Application and measurement of underwater acoustic reciprocity transfer functions in reverberant sound field

The reciprocity measurement theory in anomalous reverberant sound fields was investigated.An improved method Was proposed due to the interrelated errors.The source volume velocity Was corrected by spatial average of measurement results and evaluation of the reverberant sound field influence on acoustic energy density.The result was validated in underwater experiment,corrected reciprocity measurement results were almost the same as direct measurement results.It indicates that reverberant sound field does not affect the validitv of the principle,but influences the obtainment of source volume velocity,then influences the measurement of transfer functions with the principle.The proposed method is simple and effective in anomalous reverberant sound fields.The study mav be valuable for the applications which are based on the principle.     

Using the system function to analyze the performance of transducer’s impedance measurement method

Prom investigation of the advantages and disadvantages of conventional tri-voltage method,a method for the measurement of the transmitting transducer’s impedance was presented to solve the difficult problem of examining the consistency of the transmitting phased array on the single-mode excitation sea spot.In the method based on the system function, the circuit structure of tri-voltage method was used but new parameters were measured.The principle of the method was given first.Then when resistors with different nominal values were used in the circuit,the measured results for the impedance of transducers were reported.The results were compared with the higher precision impedance analyzer.Finally,the error analysis was performed according to the impedance formula and the equivalent circuit parameters were fitted.Under the condition of guaranteeing the sampling precision,by performance analyzing, the resistor value in series was chosen relatively smaller than the impedance of transducer,the measurement of impedance could achieve the same precision as the higher precision impedance analyzer.Finally,the least squares curve-fitting of measured curves indicated that the transducer equivalent electrical parameters could be extracted accurately and used to design the matching network.     

A three-step system calibration procedure with error compensation for 3D shape measurement

System calibration, which usually involves complicated and time-consuming procedures, is crucial for any three-dimensional （3D） shape measurement system based on vision. A novel improved method is proposed for accurate calibration of such a measurement system. The system accuracy is improved with considering the nonlinear measurement error created by the difference between the system model and real measurement environment. We use Levenberg-Marquardt optimization algorithm to compensate the error and get a good result. The improved method has a 50% improvement of re-projection accuracy compared with our previous method. The measurement accuracy is maintained well within 1.5% of the overall measurement depth range.     

The parametric source method for measuring characteristics of underwater acoustic materials in a pressure vessel

A truncated broadband parametric array with a primary frequency of 500 kHz and difference frequency range of 1 kHz to 30 kHz was designed as a sound source of the underwater acoustic material measurement system.By analyzing the theoretical calculation and actual measurement results in array directivity of the truncated broadband parametric source at typical frequencies,we observed that the curves of the two results were basically consistent,which proved that the calculation model was correct.Application of bell-shaped short-duration pulse to achieve broadband measurement for characteristics of underwater acoustic materials was beneficial to reduce the effects of diffraction from the panel edges.The measurement system was established for measuring the sound pressure reflection coefficients,sound pressure transmission coefficients and absorption coefficients of the large panel sample in the pressure vessel.The size of this tank is φ4 m×12 m,the maximum hydrostatic pressure is 4.5 MPa,and the corresponding measuring frequency range is from 1 kHz to 30 kHz.The measured curves had a good agreement with theoretical curves,which verified that the parametric source measurement method was feasible.Then,the sound absorption properties of the rubber plate sample were measured under different hydrostatic pressures.The studying results could show that the parametric source measurement method had the potential application in the limited space water,such as the pressure vessel.     

Correction for the diffraction loss in the ultrasonic attenuation measurement in VHF range

Two silicate glasses which have different acoustic properties and different thickness, were taken as the specimens, their frequency dependences of the longitudinal attenuation coefficients were measured in the frequency range of 50 to 300 MHz by the pulse reflection method, and the diffraction loss included in the measurement was corrected by theoretical calculation using A. O. Williams' expression. It has been shown that the measurement error of attenuation coefficient due to diffraction loss could be corrected very well by this method, regardless of the thickness of specimens.     

Research of measurement errors caused by salt solution temperature drift in surface plasmon resonance sensors

Influence of temperature on measurement of surface plasmon resonance (SPR) sensor was investigated. Samples with various concentrations of NaCl were tested at different temperatures. It was shown that if the affection of temperature could be neglected, measurement precision of salt solution was 0.028 wt.-%. But measurement error of salinity ca,used by temperature was 0.53 wt.-% in average when the temperature drift was 1 ℃. To reduce the error, a double-cell SPR sensor with salt solution and distilled water flowing respectively and at the same temperature was implemented.     

Shape measurement of aspheric plastic lens with large angle

In this paper, according to the features of easy distortion and scratch for aspheric plastic lens, a noncontact measuring method is raised to test error in shape of the lens. Namely, the distance between a template and its image reflected with tested lens can be measured in nearly the vertical direction of the lens axis when the two-dimensional (2D) template is put near the measured surface. Then, the outline of the central cross-section could be obtained by calculating and curve fitting. Furthermore, three-dimensional (3D) surface can be imitated through rotating the component. A new fitting method of drift measurement is presented to prevent reducing precision when the lens and the template are fixed. The template is adjusted according to the position of the lens. The measurement precision is in the order of magnitued of sub-microns. Rotationally symmetric convex aspheric surface with any angle can be measured by this method.     

Research of measurement errors caused by salt solution temperature drift in surface plasmon resonance sensors

Influence of temperature on measurement of surface plasmon resonance (SPR) sensor was investigated.Samples with various concentrations of NaCI were tested at different temperatures. It was shown that if the affection of temperature could be neglected, measurement precision of salt solution was 0.028 wt.-%.But measurement error of salinity caused by temperature was 0.53 wt.-% in average when the temperature drift was 1 ℃. To reduce the error, a double-cell SPR sensor with salt solution and distilled water flowing respectively and at the same temperature was implemented.     

Signal processing in underwater acoustic communication system for manned deep submersible "Jiaolong"

For the first time in the world,underwater acoustic transmission of images,human voice,data and texts between vehicle under 7000 m depth and surface ship was accomplished by underwater acoustic communication system of manned deep submersible "Jiaolong".In this paper,signal processing in underwater acoustic communication system for manned deep submersible "Jiaolong" is introduced.(1) Four communication methods are integrated to meet different needs:1) coherent underwater acoustic communication,with a variable transmission rate from 5 kbps to 15 kbps,to transmit images.2) Non-coherent underwater acoustic communication, with a transmission rate 300 bps,to transmit texts,instructions,and sensor data. 3) Spread spectrum underwater acoustic communication,with a transmission rate 16 bps,to transmit instructions.4) Underwater voice communication,using single sideband modulation to transmit human voice.(2) Signal processing method in coherent communication mainly consists of concatenation of decision feedback equalizer and Turbo decoder,and wavelet based image compression with fixed length coding.In the equalizer,Doppler compensation,multichannel combining and equalizer coefficients updating are all using fast self-optimized adaptive algorithm.(3) A linear hydrophone array is lowered from the mother ship to certain depth, and spatial diversity combining technology is adopted.(4) Diving trials of "Jiaolong" were carried out in Pacific Ocean.The communication range can cover nearly all ocean depth.One optical/acoustic image can be transmitted in 7 or 14 seconds.     

A restraining multipath effect method for the measurement of insertion loss of underwater acoustic materials

A method suppressing multipath effect when measuring the underwater acoustic materials in a reverberant field is proposed, which is called "virtual end-fire array method".To weaken the coherence of the same-frequency reflection interference of each path, signal of different phases at different positions was transmitted by a single transducer in the simulation design, and a sharp directionality in the direction of the array length was formed. All signals at the above positions were superimposed to eliminate the clutters. The insertion loss(IL) of the material was finally calculated by extracting the desired waveforms. In the measured frequency range of 3–20 k Hz, the aluminum plate with size of 1.1 m × 1.0 m × 8 mm and the round aluminum plate with 0.5 m in diameter and 8 mm in thickness were measured in a reverberant tank with size of 5.5 m × 3.5 m × 3.5 m. Results showed the measured lowest effective frequency limit can be reduced by the virtual end-fire array technique compared with the conventional method.In the measurement of round aluminum plate and rectangular aluminum plate, errors in the effective measurement band was less than 0.5 d B and the interference of the acoustic multipath propagation effects was reduced effectively. The ability of the transducer in reverberant tank to measure acoustic materials has been improved after implementing this method.     

扫描深度误差对声图测量的影响及其修正方法研究

声图测量技术是一种适用于近场的精确被动定位技术。为了提高测量精度,分析了扫描深度误差对声图测量的影响,并提出了修正方法。通过理论分析表明对于过阵航行过程,当扫描深度大于目标声源实际航行深度时,误差可以被修正,并可测得目标声源的实际过阵深度;而当扫描深度小于目标实际航行深度时,误差将不能被修正。用理论分析结果处理仿真及海上实验数据,修正效果良好且与理论分析一致。      

近场浅海舰船目标定位精度实验研究

根据聚焦波束形成声图处理方法在实际海上测量的特点,提出用系统时延差校准、基阵倾角修正、深度测量、分频段目标定位等多种方法克服测量系统及环境的各种不利因素,实现舰船目标高精度定位。采用声图计算结果与GPS记录值对比、声图计算结果与GPS记录值的正横距对比两种方法进行了聚焦波束形成声图法精度的实验验证,经验证聚焦波束形成声图处理方法在浅海测量区有较高的定位精度。其最大正横距差值可以达到2.9 m,均值0.93 m,从而实现舰船目标高分辨精确定位。      

基于实孔径成像的水下高速小目标末弹道 测量方法

在没有合作声信标和水下弹道测量系统配合的条件下,传统的基线定位法难以测量水下高速小目标末弹道。文中提出了一种测量高速小目标末弹道的方法,该方法通过在靶标上安装实孔径声学成像系统,发射双曲调频信号保持系统在目标回波多普勒偏移量较大时的输出幅值稳定,并采用频域宽带信号处理技术修正多普勒偏移造成的目标方位测量误差和抑制混响干扰,经过湖上试验,系统获取了较清晰的声学图像,准确分辨出目标位置,能够较精确地测量高速小目标末弹道。     

Sub-pixel dimensional measurement with Logistic edge model

To separate substandard workpieces from products, sub-pixel edge location with Logistic edge model is proposed for dimensional measurement. In the first step, workpiece rotation is corrected with high precision image rotation to reduce the measurement error and simplify the edge model. Secondly, Logistic edge model is utilized for fitting the discrete edge data to locate the sub-pixel workpiece edge and model parameters are estimated through the objective function in terms of the difference between assumed model and real image data. Finally, an edge pixel compensation method is presented with edge pixel compensation value, which weakens the effect of edge transition zone effectively. Experimental results demonstrate that the proposed method is effective for dimensional measurement with the relative error less than 0.05%.     

载人潜水器“蛟龙”号的水声通信信号处理

蛟龙号的水声通信机实现了世界上首次7000 m深度的潜器与母船间的图像、语音、数据和文字的水声通信传输。研究了适用于载人潜水器的水声通信信号处理。(1)它有4种通信功能:1)相干水声通信,传输速率为5~15 kbps,用于传输图像;2)非相干水声通信,传输速率300 bps,传输文字、指令和数据;3)扩频水声通信,传输速率16 bps,传输指令;4)水声语音通信,采用单边带调制技术传输语音。(2)相干水声通信信号处理方法主要是自适应多普勒补偿的多通道自优化判决反馈自适应均衡器,它与Turbo码级联工作,同时采用定长编码的小波图像压缩方法。(3)声呐线阵吊放至水中一定深度,实现空间分集合并技术。(4)太平洋水域试验表明,水声通信机的作用距离几乎覆盖了所有地球海洋的深度,7s或14s传输一幅光图或声图。      

无精准同步的小规模水声网络节点相对自定位

提出了一种无精准同步的小规模水声网络节点相对自定位方法。针对节点数量较少的小规模水声网络,利用水声通信在无精准时钟同步的情况下进行节点间测距,进而根据由相邻节点构成的三角形结构校正节点的相对位置。通过仿真得到,在几种典型拓扑结构下,该方法在测距误差不超过10 m时,将初始定位误差降低40%以上。在水声网络自组织的同时进行节点自定位,避免了传统的二次定位过程,节省了节点能耗和定位时间,并在一定范围内提高了定位精度。      

水下材料声学性能宽频段测量方法

本文根据脉冲法和传递函数法的测试原理,建立水下声学材料吸声性能宽频段测量方法,在同一水声声管,相同状态下,对橡胶材料吸声性能进行测试分析。分析表明:常压及加压环境下,采用传递函数法和脉冲法测量材料的吸声性能,在重合频段(4 kHz～5.5 kHz)测试结果基本一致,测试偏差小于5%,从而验证了不同测量原理,测试材料水下声学性能的通用性。因此,采用传递函数法和脉冲法,可以实现水下材料声学性能宽频带测试。     

Linearized iterative method for determining effects of vessel attitude error on single-beacon localization

Single-beacon localization is an advanced (and relatively new) acoustic localization technique. The traditional single-beacon uses non-linear trajectories to localize underwater vessels, which has notable drawbacks in actual underwater operations. To mitigate the limitations associated with non-linear trajectories, we developed an innovative single-beacon localization with linear trajectories. The traditional linearized least square method is not suited to linear trajectories, so we developed a linearized iterative method that includes a virtual long baseline array to analyze the effects of vessel attitude error on single-beacon localization results. We simulated the forward velocity, number of beacons, distance measurement period, and vessel heading impact on horizontal localization. The results showed that according to the proposed analysis method, localization precision is strongly dependent on vessel attitude error.     

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。      

混响声场条件下水声互易传递函数的测量及应用

对不规则的混响声场情况的互易测量方法进行了理论研究,对相关测量误差提出了修正方法。通过测量结果的空间平均和混响环境对声能密度影响的评估,修正了声源体积速度的计算值,并在水中进行了试验验证。经修正后的互易测量结果与正向实测结果基本一致。表明混响声场不影响互易原理有效性的成立,但影响了声源体积速度的计算,进而影响了应用互易原理对传递函数的测量。提出的修正方法在不规则的混响声场情况下简单有效,结论为今后基于互易原理的工程应用提供了参考和依据。