High Frequency Sonar Research Articles

Optimizing hydrophone-preamplifier systems: Theoretical design, computational analysis, and experimental validation for towed array applications

Hydrophone response parameters greatly influence the design of pre-amplifier and analog to digital conversion (ADC) components. Here, we show a comprehensive methodology for the modeling of hydrophone response, focusing on the theoretical, computational, and experimental approach for low and high frequency SONAR applications. Theoretical calculation of hydrophone response based on electromechanical properties is compared with Finite Element Analysis (FEA) and experimental measurement. An electrical equivalent hydrophone simulator Butterworth-Van Dyke (BVD) circuit is constructed based on admittance and susceptance measurements to represent the transducer's electrical behavior for testing pre-amplifier and ADC response without the presence of environmental or hydrophone noise. This model facilitates a systematic approach to towed array front-end design with hardware in the loop to update models to improve performance prediction. Measurements of the constructed transducer system validate the theoretical and computational models, providing insights into real-world performance.

Recognition of Object Presence and Material Type in a Water Container Using High Frequency Ultrasound

Detection and characterization of soluble, diffuse, and solid objects and their characteristics in water has important implications in various applications, including water quality assessment and incontinence monitoring for health applications. In particular in the latter task, it is essential to be able to non-intrusively detect the appearance, presence, and consistency of materials in the water without the need for special purpose instruments or a special purpose setting. To achieve this, this work investigates the potential use of high frequency sonar sensors retrofitted to an existing, water-filled container to detect and characterize events where materials are added to the water, and to classify characteristics of the materials in terms of solubility, granularity, and density.

The Preliminary Study on Backscattering Strength of High Frequency Sonar in Extremely Shallow Water

The nearshore water area is a very important part of maritime safety and application water area. Due to the complexity of sound propagation, and the influence of terrain, geology, tidal range and experiment’s difficulty, there has few researches in this area. Based on an existing engineering works, this article attempts to give some related calculations of the bistatic backscattered acoustic strength received and launched by a high frequency sonar in the extremely shallow water area with the depth less than 10 meters, and followed by in situ experiments test. It shows that the calculated results are in good agreement with the experimental tests. This work is a preliminary attempt in the study of extremely shallow water areas, and will provide a certain reference for the later sonar work in extremely shallow water areas.

Assessing effectiveness and side effects of likely “seal safe” pinger sounds to ward off endangered franciscana dolphins (Pontoporia blainvillei)

AbstractThe franciscana (Pontoporia blainvillei) is the most endangered dolphin in the western South Atlantic Ocean due to bycatch. Our goal was to test the efficiency of a likely “seal safe” pinger (Banana Pinger, Fishtek Marine Ltd.) to ward off franciscanas, as well as investigating possible side effects of habituation and habitat exclusion. We deployed the pinger within a grid of click detectors (C‐POD, Chelonia Ltd.) in Babitonga Bay, southern Brazil, and the narrow band high frequency sonar click trains were used as a proxy for presence of the franciscanas and response to the pinger. The presence of franciscanas next to the pinger and at 100 m away decreased by 19.4% and 15.4%, respectively, when the pinger was switched on, indicating that the franciscanas avoided the area of the pinger. This avoidance response could not be seen at 400 m away. No habituation effect was noted at any distance. There was a slight gradual decrease in detections over the course of the study at all distances, which is probably related to seasonal variation in the population's habitat use, but this requires attention in future studies. The likely “seal safe” pinger sounds effectively warded off franciscanas and thus has the potential to reduce bycatch.

Sparse Reconstruction-Based Inverse Scattering Imaging in a Shallow Water Environment

Bistatic sonar or multistatic sonar system can collect more scattering information of targets than a monostatic sonar system. In this paper, sparse learning via iterative minimization method (SLIM) is introduced to distinguish wave components for time-domain (TD) back-propagation (BP) inverse scattering imaging improvement. Unlike the prevailing high central frequency (>100 kHz) and wideband imaging sonar systems, a relatively low-frequency band (1–10 kHz) is considered here. Due to the low sidelobe output of SLIM, the investigated object’s surface in TD-BP image is much clearer in an ideal two-dimensional free field case. Furthermore, when the environmental information is known, this sparse reconstruction-based channel deconvolution method can be implemented to recognize, categorize the main propagating paths and then rectify their time of arrivals. Compared with the phase conjugation-based channel deconvolution method, the proposed approach’s results have fewer sidelobes and higher signal-to-background ratio in the simulation.

Local suppression of bioturbation and its acoustic consequences

Seafloor roughness in shallow waters can be both spatially and temporally dynamic. While wind-driven waves and bottom currents can generate bedforms such as ripples on sand sediments, bottom-feeding fish tend to limit the lifetime of these anisotropic features. This greatly reduces the time during which high frequency sonars can exploit the ripples to coherently penetrate the sediment at subcritical angles. Sonar performance prediction in these environments therefore relies heavily on sediment transport models to generate roughness predictions that accurately reflect changes on these time scales. The competition between the hydrodynamics and biology of the environment can be further complicated by the natural introduction of materials which can locally suppress the bioturbation. Two examples are discussed here: The first comes from the Sediment Acoustics Experiment in 2004 where a storm deposited a layer of mud over some areas of seafloor protecting the bedforms from fish. The second is from the recent Target and Reverberation Experiment where there is evidence that spatially-varying shell content can also reduce the effects of bioturbation. The consequences for sonar performance in these two cases are discussed. [Work supported by the U.S. Office of Naval Research and the Strategic Environmental Research and Development Program.]

Acoustic Observation of Zooplankton Using High Frequency Sonar (Observasi Akustik Zooplankton Menggunakan Sonar Frekuensi Tinggi)

Underwater acoustic sampling techniques provide an advantage over traditional net-sampling for zooplankton research. The research presents a methodology for extracting both biological and physical information from high frequency sonar. These methods can easily provide the information that will improve our understanding of the spatial and temporal distribution of zooplankton. Measured acoustic data converted into biological organisms and numerical physics-based scattering models were used in this research. The numerical backscattering process was modeled using the Distorted-Wave Born Approximation (DWBA) to predict the amount of sound scattered by a weakly scattering animal. Both acoustic measurement and DWBA modeled scattering patterns showed that acoustic scattering levels are highly dependent on zooplankton orientation. The acoustic backscattering from zooplankton depends on the material properties (i.e. the sound speed and density of the zooplankton), the shape and size, and the orientation relative to the incident acoustic wave. DWBA model significantly improve the accuracy and precision of zooplankton acoustic surveys. Zooplankton data measurement and DWBA model analysis provide a basis for future acoustical studies.

Statistics of very high frequency sound scattered from wind-driven waves

The amplitude, Doppler spread, and temporal coherence of VHF scattering is important for the performance of high frequency sonars and underwater communications systems in operating scenarios where energy from the sea surface cannot be screened. For this talk, the amplitude and arrival time statistics of very high frequency (50 kHz–2000 kHz) sound scattered from a rough wind-driven wave surface are modeled. Saturation occurs in the normalized second moment of acoustic intensity when the surface correlation length exceeds a Fresnel zone length. Fluctuations in arrival time do not saturate and increase proportionally to the dominant surface wave component. Data collected at 300 kHz agree with the model results. Energy is first detected in the wind-driven surface wave field at wavelengths of 1.7 cm and 3.4 cm. The former wave corresponds to a gravity-capillary wave whose phase speed is at a minimum. The principal appearance of this type of wave has threshold implications for the range of acoustic transmission frequencies susceptible to saturation in amplitude statistics.

Fe Doped Hard PZT Ceramics for High Power SONAR Transducers

Fe doped lead zirconate titanate (PZT) ceramics are prepared by mixed-oxide route. The X-ray diffraction analysis confirms the phase formation of PZT perovskite structure. The dielectric constant and loss of the material are investigated by varying the sintering temperature and found to be 1020 and 0.002 respectively. The mechanical quality factor and piezoelectric charge coefficient for Fe doped PZT material are found to be 980 and 225 pC/N respectively. The grain size of the material is studied by using Scanning electron microscopy. These materials are used as flextensional transducers for high power low frequency SONAR applications.

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.

Testing of an extended target for use in high frequency sonar calibration

Acoustic backscatter tests were performed in a tank with a 200-kHz, 7°, SIMRAD EK60 Split-Beam Echo-Sounder, and a 256-beam RESON SeaBat 7125 Multi-Beam Echo-sounder. Tests were done in order to investigate the angular and range dependency of the scattering strength of a new test target in order to validate its use in sonar testing. This target was constructed of small chain links arranged in a “curtain” simulating an extended scattering surface, such as the seafloor. Target strength for individual links was collected as the links were rotated 360°. The links are combined into an extended surface target, spacing between scatterers being approximately 1 cm. The scattering network irregularity is enough to ensure random phase at the wavelength considered. The target scattering strength was measured as a function of grazing angle and range, hence varying the number of scatterers within the beam footprint. These tests suggest that the amplitude envelope of the scattered signals is Rayleigh distributed and that the backscatter strength depends linearly on the number of active scatterers, all desirable features for calibrating sonars used to make measurements of similarly random surfaces such as the seafloor. Results show a promising in-tank calibration technique when extended surface targets are desirable.

Echolocation by the harbour porpoise: life in coastal waters

The harbor porpoise is one of the smallest and most widely spread of all toothed whales. They are found abundantly in coastal waters all around the northern hemisphere. They are among the 11 species known to use high frequency sonar of relative narrow bandwidth. Their narrow biosonar beam helps isolate echoes from prey among those from unwanted items and noise. Obtaining echoes from small objects like net mesh, net floats, and small prey is facilitated by the very high peak frequency around 130 kHz with a wavelength of about 12 mm. We argue that such echolocation signals and narrow band auditory filters give the harbor porpoise a selective advantage in a coastal environment. Predation by killer whales and a minimum noise region in the ocean around 130 kHz may have provided selection pressures for using narrow bandwidth high frequency biosonar signals.

Application of low‐frequency methods for estimating object size.

Classification of submerged objects has traditionally been performed using high frequency sonars and imaging techniques. While this permits fine matching of target templates to images acquired in the field, HF methods are necessarily limited in range due to absorption of sound by the water. LF sonars, while offering increased detection range, come with some significant challenges related to the limited bandwidth available. Nonetheless, we show that it is feasible to estimate object size using nonimaging techniques. There are a number of low‐frequency phenomena that can be exploited to this end. Among these are edge diffraction in which sharply angled facets of objects (“edges”) act like independent, radiating point sources, and helical waves, which can be set up in cylindrical objects. We show that with appropriate postprocessing of these returns, object edges can be localized thus allowing object extent to be assessed. In this paper, we describe our processing system, and then give results when this system is applied to over 40 sequences of returns from a rail system. In each sequence, a single solid, proud cylinder is insonified, and our system reports an estimate of cylinder length and radius. Histograms of these estimates cluster roughly around the true values.

A new calculation method for the number of radial slots of a Terfenol rod

Terfenol is an ideal choice for medium to high power low frequency sonar. It can offer the transducer designer higher strain, higher power density, but the designer must be aware of the eddy current. To enhance efficiency of the barrel-stave transducer powered by a Terfenol rod, radial slots rather than laminations were used to control eddy currents in the Terfenol drive rod, and the effectiveness and the number of these slots were studied experimentally and calculated by finite element modeling. Based on the characteristic of vortex path,a new simple geometrical method to calculate the number of the radial slots of a Terfenol rod at the operating frequency is put forward in this paper. Moreover, the calculated results are in good agreement with those of using the finite element method (FEM) for the slotted Terfenol rod given by the literature. The method will save much cost to design Terfenol rod transducers.

When echolocating bats do not echolocate

Echolocating bats are known to continuously generate high frequency sonar pulses and listen to the reflecting echoes to localize objects and orient in the environment. However, silent behavior has been reported in a recent paper, which demonstrated that the big brown bat (Eptesicus fuscus) can fly a relative long distant (0.6 to 8 m) without echolocating when flying with another conspecific in a large flight room.1 Methodology and conclusion developed in this study have the potential for further experimental design to answer the question of how millions of bats navigate and orient in cohesive groups. In addition, the discovery of silent behavior suggests the possible use of cooperative sonar in echolocating animals.

Acoustic signal processing methods for detecting intrusions and threats in the battlespace

The processing of acoustic sensor data enables the detection, classification, localization and tracking of intrusions and threats in the battlespace. Initially, passive acoustic signal processing methods that are used in unattended ground sensor networks and onboard uninhabited aerial vehicles are reviewed. These methods process radiated noise (acoustic signature) data generated by sources of military interest and extract tactical information on air and ground vehicles as well as direct (rifle) and indirect (artillery/mortar) fire weapons. Examples of applying various passive acoustic signal processing methods to real sensor data collected during field experiments are presented. The tactical parameter estimates derived from these acoustic methods are then compared with ground truth data. Next, the application of active sonar signal processing to the automatic detection and tracking of a fast inshore watercraft in a cluttered harbor environment is demonstrated using real data. The air bubbles associated with wakes from high‐speed surface craft are highly reflective of incident high frequency sonar signal transmissions. Finally, various high frequency active sonar methods that use both real and synthetic apertures to image sea mines are reviewed and demonstrated.

A comparison of hydrophone near-field scans and optical techniques for characterising high frequency sonar transducers

Two potential methods of fully characterising the response of high frequency sonar transducers and arrays operating in the frequency range 100 kHz to 500 kHz are compared. In the first approach two-dimensional planar scans, with a spatial resolution of better than half a wavelength, are performed in the acoustic near-field using a small probe hydrophone. The measured two-dimensional data are propagated numerically using a Fourier Transform method to predict the far-field response. Alternatively the data can be back-propagated to re-construct the pressure distribution at the source, a powerful diagnostic technique which can identify defects in transducers and array elements. The second approach uses a scanning laser vibrometer to measure the velocity of the transducer surface; with the resulting velocity data also being used to predict the far-field response by numerical propagation. The two approaches are compared for a number of devices. Comparison of the propagated hydrophone near-field scan data with direct measurements at these ranges shows very good agreement, indicating the usefulness of the method for deriving far-field transducer responses from near-field measurements in laboratory tanks. The potential limitations introduced to the optical approach by the acousto-optic effect are discussed.

Neural network-based underwater image classification for Autonomous Underwater Vehicles

Image processing has been one of hot issues for real world robot applications such as navigation and visual servoing. In case of underwater robot application, however, conventional optical camera-based images have many limitations for real application due to visibility in turbid water, image saturation under underwater light in the deep water, and short visible range in the water. Thus, most of underwater image applications use high frequency sonar to get precise acoustic image. There have been some approaches to apply optical image processing methods to acoustic image, but performance is still not good enough for automatic classification/recognition. In this paper, a neural network-based image processing algorithm is proposed for acoustic image classification. Especially, shadow of an acoustic object is mainly used as a cue of the classification. The neural network classifies a pre-taught image from noisy and/or occlude object images. In order to get fast learning and retrieving, a Bidirectional Associative Memory (BAM) is used. It is remarked that the BAM doesn't need many learning trials, but just simple multiplication of two vectors for generating a correlation matrix. However, because of the simple calculation, it is not guaranteed to learn and recall all data set. Thus, it is needed to modify the BAM for improving its performance. In this paper, complement data set and weighted learning factor are used to improve the BAM performance. The test results show that the proposed method successfully classified 4 pre-taught object images from various underwater object images with up to 50% of B/W noise.

Acoustic Visualization of Nonlinear Internal Gravity Waves Using an Improved High Frequency Sonar System

High frequency sonar systems have been used by the Naval Research Laboratory to study nonlinear internal gravity waves and define the fine structure of ocean temperature and salinity layers that are found in coastal waters, usually within 130 meters of the surface. Of particular interest is the fine structure of these waves, which are being investigated using high sensitivity sonar systems that provide 1 m horizontal resolution and less than 8 cm vertical resolution. This article describes the integration of commercial and custom-designed components, including a recently patented transmitter-receiver switch. The significance of this T-R switch is that it improves the sensitivity of short-range sonar systems, enables a more refined measurement of nonlinear internal gravity waves, and could have broad industry applications.

Überwachung von Bauteilen im Wasser unter Berücksichtigung gültiger Normen

In Part 2 methodologies for building monitoring with the high frequency sonar MS 1000 are described. On the basis of practical examples (scans of piers and pillars in the rivers Danube and Mur) the possibilities and borders of the detection of damages by means of high resolution sonars are pointed out.