Sonar Signal Research Articles

CutFM sonar signal design

Sonar-based underwater surveillance, including the problem of diver detection, is a challenging task. Particularly in reverberation limited environments like harbors and coastal waters, it is usually essential to utilize the Doppler effect caused by the target movement, in order to separate the diver from the quasi-stationary background. The common choice for Doppler processing systems is to use the continuous wave (CW) signal or one of its modifications. However, it is known that the CW waveform provides poor range resolution. In this paper a frequency modulation (FM) based Doppler selective signal, called cutFM, is introduced. The cutFM signal is characterized by a comparable Doppler resolution as that of the CW signal, but with improved range resolution. The paper provides Doppler processing gain estimates and the theoretical predictions concerning cutFM are supported by measurement results.

A Real-Time 3-D Underwater Acoustical Imaging System

Real-time 3-D acoustical imaging technique is a key advance to broaden the scope and enhance the feasibility of underwater missions. In this paper, a real-time 3-D underwater acoustical imaging system to handle the actual tasks under a narrowband excitation is presented. The system consists of three parts: a transmitter, a receiving hydrophone array, and a signal processor. In this system, a distributed and parallel subarray (DPS) beamforming algorithm is proposed to process the acquired signals from a scene placed in the far field. The DPS beamforming algorithm is an approximate method for the sonar signal processing with an advantageous computational efficiency. The direct method (DM) and fast Fourier transform (FFT) beamforming are compared with DPS beamforming for the memory and computational requirements. Based on this algorithm, a prototype was developed, which has been extensively employed in the lake and sea trials. The trials demonstrate that the system can achieve the 3-D imaging of the scene and meet the real-time requirement of the underwater operations.

Adaptive noise cancelling and time–frequency techniques for rail surface defect detection

Adaptive noise cancelling (ANC) is a technique which is very effective to remove additive noises from the contaminated signals. It has been widely used in the fields of telecommunication, radar and sonar signal processing. However it was seldom used for the surveillance and diagnosis of mechanical systems before late of 1990s. As a promising technique it has gradually been exploited for the purpose of condition monitoring and fault diagnosis. Time–frequency analysis is another useful tool for condition monitoring and fault diagnosis purpose as time–frequency analysis can keep both time and frequency information simultaneously. This paper presents an ANC and time–frequency application for railway wheel flat and rail surface defect detection. The experimental results from a scaled roller test rig show that this approach can significantly reduce unwanted interferences and extract the weak signals from strong background noises. The combination of ANC and time–frequency analysis may provide us one of useful tools for condition monitoring and fault diagnosis of railway vehicles.

Effect of Series of 1 to 2 kHz and 6 to 7 kHz Up-Sweeps and Down-Sweeps on the Behavior of a Harbor Porpoise (Phocoena phocoena)

To compare the effect of naval sonar up-sweeps and down-sweeps on the behavior of harbor porpoises, a harbor porpoise in a large pool was exposed to simulated low- and mid-frequency active sonar signals (series of 1-s duration frequency-modulated sweeps). Three sweep pairs were tested: (1) a 1 to 2 kHz up-sweep was compared with a 2 to 1 kHz down-sweep (both without harmonics) at a mean received sound pressure level (mean received SPL) of 114 dB re 1 µPa; (2) a 1 to 2 kHz up-sweep was compared with a 2 to 1 kHz downsweep (both with harmonics; mean received SPL: 123 dB re 1 µPa); and (3) a 6 to 7 kHz up-sweep was compared with a 7 to 6 kHz down-sweep (both without harmonics; mean SPL: 107 dB re 1 µPa). For each sweep pair, the level was chosen during a pretest session with the intention that the harbor porpoise would respond to the sounds by moving away from the projector and surfacing more often (i.e., he would show a change in behavior). The study consists of three separate parts, so only a comparison within sweep pairs could be made and not between sweep pairs. For the 1 to 2 kHz sweeps with harmonics, the harbor porpoise swam further away from the sound source in response to the up-sweeps than to the downsweeps. For the other two sweep pairs, sweep type (up-sweep or down-sweep) caused no significant difference in the harbor porpoise’s response. Thus, to allow the evaluation of potential effects of sonar sounds on harbor porpoises, sonar signal measurements should include the harmonics. For simulated naval sonar sounds with fundamental frequencies in the 1 to 2 kHz range containing harmonics, using down-sweeps appears to affect harbor porpoise behavior less than using up-sweeps.

삼중 버퍼링 방법을 이용한 실시간 소나 신호 디스플레이를 위한 FPGA 임베디드 시스템의 구현

The CRT monitor display system for SONAR signal that are commonly used in ships or naval vessels uses vector scanning method. Therefore the processing circuits of the system are complex. Also the purchase of parts is difficult as well as high-cost because the production had been shut down. FPGA-based embedded system is flexible to various digital applications because it can be able to simplify processing circuits and to make a easy customized design for end user, and it provides low-cost high-speed performance. In this paper, we describe an implementation of FPGA embedded system for real-time SONAR signal display using the triple buffering method to overcome some weakness of existing CRT system. Our system provides real-time acquisition and display capability of SONAR signal, and removes afterimage effect that is a critical problem of the system proposed in the preceding study.

A Dual-DSP Sonobuoy Signal Processing System

Sonobuoy is used as aviation antisubmarine device to detect submarines, and its wireless communication mechanism would introduce radio interference. The speech signal needs to be identified from the submarine noise in order to facilitate sonar signal processing system to do further processing of the signal. This paper presents a TS-201 based dual-DSP sonobuoy signal processing system, and proposes an algorithm using Cubic Spline Interpolation and Pearson correlation coefficient to identify the speech signal from submarine radiated noise signal. This article describes the specific signal processing algorithm of the system, the hardware and software design of the system. This article uses a large number of data from experiments to test the hardware and software systems separately. The results of tests are analyzed, which indicate that the system function well in identifying speech signal from submarine radiated noise signal to, with a percentage of 98% correct rate.

High-resolution habitat mapping on mud fields: New approach to quantitative mapping of Ocean quahog

During 2009–2012 stocks of the bivalve Arctica islandica (Linnaeus, 1767) (Ocean quahog) in Kandalaksha Bay (the White Sea) has been assessed using a side-scan sonar, grab sampling and underwater photo imaging.Structurally uniform localities were highlighted on the basis of side-scan signal. Each type of a signal reflects combination of sediment type, microtopography and structural characteristics of benthic community. The distribution of A. islandica was the predominant factor in determining community structure. Seabed attributes considered most significant were defined for each type of substrate type. Relations of sonar signal and sediment type were used for landscape mapping based on sonar data. Community characteristics at known localities were reliably interpolated to the area of survey using statistical processing of geophysical data.A method of integrated sonar and sampling data interpretation for high-resolution mapping of A. islandica by biomass groups, benthic faunal groups and associated habitats was developed.

Underwater Sonar Signals Recognition by Incremental Data Stream Mining with Conflict Analysis

Sonar signals recognition is an important task in detecting the presence of some significant objects under the sea. In military, sonar signals are used in lieu of visuals to navigate underwater and/or locate enemy submarines in proximity. In particular, classification algorithm in data mining has been applied in sonar signal recognition for recognizing the type of surfaces from which the sonar waves are bounced. Classification algorithms in traditional data mining approach offer fair accuracy by training a classification model with the full dataset, in batches. It is well known that sonar signals are continuous and they are collected as data streams. Although the earlier classification algorithms are effective in traditional batch training, it may not be practical for incremental classifier learning. Since sonar signal data streams can amount to infinity, the data preprocessing time must be kept to a minimum to fulfill the need for high speed. This paper presents an alternative data mining strategy suitable for the progressive purging of noisy data via fast conflict analysis from the data stream without the need to learn from the whole dataset at one time. Simulation experiments are conducted and superior results are observed in supporting the efficacy of the methodology.

Adaptive Range-Doppler Imaging and Target Parameter Estimation in Multistatic Active Sonar Systems

Multistatic active sonar systems involve the transmission and reception of multiple probing sequences. Since the multiple simultaneously transmitted probing sequences act as interferences to one another, adaptive receiver filters are needed for interference suppression and for target range-Doppler imaging. Two adaptive receiver designs, namely, the iterative adaptive approach (IAA) and the sparse learning via iterative minimization (SLIM) method, are considered for range-Doppler imaging via multistatic active sonar. The so-obtained range-Doppler images allow us to further estimate the target parameters. Specifically, we use the popular quasi-Newton method for target position estimation and the least squares (LS) fitting approach for target velocity determination. The effectiveness of the proposed multistatic active sonar signal processing techniques is verified using numerical examples.

Leveraging spatial diversity to mitigate interference in underwater acoustic communication networks

Many acoustic channels suffer from interference which is neither narrowband nor impulsive. This relatively long duration partial band interference can be particularly detrimental to system performance. We survey recent work in interference mitigation and orthogonal frequency division multiplexing (OFDM) as background motivation to develop a spatial diversity receiver for use in underwater networks. The network consists of multiple distributed cabled hydrophones that receive data transmitted over a time-varying multipath channel in the presence of partial band interference produced by interfering active sonar signals as well as marine mammal vocalizations. In operational networks, many dropped messages are lost due to partial band interference which corrupts different portions of the received signal depending on the relative position of the interferers, information source and receivers due to the slow speed of propagation.

Analysis of Signals Under Compositional Noise With Applications to SONAR Data

In this paper, we consider the problem of denoising and classification of SONAR signals observed under compositional noise, i.e., they have been warped randomly along the x-axis. The traditional techniques do not account for such noise and, consequently, cannot provide a robust classification of signals. We apply a recent framework that: 1) uses a distance-based objective function for data alignment and noise reduction; and 2) leads to warping-invariant distances between signals for robust clustering and classification. We use this framework to introduce two distances that can be used for signal classification: a) a y-distance, which is the distance between the aligned signals; and b) an x-distance that measures the amount of warping needed to align the signals. We focus on the task of clustering and classifying objects, using acoustic spectrum (acoustic color), which is complicated by the uncertainties in aspect angles at data collections. Small changes in the aspect angles corrupt signals in a way that amounts to compositional noise. We demonstrate the use of the developed metrics in classification of acoustic color data and highlight improvements in signal classification over current methods.

Target phase information for acoustic target identification: Method and preliminary results

Target phase information in acoustic backscattering has been proposed as an additional target identification parameter. In general, incorporating phase into sonar signal processing for acoustical oceanography could aid in the assessment of fish populations and ecosystems. In this work, a broadband sonar system calibrated in amplitude and phase is used to measure the response of submerged targets in a laboratory water tank. Frequency domain data processing is applied, with target phase measured as a phase angle difference between two frequency components. This approach aims to eliminate range factors, leaving only target-induced phase features. The method is developed and validated by comparing experimental results to analytical and numerical methods, in the characterization of some targets with regular geometries such as spheres, shells, and cylinders. A compensation algorithm is implemented to account for phase ambiguities and arrive to a figure of merit for template classification. Simplified scenarios are studied in order to demonstrate the potential applicability of this method.

Dose-response relationships for the onset of avoidance of sonar by free-ranging killer whales.

Eight experimentally controlled exposures to 1-2 kHz or 6-7 kHz sonar signals were conducted with four killer whale groups. The source level and proximity of the source were increased during each exposure in order to reveal response thresholds. Detailed inspection of movements during each exposure session revealed sustained changes in speed and travel direction judged to be avoidance responses during six of eight sessions. Following methods developed for Phase-I clinical trials in human medicine, response thresholds ranging from 94 to 164 dB re 1 μPa received sound pressure level (SPL) were fitted to Bayesian dose-response functions. Thresholds did not consistently differ by sonar frequency or whether a group had previously been exposed, with a mean SPL response threshold of 142 ± 15 dB (mean ± s.d.). High levels of between- and within-individual variability were identified, indicating that thresholds depended upon other undefined contextual variables. The dose-response functions indicate that some killer whales started to avoid sonar at received SPL below thresholds assumed by the U.S. Navy. The predicted extent of habitat over which avoidance reactions occur depends upon whether whales responded to proximity or received SPL of the sonar or both, but was large enough to raise concerns about biological consequences to the whales.

Vocal matching of naval sonar signals by long‐finned pilot whales (Globicephala melas)

Alves, Ana; Antunes, Ricardo; Bird, Anna; Tyack, Peter L.; Miller, Patrick James O'Malley; Lam, Frans-Peter A.; Kvadsheim, Petter Helgevold. Vocal matching of naval sonar signals by long-finned pilot whales (Globicephala melas). Marine mammal science 2014 ;Volum 30.(3) s. 1248-1257

Behavioral responses by grey seals (Halichoerus grypus) to high frequency sonar

The use of high frequency sonar is now commonplace in the marine environment. Most marine mammals rely on sound to navigate, and for detecting prey, and there is the potential that the acoustic signals of sonar could cause behavioral responses. To investigate this, we carried out behavioral response tests with grey seals to two sonar systems (200 and 375kHz systems). Results showed that both systems had significant effects on the seals behavior; when the 200kHz sonar was active, seals spent significantly more time hauled out and, although seals remained swimming during operation of the 375kHz sonar, they were distributed further from the sonar. The results show that although peak sonar frequencies may be above marine mammal hearing ranges, high levels of sound can be produced within their hearing ranges that elicit behavioral responses; this has clear implications for the widespread use of sonar in the marine environment.

Approximation of a Warship Passive Sonar Signal Using Taylor Expansion

함정의 수동소나는 여러 개의 지향성과 무지향성 센서로 구성되어 있다. 함정 소나에 수신되는 음향 신호를 모의할 때, 일반적으로 임의의 소음원으로부터 소나에 장착된 모든 센서간의 음파 전달 모델링이 필요하다. 그러나 모든 센서에 대한 통합적인 계산은 시간이 많이 소모되며 소나 시뮬레이터의 성능을 저하시킨다. 본 연구에서는 음선 정보가 알려진 기준 센서가 존재한다고 할 때 그에 인접한 센서 위치에서의 소나 신호를 추정하는 근사적인 방법을 제안한다. 이 방법은 음선의 도달 시간에 대한 테일러 급수를 이용하여 개발되었으며 소나 개구면에 대한 Fraunhofer와 Fresnel 근사와 유사하다. 제안된 기법을 검증하기 위해 수동 소나에 대해 여러 수치실험이 수행되었다. 2차 항까지 테일러 근사를 적용한 근사법이 보다 우수한 결과를 보였다. 추가적으로 각각의 근사 해에 대한 오차 한계가 제시되었다. A passive sonar of warship is composed of several directional or omni-directional sensors. In order to model the acoustic signal received into a warship sonar, the wave propagation modeling is usually required from arbitrary noise source to all sensors equipped to the sonar. However, the full calculation for all sensors is time-consuming and the performance of sonar simulator deteriorates. In this study, we suggest an asymptotic method to estimate the sonar signal arrived to sensors adjacent to the reference sensor, where it is assumed that all information of eigenrays is known. This method is developed using Taylor series for the time delay of eigenray and similar to Fraunhofer and Fresnel approximation for sonar aperture. To validate the proposed method, some numerical experiments are performed for the passive sonar. The approximation when the second-order term is kept is vastly superior. In addition, the error criterion for each approximation is provided with a practical example.

Design of multistatic sonar space-time code detection signal and time reversal copy-correlation detection technology

A space-time code (STC) detection signal is designed for multistatic sonar to distinguish the multiple access echoes in the shallow water, and a time reversal (TR) copy-correlation detection method is presented for solving the problem of multi-path sub-channel differences when the vertical array is oblique. STC detection signal has a good orthogonality through modulating with pseudo-random signals, can distinguish multiple access target echoes while combating with sub-channel attenuation. The vertical array affected by current is oblique, its multi-path sub-channel differences causing signals from different sub-channels can not focus on the receiving end, so the array gain decreases. Meanwhile, it causes resolution to decline and the error rate of signal judgment to rise. Channel training signal is designed to estimate the sub-channel multipath environment, and the best matched detection signal for sub-channel differences is got through virtual time reversal mirror (VTRM) with the estimated channels and the received signal being detected by TR copy-correlation. Simulation results of tristatic sonar (two transmitters and one receiver) show that the SPC detection signal and TR copy-correlation can meet the requirements of multistatic sonar detection and distinguish the multiple access echoes in low SIR and complex channel environment. The best matched detection signal is got through VTRM (virtual time reversal mirror) with the estimated channels, and the received signal is detected by TR copy-correlation. Simulation results of tristatic sonar (two transmitters and one receiver) show that the STC detection signal and TR copy-correlation can meet the requirements of multistatic sonar detection and distinguish the multiple access echoes in low SIR environment.

Target Angular Position Classification with Synthesized Active Sonar Signals

Target Angular Position Classification with Synthesized Active Sonar Signals

Modeling and Experimental Verification of Echo Characteristics of 3 Dimensional Underwater Target

능동소나에 의한 표적 반향 신호는 다중경로 환경에서 전파됨에 따라 신호가 변형되어 수신된다. 또한 표적의 위치와 자세각에 따라 반향 신호 특성이 다르게 나타난다. 따라서 이러한 특성을 반영할 수 있는 3차원 형상의 표적 모델을 통해 반향 특성이 모의 되어야 한다. 본 논문에서는 3차원 표적신호의 모의를 위해 표적의 각 구성부를 형상 함수화 하였으며 각 구성부의 대표 반향점을 등간격으로 선정하여 표적 모델을 개발하였다. 개발된 표적 모델을 이용하여 음의 입사각에 따른 반향 신호와 표적강도(TS : Target Strength)를 모의하였다. 모의된 표적신호의 반향 강도 및 신호 특성을 검증하기 위해 조립이 가능한 구성부별 축소 모형을 제작하여 수조에서 축소 표적을 이용한 반향 실험을 수행하였다. When a active sonar signal is transmitted and returned back from a target, it has been distorted by various properties of acoustic channel such as multipath arrivals. And signals have been appeared to be different form by target position and attitude. Therefore, we simulated the target echo signal using 3 dimensional target model include reflects target features. In this paper, we develop components form of a simulated target model is made up equally spaced highlight points, and each part of the target consists of shape function. We can simulate a target echo signal and Target strength (TS) according to wave incident angle. To verify, we made small scale target in kit form and we had got underwater target signal for comparing simulation result in water tank.

LeID1. Time-frequency analysis: Theory and applications

Time-varying spectra are one of the most primitive sensations we experience, since we are surrounded by light of changing color, by sounds of varying pitch, and by many other phenomena whose periodicities change. The development of the physical and mathematical ideas needed to explain and understand time-varying spectra has evolved into the field now called “time-frequency analysis.” Among the many signals whose frequency content has been shown to vary in time are speech and other animal sounds, biomedical signals (e.g., heart sounds, heart rate, the electroencephalogram (EEG), the electromyogram (EMG), and others), music, radar and sonar signals, and machine vibrations, among others. In this tutorial, we give an overview of time-frequency analysis, with a focus on its applications. We describe how these methods impinge on and clarify issues in biomedical and biological signal analysis, wave propagation, random systems, non-linear systems, and other areas. Of particular interest is the application of time-frequency analysis to pulse propagation in dispersive media. We show that time-frequency considerations lead to new approximation methods for dynamic systems and wave propagation. We describe how to transform wave equations into phase-space, where the resulting equation is often more revealing than the original wave equation. We also discuss the applications to random systems and in particular to the propagation of noise fields.