑岩铜(钼)矿初始出溶流体中的Cl-/F-值、硫的总量、SO2/H2S以及H+/ K+比斑岩钼(铜)矿高。流体演化过程中有两方面因素可能影响最终沉淀的铜和钼比值:(1)铜和钼在流体中的性质差异,如铜以氯或硫络合物形式运移,沉淀受温度影响比较显著,钼以羟基或氯络合物形式存在,沉淀受压力控制比较明显;(2)流体自身氧逸度、pH、硫逸度的变化以及演化路径的改变。然而,和初始流体性质的差异相比,流体演化过程对最终形成矿床类型的影响是有限的,决定矿床形成斑岩铜(钼)矿化还是钼(铜)矿化的因素可能在流体出溶之前的岩浆起源演化阶段就存在。斑岩铜(钼)矿常分布在偏挤压的陆缘弧和大陆碰撞造山带环境,基底多为新生或加厚的陆壳,斑岩钼(铜)矿多出现在偏伸展的陆内裂谷、弧后及造山后伸展环境,基底可以为老陆壳或新生的陆壳;上述特征反映物源区或岩浆的起源和演化方式不同可能是制约形成斑岩铜(钼)矿还是钼(铜)矿的主要机制。 相似文献
965.
966.
由于美国帕克菲尔德地震的发生以及地震预测研究的进展,经过数年沉寂之后,国际上对地震预测的讨论又处于增温状态。 相似文献
967.
968.
As a kind of transportation mode for crossing channels,undersea tunnel has incomparable advantages for its directness,convenience,fastness,insusceptibility to weather conditions,and smaller influences on environments.In recent years,with the development of undersea tunnel construction,the design and construction technologies have been greatly enhanced.The first undersea tunnel in China has just been built.Waterproofing is the key technique of undersea tunneling.A new concept of waterproofing scheme of grouting,sealing,draining and divided sections was adopted in the construction of the tunnel based on the researches,the in-situ geological features,the astuteness of the current technology,and the cost of construction.The structural details of the sealing and draining system are introduced to illustrate the salient features of the new waterproofing technique.It is hoped that experiences described in the paper can offer guidance for the construction of the extensive undersea tunnels in the coming years. 相似文献
969.
970.
自适应Chirplet变换及其在探地雷达目标探测中的应用(英文) 总被引:4,自引:2,他引:2
探地雷达不仅能够探测金属目标体,而且能够探测非金属目标体,而成为UX0和地雷探测的一种重要的浅部地球物理方法。但是在地雷和UX0探测中,目标体埋藏深度浅,在探地雷达数据信噪比较低情况下,地表和土壤层的反射严重干扰对目标体的拾取。本文采用自适用Chirplet变换来消除地表层和土壤层变化的干扰,并在Radon—Wigner分布的基础上,采用自适用Chirplet变换来拾取目标体的信号。通过对实际探测实验数据应用证明,本方法处理结果比传统的偏移方法具有较高的信噪比,并能清晰地提取目标体信号。 相似文献