Acoustic stereo images of the bottom surface

In order to enhance the efficiency of the interpretation of surface images obtained with a side scanning sonar, it is proposed to supplement the standard processing software with a program for obtaining acoustic stereo images. Examples of such images synthesized with this program using the data of a bottom sonar survey with a side scanning sonar and an echo sounder are presented. The cases are considered when the information on the bottom relief contained in sonar images obtained with a standard side scanning sonar or its modifications can be used instead of the data of an echo sounding survey.     

声相关海流剖面仪测速研究

声相关海流剖面仪(ACCP)适合深海测速,能够测得相对海底的绝对速度。文章在前人工作基础上,以声纳方程为基础,构造海底混响回波仿真模型,并对基于K irchhoff近似和利用微扰法的R ay le igh-R ice近似相结合的散射模型赋予新的物理意义,并将其应用到声相关测速仿真研究过程中,使仿真更加接近于海洋的实际环境。文章利用H ilbert变换进行包络检波来减小测速误差,并且根据接收信噪比得到了不同航速时能够达到最大底跟踪的距离,这与参考文献给出的结果是一致的。     

基于CAATI技术的条带测深/侧扫声纳系统C3D-LPM

侧扫声纳及多波束测深仪是应用非常广泛的海底地形地貌调查仪器。通过对侧扫声纳和多波束测深优缺点的对比分析,介绍了基于CAATI技术将高分辨率的侧扫图像和高质量的测深数据完美结合,生成高质量的三维图像的条带测深/侧扫声纳系统C3D-LPM,特别介绍了条带测深/侧扫声纳系统C3D-LPM的构造和技术规格。仪器实地使用结果表明,该仪器完全能够满足海洋工程和研究的需求,并具有其独特的技术特点和使用优势。     

A programmable microcomputer-based sonar echo processor for real-time processing

A programmable microcomputer-based sonar echo processor has been developed and field tested to process echo data in real time. The device was designed for use in fisheries acoustics and to analyze echoes from the sea floor. The instrument simultaneously performs the functions "echo integration" and "echo peak detection' on the sonar signal. The "echo integration" circuitry measures the relative acoustic energy of the echo while the "echo peak detection' electronics measure the probability density function (PDF) of the peak of the echo envelope. Each process is gated so the echoes may be processed in many short time intervals. In fisheries applications, estimates can be made of fish density (fish per unit volume), average backscattering cross section, and a combination of fish size and behavior. When using the device to analyze bottom echoes, it is possible to measure both the returned energy from the bottom sediment interfaces and the microrelief characteristics. The durability, flexibility, computer link, and floppy-disk data-storage features of the system are discussed. Data are presented of the processed echoes from biological organisms and the ocean bottom from a recent research cruise on the Atlantic Ocean near Cape Hatteras, NC. The biological results illustrated the organisms to be clearly divided into two separate spatial distributions-an observation not obvious from a standard echogram which was simultaneously used. The results from the bottom showed both 1) the difference in sub-bottom structure between two locations and 2) changes in microrelief of the water-bottom interface between another pair of locations.     

一种联合单波束测深的侧扫声呐海底线提取方法

论述了侧扫声呐的成像原理,针对目前常用侧扫声呐系统数据采集的相关特性,结合实际工程应用,提出了一种联合单波束测深的侧扫声呐海底线提取新方法,以便在数据后处理时进行快速准确地斜距改正。利用实测数据验证了该方法的有效性,并与成熟商用软件的提取结果和阈值法提取结果进行对比分析,结果表明该方法具有一定的可行性和优势。     

Enhanced Kalman Filter Algorithm Using the Invariance Principle

Target tracking in multistatic active sonar systems is often limited in shallow-water environments due to the high level of bottom reverberation that produces false detections. Past research has shown that these false alarms may be mitigated when complete knowledge of the environment is available for discrimination, but these methods are not robust to environmental uncertainty. Recent work has demonstrated the existence of a waveguide invariant for active sonar geometries. Since this parameter is independent of specifics of the environment, it may be used when the environment is poorly known. In this paper, the invariance extended Kalman filter (IEKF) is proposed as a new tracking algorithm that incorporates dynamic frequency information in the state vector and uses the invariance relation to improve tracker discrimination. IEKF performance is quantified with both simulated and experimental sonar data and results show that the IEKF tracks the target better than the conventional extended Kalman filter (CEKF) in the presence of false detections.      

General motion estimation from correlation sonar

The displacement of a sonar array can be estimated accurately using the correlation of bottom reverberation signals, at successive sweeps. This is the principle of the pulsed correlation log. In this paper, the conditions and accuracy of array horizontal translation estimation are analyzed. The case of a three-dimensional array is considered first, to show that in this case arbitrary translation and rotation can be estimated. The case of a plane array is then analyzed and it is shown that such an array allows estimation of horizontal translation. The derivation relies on modeling the space-time correlation function of bottom reverberation, which is assumed isotropic. Both directive and omnidirectional transmissions are considered. Accuracy of displacement estimates are derived, showing the influence of wavelength, grazing angle, bandwidth, number of overlapping hydrophones, and reverberation-to-noise ratio     

胜利埕岛海域海底松软沉积物声学探测方法探讨

胜利埕岛海域位于复杂的黄河三角洲沉积体系中．由于黄河的断流,在风浪和海流作用下原三角洲体系受到侵蚀．在部分海底具有松散沉积物沉积。采用侧扫声纳、双频测深仪及浅地层剖面仪3种海上物探方法,对埕岛海域海底松软沉积物进行声学探测,确定了浮泥、软土层顶、海底界面及浮泥和软土层和海底界面及浮泥和软土层的厚度,研究了埕岛海域海底松软沉积物的基本分布变化规律,为今后海洋工程地质勘察海底松软沉积物奠定了基础。     

一种多波束声呐回波信号时延的实时特征窗分析方法

本文介绍了一种多波束声呐回波信号时延的实时分析方法。通过实时提取信号的幅度及形状的综合特征计算出信号的时延。该方法具有较强的抗干扰能力,算法快速、准确,适合于多波束声呐系统的回波信号实时分析处理。     

Undersea Target Classification Using Canonical Correlation Analysis

Canonical correlation analysis is employed as a multiaspect feature extraction method for underwater target classification. The method exploits linear dependence or coherence between two consecutive sonar returns, at different aspect angles. This is accomplished by extracting the dominant canonical correlations between the two sonar returns and using them as features for classifying mine-like objects from nonmine-like objects. The experimental results on a wideband acoustic backscattered data set, which contains sonar returns from several mine-like and nonmine-like objects in two different environmental conditions, show the promise of canonical correlation features for mine-like versus nonmine-like discrimination. The results also reveal that in a fixed bottom condition, canonical correlation features are relatively invariant to changes in aspect angle.     

Technology for bottom relief and sedimentation surveys of White-Sea river estuaries

Experimental bottom relief survey technology and investigation results are presented. Investigations were conducted over about six years at several White-Sea river estuaries onboard the R/V Ecolog. Geomorphology data was obtained using an instrument complex that included an MKS, Microsound side scan sonar, AP-5 acoustic profiler, and LMS-350 echo sounder. ECHOGRAPH and WINRASTR original software was used for data gathering and processing.     

Two-way time spreading and path loss in shallow water at 20-40 kHz

Two-way time spreading and path-loss measurements were collected in water 100 m deep, off the coast of Nova Scotia. Data were collected at frequencies of 20-22 kHz, 27-29 kHz, and 35-37 kHz using linear FM pulses 0.160 s in duration. The source-receiver was an anchored, high-frequency active sonar, and the target was a free-drifting echo repeater. Sonar and target positions were recorded using a portable tracking range. In the paper, two-way time spreading and path loss measurements are compared with modeled estimates obtained using an enhanced version of the generic sonar model (GSM). The GSM estimates of time spreading due to multipath propagation compare favorably with the experimental data. The model indicates that the path loss for individual eigenrays was extremely sensitive to fluctuations in the sound-speed profile. This led to substantial variation in the model output depending on the choice of profile. In place of the model, an empirical estimate of path loss was computed from the data. We obtained a two-way spreading loss of 2[18.4log₁₀(R)] where R is the range from sonar to target. The data were also used to compute the standard deviation of the received echo intensity at each frequency. The standard deviation was computed two different ways. First it was computed using the peak echo level from each of the pulses at a given frequency. Then, it was computed from the total energy received from each of the pings. At all frequencies, the standard deviation was 1-2 dB lower when computed from the total received energy     

联合小波和NLM滤波的侧扫声纳回波信号降噪

为进一步降低侧扫声纳回波信号中非高斯分布的乘性噪声,获取更佳效果的侧扫声纳图像,提出了一种利用小波和NLM(nonlocal means)滤波的组合降噪方法.首先采用同态变换将侧扫声纳回波ping信号中的乘性噪声转换为加性噪声,然后利用小波阈值和NLM滤波对侧扫声纳每ping回波数据实施降噪处理,最后经过小波反变换和指...     

Measurement of seabed topography by multibeam sonar using CFFT

A precise ocean bottom map for ocean surveying and dredging is desired. Especially in dredging, it is essential to know the seabed topography in real time without being affected by scatterers (for example floating sand and mud) in the seawater during work. To meet these requirements, the multi-narrow-beam sonar system (MBSS) has been developed. The MBSS forms beams with the use of the complex fast Fourier transform (CFFT) algorithm. In the MBSS, arithmetic mean processing is employed to eliminate echo from scatterers and the measurement error due to the oblique incident angle is reduced by peak value detection processing. By using these processes, an ocean bottom map can be accurately obtained. It is both theoretically and experimentally shown that the distribution of echo intensity from scatterers is approximated by the Rayleigh probability density function. The arithmetic mean of four to eight successively received echoes from scatterers reduces the variance of the echo intensity distribution by 6 to 12 dB.     

Detection of objects on the sea bottom using backscatteringcharacteristics dependent on the observation point

Sector-scanning sonar systems image the sea bottom to detect objects that can be distinguished from the background structure of the sea bottom. In current systems, images are displayed and discarded as new image data become available, In this paper, a method for improving sonar detection by utilizing all images in a sequence is investigated. The proposed method requires that sonar data are acquired with a sector-scanning sonar in a side-looking configuration. It is demonstrated that these data can be used to detect observation-point-dependent changes in sea-bottom backscattering characteristics. These changes provide additional cues for discrimination that can improve the detection of objects on the sea bottom. Results of applying the method to experimental data are presented     

Design constraints and error analysis of the temporal correlationlog

The basic principles of spatial and of temporal correlation sonar for velocity measurement of both surface vessels and autonomous underwear vehicles are considered, showing the advantages of using a pulsed temporal correlation log. To achieve correlation, the conditions for waveform invariance must be met, and there is a velocity-depth limitation to be observed; these are described in detail. Practical design constraints such as the effects of different transducer sizes/geometry and carrier frequencies are also considered     

混浊水域多波束反向散射强度传播损失改正

为了改善现有的反向散射强度传播损失改正方法在混浊水域适应性较弱的问题,提出了混浊水域声传播损失计算模型。首先利用不同深度的海洋环境参数构建声波吸收系数剖面,然后基于声速,沿波束传播路径,对每个波束分层计算传播损失。实验分析表明,本方法传播损失改正效果最佳,其Spearman等级相关系数绝对值仅为0.04,远小于传统模型和TVG改正,大大减弱了混浊水域情况下多波束回波强度与传播距离的相关性,有效改善了多波束声呐图像的质量。     

多波束回波强度数据记录方式比较

分析了三种不同多波束测深系统回波强度的记录方式及数据结构,基于各自生成声纳图像的特点规律的差异,按其声纳图像不同用途对多波束测深系统进行了归类,其结果可为用户结合自身需求,正确购置多波束测深系统及合理应用声纳图像提供参考.     

Single-ping target speed and course estimation using a bistatic sonar

This paper focuses on estimating the two-dimensional (2-D) target-speed vector (course and speed) using a multistatic sonar that consists of one monostatic sonar and one bistatic receiver. The speed and course estimates are obtained after a single transmission. The theory on bistatic Doppler and 2-D target-speed vector estimation is first considered and then applied to simulated and real data. The results can be used to improve classification algorithms or to feed speed information to tracking algorithms, for example.