空气中快速运动声源水下声场的波数积分模型

本文采用二维波数积分，对空气中高速运动声源激发的水下声场进行建模。针对二维波数积分计算声场时域解计算量大的问题，提出一种快速计算方法。用本文提出的方法，对深海和浅海情况下，空气中高速运动单频点声源激发的水下声场进行了计算和仿真。计算结果表明：在深海，水下接收信号的幅度和瞬时频率随时间发生变化；接收器深度、接收器与声源运动轨迹的最小距离对接收信号的变化快慢有较大影响，而声源高度的影响较小；在浅海中，接收信号呈现快速的幅度起伏，明显的多普勒频移和大的频率展宽效应。与简正波方法相比，本文方法主要适用于近场计算，而简正波方法适用于远场。另外，当声源频率较高时，二维波数积分方法的计算量将迅速增大。     

Tracking-positioning of sound speed profiles and moving acoustic source in shallow water

An ensemble Kalman filter(EnKF) approach is proposed to perform sequential tracking of water column sound speed profile(SSP) using a moving acoustic source. First,the SSPs are discretized in depth and range, and are expressed by the empirical orthogonal functions(EOFs). Second, the acoustic source state information and the first three orders of EOF coefficients are expressed as the state variable, and the acoustic field information received by the vertical line array are the measured values. Successively, the state variables and measured values are used to establish the state-measure model. Last, the EnKF is utilized to track the state variables. The simulation results show that the root mean square error of SSP and the absolute error of source are all small, and thus the acoustic source tracking-positioning has high accuracy. Moreover, increasing the number of sample collection, the signal-to-noise ratio and the number of receiving elements can improve the tracking-positioning results. The method is verified using the experimental data of the East China Sea.     

Sound radiation into air by a point source moving underwater

Based on the discovery that the majority of radiated energy of a stationary sound source in shallow water is into the air at infrasonic frequencies, the sound transmission into air from a point source moving underwater is investigated in this letter. It is found that a moving sound source can radiate more acoustic energy into the air than a stationary one and the amount of energy radiated into the air increases with the speed of the moving source. Simulations show that the sound transmission into air is dominated by the inhomogeneous waves generated by the moving source.     

In search of a noncontact underwater acoustic source

The history of studies of the photoacoustic effect in liquids and its applications to the development of a “virtual” source of underwater acoustic signals is briefly reviewed. The problem of the efficiency of the photoacoustic conversion is considered. The modes of laser generation of sound, i.e., the thermooptical, nonlinear surface, and nonlinear bulk modes of operation, are discussed taking into account the real features of the marine environment, the most important of them being the surface waves. A review of the publications concerned with the problem of a moving photoacoustic source is presented. Advances in the photoacoustic underwater remote sensing technology are described.     

Efficient processing of acoustic signals for high-rate information transmission over sparse underwater channels

For underwater acoustic channels where multipath spread is measured in tens of symbol intervals at high transmission rates, multichannel equalization required for bandwidth-efficient communications may become prohibitively complex for real-time implementation. To reduce computational complexity of signal processing and improve performance of data detection, receiver structures that are matched to the physical channel characteristics are investigated. A decision-feedback equalizer is designed which relies on an adaptive channel estimator to compute its parameters. The channel estimate is reduced in size by selecting only the significant components, whose delay span is often much shorter than the multipath spread of the channel. Optimal coefficient selection (sparsing) is performed by truncation in magnitude. This estimate is used to cancel the post-cursor ISI prior to linear equalization. Spatial diversity gain is achieved by a reduced-complexity pre-combining method which eliminates the need for a separate channel estimator/equalizer for each array element. The advantages of this approach are reduction in the number of receiver parameters, optimal implementation of sparse feedback, and efficient parallel implementation of adaptive algorithms for the pre-combiner, the fractionally-spaced channel estimators and the short feedforward equalizer filters. Receiver algorithm is applied to real data transmitted at 10 kbps over 3 km in shallow water, showing excellent results.     

High-resolution angle-Doppler imaging by sparse recovery of underwater acoustic signals

The low resolution of Fourier two-dimensional spatial temporal spectrum estimation and the insufficient sample size of sonar space time sampling data often caused difficulties in high-resolution space time spectrum estimation. Aiming to solve this problem, we proposed a high-resolution angle-Doppler imaging method and designed an anti-reverberation space time filter based on the sparse recovery of underwater acoustic signals. The proposed imaging method established the spatial temporal sparse re...     

Characteristics of thermal acoustic radiation as a source of acoustic signals

A linear dependence of the output voltage of an acoustic thermometer on the temperature difference between the source and the piezoelectric transducer is demonstrated experimentally. The constant component of the output voltage is determined by the noise temperature of the receiving device. The main feature of the thermal acoustic radiation as a source of acoustic signals is that the signal is represented not by the total thermal radiation of the object, which is proportional to the absolute temperature of the latter, but by the part of this radiation that is proportional to the temperature difference between the object and the transducer.     

Effects of sound source location and direction on acoustic parameters in Japanese churches

In 1965, the Catholic Church liturgy changed to allow priests to face the congregation. Whereas Church tradition, teaching, and participation have been much discussed with respect to priest orientation at Mass, the acoustical changes in this regard have not yet been examined scientifically. To discuss acoustic desired within churches, it is necessary to know the acoustical characteristics appropriate for each phase of the liturgy. In this study, acoustic measurements were taken at various source locations and directions using both old and new liturgies performed in Japanese churches. A directional loudspeaker was used as the source to provide vocal and organ acoustic fields, and impulse responses were measured. Various acoustical parameters such as reverberation time and early decay time were analyzed. The speech transmission index was higher for the new Catholic liturgy, suggesting that the change in liturgy has improved speech intelligibility. Moreover, the interaural cross-correlation coefficient and early lateral energy fraction were higher and lower, respectively, suggesting that the change in liturgy has made the apparent source width smaller.     

Spatial correlation of hydroacoustic signals in a biaxial underwater sound channel

In the hydrological conditions of a biaxial sound channel, the cross-correlation between acoustic signals received at points spatially separated (from 10 to 63 km) along the sound propagation track is investigated. The signals are received by a narrow-beam array scanning in the vertical plane. The beam width is ～2° at the mean frequency (1 kHz) of a pseudo-noise signal. It is noted that, as the distance between the points of reception increases, the correlation decreases. This is mainly caused by the effect of the multipath propagation with an incomplete resolution of signals in arrival angles, rather than by changes in the “water” signal spectrum due to the attenuation.     

Image reconstruction of moving acoustic sound sources by temporal reference holography

The feasibility of applying temporal reference holography to detection of moving acoustic radiation sources are examined theoretically and experimentally. Temporal reference holography is proved to be used for the purpose if the width of amplitude spectrum of sound is within a certain range, because the point spread functions of temporal reference hologram coincide with amplitude spectra of sound waves used for recording them.     

水声信号处理领域新进展

本文介绍近30年来水声信号处理领域理论研究的新进展和在声纳设计中的应用。包括水声信号建模、声场匹配、海洋波导和内波现象的探索和研究、声矢量场信息获取和处理,低频水声信道的时/空相关特性,水下目标辐射噪声的不变特征量提取和检测技术,水下语音、图像传输和抗干扰技术。同时概述,声纳设计的前沿领域:大孔径拖曳线列阵声纳、高分辨力合成孔径声纳、深海传呼机等的发展情况。     

海洋声学环境下水中声源的时延估计法定位精度分析

水中声源的定位精度受到海洋声学环境的重要影响。结合海上试验的实际应用,分析了水下观测平台采用时延估计法对声源的定位精度问题。根据理论分析,计算了时延估计误差、海洋中声速不均匀、平台非稳性、及声传播起伏等因素引起的俯仰角和方位角误差。利用误差传递公式,获得了上述因素引起的不同平台深度下,不同距离声源的定位误差。比较了采用平面阵与立体阵、是否补偿声线弯曲效应等条件下定位误差的变化,并通过海上试验结果进行了部分验证。研究结果表明,海洋声速不均匀对定位误差的贡献最大。采用立体阵代替平面阵、测量海洋声速剖面并补偿声线弯曲引起的定位误差,在1000m距离上可使定位相对误差从最大30%降低到约10%,有效提高了较远距离上的定位精度。研究结果对于采取措施提高水中声源的定位精度有指导意义。     

可变参数水声发射系统

本文给出了一种完整的供水声通信、数传、遥测、遥控以及水声传播研究用的水声发射系统，包括可编程信号源，高效功率放大器和宽带高效发射换能器等部分，具有良好的功能和实用价值。     

Experimental estimation of the parameters of a sphere by high-frequency chirped underwater sound pulses

For a sphere moving under the sea’s surface in shallow water, the possibility of its tomographic observation by measuring the scattered high-frequency sound pulses is considered. To raise the spatial resolution and] sensitivity of the method, the received sound signals are subjected to filtering matched with the transfer characteristic of the waveguide. Ways of increasing the robustness of the solution to the inverse problem by using different decision criteria are discussed.     

Correlation of underwater acoustic signals simultaneously received by omnidirectional and directional means

A comparison of experimental data on the spatial correlation between acoustic signals simultaneously received by an omnidirectional hydrophone and a directional vertical array is carried out. The spatial correlation was measured between the signals received at different distances in a deep ocean. The points of reception were positioned in two convergence zones along the path of sound propagation with a point-to-point distance of about 64 km. Pseudonoise signals were emitted in the frequency range (0.8–2.0) kHz and received by a vertical array, whose beam had a width of ∼2°. Concurrently, multipath signals received with the central hydrophone of the array were recorded. Signals in the first and second convergence zones were received at different times. Nevertheless, in the case of the directional reception, the coefficients of spatial correlation between such signals appeared to be as high as 0.64–0.74 even under the conditions of incomplete resolution of signals in the angle of arrival in the vertical plane. At the same time, in the case of omnidirectional reception, the coefficients of spatial correlation were below 0.32.     

Passive ranging of a moving sound source using three-dimensional measured information

To solve the problem of passive ranging of a moving sound source,a method of estimating the initial distance of target is presented by using the measured inform...     

Estimation of the location of a farfield acoustic source

A backward integration method for estimating the location of a source of sound waves in the atmosphere is presented. This geometric acoustics method is based upon the analysis of microphone array measurements to determine the incoming ray direction in three dimensions. The equations governing the propagation of the ray are then integrated backward in time. The sound source lies somewhere along the calculated ray path. The intersection of such loci from more than one array would provide an estimate of the source location. The method appears to be very rapid to implement and, assuming the time delays to be accurately measured, limited in accuracy only by the timeliness of the input sound speed and velocity profiles in the atmosphere.     

Estimation of the relaxation parameters of a cholesteric liquid by the parameters of acoustic streaming

The possibility of determining the relaxation time of cholesteric liquid crystals with a large helix pitch from the parameters of acoustic streaming is demonstrated experimentally.     

Regional distinctions in the time structure of the sound field produced by a point source in the underwater sound channel

Experimental data on long-range propagation of explosion-generated signals in different ocean regions are analyzed. The objective of the analysis is to reveal the regional distinctions in the time structure of the sound fields in the underwater sound channel and to demonstrate the following frequently observed phenomena: splitting of signals in the “classical” quartets, noise background in the quartets, and deviation of the frequency-independent phase shift between signals in the quartets from the expected value (a multiple of 90°) due to the contact with a caustic. Possible mechanisms of these phenomena are discussed.     

声源作圆周运动时的多普勒效应

利用自制装置演示了声源作圆周运动的多普勒效应，并应用图谱分析软件得到频率分布图。