【作者】 张明辉；

【导师】 孙辉；

【作者基本信息】 哈尔滨工程大学 ， 水声工程， 2011， 博士

【摘要】 海洋中存在大量的散射体,入射声波投射到这些散射体上会产生散射,而这些散射声波在接收点的迭加就形成了混响。在水平有界海域,海洋混响受水平边界的影响严重；同时,近岸浅海的渐深海底也影响海洋混响的规律,本文题目所指的“不规则海域”,就是此类水平边界和海底边界形状不规则并且边界条件复杂的海域,不规则海域中的混响有其特殊的规律。混响是主动声探测的重要干扰背景,研究在不规则海域中的主动声纳探测问题,要求对不规则海域中混响场的特性有充分了解,才能针对该类海域声场及声干扰场特点,开发有效的水声探测技术。在浅海,海底混响是海洋混响的重要组成部分,而海底散射强度又是影响海底混响的重要因素,随着多基地声纳系统的研究和应用,就需要研究海底散射强度与入射掠射角、散射掠射角和散射方位角的关系,即海底三维散射强度。基于此,本文主要研究海底三维声散射强度的测量方法以及不规则海域的混响特性。本文给出了一种测量海底三维散射强度的方法,该方法由水平指向性窄垂直指向性宽的声源发射信号,在接收位置由水平、垂直指向性窄的T型接收阵接收散射区域中的某散射元的海底散射信号,根据入射声程和散射声程计算的传播损失、声源的声源级和接收到散射信号声强,计算可得距此散射元单位距离处的入射声强和散射声强,再根据散射强度定义可求得此散射元的三维散射强度。用时延波束形成技术改变T型接收阵的声轴指向方向,使声轴指向散射区域的其它散射元,用相同的方法可求得该散射点的三维散射强度,进而能测得整个散射区域中各散射元的三维散射强度。文中还引入一计算海底三维散射强度的理论模型,该模型是在海底散射是各向同性这一假设条件下建立的。湖上测量得到的湖底三维散射强度同理论模型计算得到的结果相吻合,但在海试中,相同的入射掠射角、散射掠射角和散射方位角条件下海底同一散射元在不同入射方向上测量得到的前向散射强度有近20dB的差别,表明实验海域海底散射强度各向异性。以射线声学理论为基础,在收发合置情况下,用Lambert散射定律计算海底散射强度,只需考虑海底的一次散射对混响强度的贡献,对倾斜海底混响强度进行建模与实验验证；在收发分置情况下,用三维散射模型计算海底散射强度,同样只需考虑海底的一次散射对混响强度的贡献,对倾斜海底收发分置混响强度进行建模与实验验证。在此基础上,通过几何变换关系,可用倾斜海底混响强度模型计算不规则海域侧面壁的混响强度,再将左侧壁面、右侧壁面和海底这三个粗糙面的混响强度迭加起来即得不规则海域总混响强度,并通过实验数据验证了模型的正确性。通过理论计算,在收发合置的情况下,由于有两侧面壁的影响,不规则海域的混响强度在近程要略大于水平海底和倾斜海底的混响强度,随时间的衰减也快。对于不规则海域混响强度,发射声源的发射脉宽对混响强度的影响较大,脉宽越宽,混响强度越大；海底倾角和两侧面壁开角对远程混响有较大影响,海底倾角越大,混响强度随时间的衰减越快,两侧壁开角越大,混响强度随时间的衰减越慢；两侧面壁倾角越小,不规则海域近程混响强度越大,远程混响强度越小。以海底散射系数的空间相关半径设定散射单元面积,根据混响产生的物理过程,建立海底多途混响信号模型,通过对仿真得到的混响信号进行统计分析,其瞬时幅值服从高斯分布,瞬时相位服从(0,2π)间的均匀分布,符合混响的一般统计规律。通过对仿真得到的不规则海域收发分置多途混响信号和实验得到的不规则海域混响信号的处理知,不规则海域混响垂直方向上的空间相关性比水平方向上的空间相关性强；而在水平方向上,垂直于两侧面壁方向上的空间相关性比平行于两侧面壁方向上的空间相关性强。随着混响信号频率的增高,各方向上的空间相关性减弱,并且垂直方向上混响的空间相关性变化较水平方向上的混响空间相关性变化明显。更多还原

【Abstract】 There are a lot of scatterers in the ocean, so that when acoustic waves projected into this uneven media, it will have scattering. The sum total of the scattering contributions from all the scatters is called reverberation. Shore near the port in the gulf or in the sea area between the islands is very important. Reverberation in this irregular sea area has important infection by the shore and islands, and at the same time, the gradual deeply wedge shaped bottom also affect the reverberation rule. The irregular sea is the sea area with irregular horizontal and bottom boundary shapes and the complicated boundary conditions. Reverberation intensity in irregular sea has its own rule. The reverberation is one of the main interference factors for active sonar system, and the properties of reverberation in irregular sea area should be comprehended sufficiently when the problem about the detection with active sonar in irregular sea areas is researched. In shallow water, the bottom scattering strength is an important factor for bottom reverberation, and bottom scattering strength is an important parameter for bottom reverberation. With the development of the bistatic sonar system, research on bottom scattering strength with different incident grazing angle, scattered grazing angle and scattered azimuth angles is necessary. So the paper is focused on the investigating measurement method of three-dimensional bottom scattering strength and the properties of irregular sea area reverberation.A method for measured bottom three-dimensional scattering strength is given in the paper which can measure sector scattering area three-dimensional bottom scattering strength. T-receiving array which has narrow horizontal directivity and narrow vertical directivity receives scattering signal from the bottom scattering unit when transmitting transducer which has wide vertical directivity and narrow horizontal directivity transmits CW pulse signal. The three-dimensional scattering strength of the bottom scattering unit could be calculated with the transmission loss which could be got with incident path and scattering path, the source level of transmit acoustic source and the strength of scattering signal. In use of the technique of phase shift beam forming the acoustic axis could be pointed to another bottom scattering unit in scattering area, then the three-dimensional scattering strength of this scattering unit could be calculated. Further more the three-dimensional scattering strength of other units in scattering area would be known. The measurement method proposed in this paper is proved feasible because the result in theory accordance with the result of dealt data of examination on lake well. But from the result of dealt data of sea trial, the bottom scatter is anisotropy. By ray acoustics theory, the irregular sea monostatic reverberation intensity simulation model is established by using Lambert’s law to calculate scattering strength of the bottom and lateral wall. The monostatic reverberation intensity of the simulation model is in consistent with the reverberation intensity of the experimental data. And by ray acoustics theory, the incline seafloor bistatic reverberation intensity simulation model is established by using three-dimensional scattering model to calculate bottom scattering strength. The bistatic reverberation intensity of the simulation model is in consistent with the reverberation intensity of the experimental data. The conclusion that the irregular sea area monostatic reverberation intensity is bigger than horizontal seafloor monostatic reverberation intensity and oblique seafloor monostatic reverberation intensity and the decaying speed of the irregular sea area reverberation intensity is faster than horizontal seafloor monostatic reverberation intensity and incline seafloor monostatic reverberation intensity would be got by theoretical calculation. For irregular sea area reverberation, the transmit pulse width and horizontal beam width of source make a big affection. The reverberation increases with the pulse width and beam width. The seafloor tilt angle and the open angle of two lateral walls mainly influence long-distance reverberation. The reverberation intensity decays with time faster with the tilt angle bigger and the open angle smaller. The tilt angle of two sides influences the short-distance reverberation intensity heavily.The simulating model of mulpi-path bottom reverberation signal, developed by means of the generating process of the bottom reverberation, based on the Ray theory, using the element scattering model, has been built. It plots out the scattering element by the bottom scattering coefficient correlation radius and it has a very definite physics sense. It can be concluded from the simulating reverberation signals that the instantaneous amplitude is submitted to Gauss distribution and the instantaneous phase is submitted to uniform distribution between (0,2π). The comparison result of simulating reverberation signals of irregular sea area with experimental reverberation signals shows that vertical spatial correlation is stronger than horizontal spatial correlation. What is more, on the horizontal direction the spatial correlation of upright to the two lateral walls is stronger than the parallel’s. Both vertical spatial correlation and horizontal spatial correlation decrease with reverberation signal frequency increase and the vertical spatial correlation changes more distinctness than horizontal.更多还原