空间过滤简正波的模拟实验研究

在侧壁无消声的波浪槽(70×2×0.6m~3)内,利用9根有水平指向性的长圆管换能器作阵元,实现了前四号简正波的空间过滤,定性地研究了简正波过滤阵抑制近场点源干扰的理论概念,并对起伏波浪表面对各号简正波振幅起伏的影响作了初步观察。     

一种低声速沉积层海底参数声学反演方法

软泥底环境下沉积层参数的声学反演是国际水声领域的一个研究热点.浅海中,当高声速基底和海水之间存在一层低声速(小于海水声速)的沉积层时,小掠射角情况下不同频率声传播损失会出现周期性增大现象.基于此现象,提出一种适用于低声速沉积层的海底参数声学反演方法.首先,推导给出小掠射角情况下传播损失周期增大的频率间隔与沉积层声速、厚度及近海底海水声速之间的解析表达式;其次,利用一次黄海实验中软泥底环境下的宽带声传播信号,提取了小掠射角下传播损失增大的频率周期;再次,把该解析表达式作为约束条件,结合Hamilton密度与声速的经验公式,采用匹配场处理反演给出沉积层的声速、密度、厚度及基底的声速、密度;然后,利用声传播损失数据反演得到泥底环境下不同频率的声衰减系数,通过拟合发现泥底声衰减系数随频率近似呈线性关系;最后,给出了双层海底模型和半无限大海底模型等效性的讨论.反演结果为低声速沉积层海底声传播规律研究与应用提供了海底声学参数.     

浅海平均声场角度谱分析法与回波混响比的距离、深度结构

浅海平均声场角度谱分析法以Ray-mode理论为基础。引进平均声场角度谱的概念以后,可使浅海传播衰减、远程混响和空间相关等平均特性的一些计算变得较为简单。用该法在浅海负梯度和均匀层情况下,计算了远程混响和回波、混响比的距离、深度结构。理论证明,在非均匀层浅海远程探测中,深度可变声呐比固定声呐有较为明显的优越性。本方法和结果将有助于分析小掠角海底(面)散射的角度、频率依赖关系。     

LONG-RANGE REVERBERATION AND BOTTOM SCATTERING STRENGTH IN SHALLOW WATER

According to the method of angular power spectrum for averaged sound field in shallow water,the transformation relation between arbitrary angle dependence of hottom scattering and the rangedependence of long-range reverberation in shallow water homogeneous layer is established.Ascompared with the conventional model of boundary reverberation at short range in deep sea,a multipath correction factor is added.By using the transformation relation,the bottombackscattering strength for the frequency band of 0.8—4.0kHz and grazing angle range of 2—10°has been derived from shallow-water reverberation data at five locations in the Yellow Sea,theBobai Sea and the East China Sea.It is shown that the bottom scattering constant(μ)and theangle index(2n)for high speed sediment of the continental shelf depend not only on sea area andfrqucncy,but also on angle range.     

浅海远程混响与海底散射强度

利用浅海平均声场角度谱分析法,在海底散射的任意角度关系和浅海均匀层远程混响的距离关系之间建立了变换关系。与国外沿用的深海近程界面混响理论相比,多了多途传播修正因子K(公式18)。利用该变换关系式,由黄海、渤海、东海等5个海区的浅海远程混响资料,推得频率为0.8—4kHz,掠射角为2—10°的低频、小掠角海底散射强度。所得结果与国外深海直接测量的大掠角数据衔接较好。结果同时表明,大陆架高声速海底散射常数(μ)和角度指数(2n)不仅与海区、频率有关,而且与角度范围有关。在掠角很小时,海底散射强度随掠角减小比中等掠角时衰减更快。     

THEORETICAL ANALYSIS OF THE BOUNDARY REFLECTION LOSS AND THE PARAMETER EXTRACTION AT SMALL GRAZING ANGLE

It has been shown that for"high speed"sediment the effects of layered structure of the sedimentare not significant for a certain range of frequency at small grazing angle,and the reflection behaviorapproaches to the Rayleigh reflection specifled by the surficial sediment pararneters(p,c,a).In thatcase the frequency dependence of reflection loss is mainly due to scattering of the surface roughness.If the scattering loss is considered by using the Bass perturbation theory,the reflection loss at smallgrazing angle can be written as: -In|νφ={Q_0(p,c,a)+Q_1(f,σ)}φwhere Q_0 is the term due to Rayleigh loss independent of frequency,Q_1 is the term due to scatteringloss depending on frequency f and the spectral density of surface roughness.Some experiments,from which parameter Q can be extracted,are analysed.It is found,that in given frequency range(0.5—3.0kHz)the magnitude and the tendency of variation of the parameter Q extracted fromdiffernt experiments are distributed in the permissible region predicted     

小掠射角边界反射损失的理论分析及参数提取问题

对于高声速海底在一定的频率范围内,小掠角的反射特性将不受分层结构的影响,反射特性趋于由表层参数(ρ,c,a,)所表征的瑞利反射。此时,反射损失的实际频率关系应主要归因于粗糙表面的散射,考虑Bacc微扰理论的散射后,可将小掠角反射损失表为下列模型: —ln│V(φ)│={Q_0(p,c,a) Q_1(f,σ)}φ其中Q_0项代表瑞利损失。Q_1项代表散射损失,依赖于具体的粗糙度谱函数。分析了与提取参数Q有关的一些实验,并相应提取了Q值,在一定的频率范围内(0.5—3.0kHz)所提取的Q值无论其量值或变化趋势均基本分布在按上述机制分析预计所允许的范围之内。     

浅海声场垂直相关与边界反射(散射)损失

在浅海均匀层中,利用三参数海底声学模型,引进声传播有效掠角的概念,推导了声场垂直相关与边界损失等参数的关系;提出了大面积测量低频小掠角海底反射(散射)损失的方法;在0.4—3.15kHz频段内测量了小掠角0.7—15°范围内的边界反射(散射)损失;根据本文结果及有关资料,可以较好地解释浅海平均声场过渡距离随频率的变化。