Underwater Acoustics

Scientific and technological development necessitates often legal regulation, to be achieved through an interaction between science and law during the decision-making process. Taking as an example the case of underwater noise pollution, the examination of which is underway in many international organisations with a view towards its regulation, the article proposes to comment upon some aspects of this interaction. It is finally submitted that law provides sufficient legal principles and institutionalised frameworks for cooperation, which however have not been sufficiently put in use so far.

A model of the multibeam echosounding process was developed. This model has now been used as the basis for the application of a model inversion technique, with the aim of analyzing midwater multibeam echosounder data, for fisheries applications.

Underwater wireless sensor networks (UWSN) consist of a certain number of sensors that interact to send the sensed data to the sink node and perform collaborative task. Most UWSN choose acoustic as a communication medium for wireless transmission. However, electromagnetic waves are also offer a great merit in special underwater environment such as shallow water. UWSN is significantly different from terrestrial sensor networks in many aspects such as mobility of sensor nodes due to water current, propagation delay and propagation loss. These distinctions feature of underwater sensor network pose many new challenges for delivering information from sensor nodes to sink node effectively in UWSN. To achieve reliable data transfer in underwater sensor network scenarios, a new event MAC protocol need to be developed to provide energy efficient and reliable upstream data transfer.

One of the major applications of underwater acoustic sensor networks (UWASN) is ocean environment monitoring. Employing data mules is an energy efficient way of data collection from the underwater sensor nodes in such a network. A data mule node such as an autonomous underwater vehicle (AUV) periodically visits the stationary nodes to download data. By conserving the power required for

Abstract: Vector sensors measure,both the acoustic pressure and the three components,of particle velocity. Because of this, a vector sensor array (VSA) has the advantage of being able to provide substantially higher directivity with a much,smaller aperture than an array of traditional scalar (pressure only) hydrophones. Although several, most of them theoretic, works were published from early nineties, only in the

Although the songs of humpback whales have been extensively studied, other vocalizations and percussive sounds, referred to as "social sounds," have received little attention. This study presents the social vocalization repertoire of migrating east Australian humpback whales from a sample of 660 sounds recorded from 61 groups of varying composition, over three years. The social vocalization repertoire of humpback whales was much larger than previously described with a total of 34 separate call types classified aurally and by spectrographic analysis as well as statistically. Of these, 21 call types were the same as units of the song current at the time of recording but used individually instead of as part of the song sequence, while the other 13 calls were stable over the three years of the study and were not part of the song. This study provides a catalog of sounds that can be used as a basis for future studies. It is an essential first step in determining the function, contextual use and cultural transmission of humpback social vocalizations.

Media Access Control (MAC) must be carefully considered in multi-hop Underwater Acoustic Sensor Networks (UASNs) due to limited bandwidth and large propagation delay. In particular, variable propagation delays in UASNs cause inaccurate time synchronization and therefore make reservation-based protocols less favorable. Large propagation delays limit the performance of carrier sense in predicting the status of the intended recipients, and therefore CSMA protocols show bad performance in UASNs too. Therefore, simple protocols, such as Aloha, show promise for UASNs. In this paper we consider the performance of a multi-hop ppersistent ALOHA protocol.

The purpose of this research is to investigate multipath arrival structures that are present in received passive sonar data and exploit this for enhanced passive sonar detection and tracking capability. OBJECTIVES Inherent in passive sonar systems are several challenges that any effective system implementation must address. One of these challenges is how to best treat multipath arrivals. In some cases these can be a hindrance while in this research they are exploited. In certain environments, multipath arrivals retain significant coherence with respect to each other. This fact has been noted and exploited in recent decades with the development of the class of techniques known as matched field processing (MFP). While there has been a significant amount of academic focus on developing this approach in the context of the more established array processing methodologies, its practical adoption has been hampered due to the need for accurate environmental models. Despite this shortfall, the conceptual basis of using multipath arrivals to enhance target localization still holds promise. In this project, the emphasis is on analytically and experimentally determining techniques to measure and utilize multipath. Recent studies into localization of marine mammals have shown that with only rough environmental models, 3-D localization is possible using a single hydrophone [Tiemann, 2006]. The principle of using multipath for range-depth localization is not new, however until recently the computational complexity of applying this to azimuth-dependent bathymetry has been prohibitive. Whale clicks are impulsive, so multipath structure is evident in raw time-domain data. However, this is not true of vessel noise, so this localization concept is extended to pulse compressed time-series data [See publication #1]. Recent advances in robotics, low power embedded computing, and sensor technologies (to name a few) have led to the advent of autonomous underwater vehicles (AUVs). Determining the best ways of designing passive sonar systems for these mobile platforms is an active area of research. In the GLASS'12 experiment performed by CMRE (with Portland State University collaborating), a hybrid (glider/propeller) AUV was outfitted with a compact nose-mounted hydrophone array consisting of tetrahedral and vertical line sub arrays. The small aperture, rigid frame, and high sample rate are

Techniques based on impulsive sources are used since the beginning of the Underwater Acoustic science, to evaluate the distance of objects and to plot the profile of the sea bottom. In this paper the authors investigate the behavior of three not-impulsive techniques for the measurement of impulse responses: MLS (Maximum Length Sequence) signal, linear sine sweep and logarithmic sine sweep. This work will focus the attention on advantages and defects of these tree different methods, in comparison with the traditional pulse-based sonar techniques. The mathematical theory for the generation of the MLS, sine sweep signals and for the deconvolution of the system's impulse response are first described. Then a software implementation of the measurement methods, based on the creation of plug-ins for a shareware waveform editor, running on a low cost PC is demonstrated. Some experiments conducted under controlled conditions and in the sea show that the proposed techniques produce images of the bottom profile with higher signal-to-noise ratio and better spatial resolution than those obtainable with the impulsive technique. Moreover signal-to-noise ratio increases using sine sweep signal instead of MLS one. The new techniques seem superior also for some practical aspects connected with their very nature, which make them almost inaudible and makes the sound source barely localizable: this is very important for military applications.

Acoustic transmission loss (TL) and supporting ocean environmental data collected during the Asian Seas International Acoustics Experiment (ASIAEX) on June 3, 2001, in the East China Sea (ECS), in a water depth of approximately 100 m are presented. Objectives of the data analysis are to explore the stochastic nature of TL in terms of the mean (TL) and the fluctuations around the mean (as described by the standard deviation (TL) and higher order statistics). In particular, we conjecture that TL robustly reflects the macrostate of the ocean, including the bottom, whereas uncertainties in TL as measured by TL are related to the microstate of the ocean, again including the bottom. Comparisons are made to TL data at a similar location, 200 km from the ASIAEX site, in waters of the same depth, by the Harsh Environment Program in September 1997. The TL is shown to be approximately horizontally isotropic with exception to a discrete anisotropic feature likely caused by internal waves. Various mechanisms of uncertainty are discussed to describe the microstate. These were not sufficiently resolved to identify the primary cause of variability.

The statistics of low-frequency, long-range acoustic transmissions in the North Pacific Ocean are presented. Broadband signals at center frequencies of 28, 75, and 84 Hz are analyzed at propagation ranges of 3252 to 5171 km, and transmissions were received on 700 and 1400 m long vertical receiver arrays with 35 m hydrophone spacing. In the analysis we focus on the energetic ''finale'' region of the broadband time front arrival pattern, where a multipath interference pattern exists. A Fourier analysis of 1 s regions in the finale provide narrowband data for examination as well. Two-dimensional ͑depth and time͒ phase unwrapping is employed to study separately the complex field phase and intensity. Because data sampling occured in 20 or 40 min intervals followed by long gaps, the acoustic fields are analyzed in terms of these 20 and 40 min and multiday observation times. An analysis of phase, intensity, and complex envelope variability as a function of depth and time is presented in terms of mean fields, variances, probability density functions ͑PDFs͒, covariance, spectra, and coherence. Observations are compared to a random multipath model of frequency and vertical wave number spectra for phase and log intensity, and the observations are compared to a broadband multipath model of scintillation index and coherence.

The long-term objective of this research is to develop a theoretical foundation for the design of new multi-static sonar concepts for littoral seabed imaging and mine counter measures (MCM) operations. Multistatic configurations have been made possible by the development with ONR support of new inexpensive autonomous underwater vehicle technology. OBJECTIVES The specific objective of this project is to develop and validate theoretical and numerical models of the 3-D spatial statistics of the seismo-acoustic field produced by targets on and within a rough elastic seabed. These models are then applied to develop an improved understanding of the dominant physical processes governing the performance of moderate-to-high frequency sonar systems for detection and classification of objects above and below the seabed in shallow water environments.

In the herring (Clupea harengus), the swim bladder is connected to both the alimentary canal and the anal opening. The anterior duct is used for filling the swim bladder with air. Gas release from the anal opening is often observed when the fish is scared or during ascent and descent. Here, the sounds produced by such a gas release are studied. The fish was kept in a low-pressure chamber. As the ambient pressure was reduced, the gas in the swim bladder expanded and was emitted through the anal opening. Herring sounds were also recorded in a fish trap and in the field. The characteristic sound made by herring during gas release is denoted as the pulsed chirp. This pulsed chirp is 32-133 ms long (N = 11) and consists of a series of 7-50 (N = 11) transient pulses with a continuous reduction of the frequency emphasis (centroid frequency of first pulse 4.1 kHz and of last pulse 3.0 kHz, N = 11). The source level of the chirp is 73 ± 8 dB re 1 µPa rms (root mean square) at 1 m (N = 19). The pulsed chirp is not known to be produced by any other marine animal and may be a good fingerprint for identifying schools of clupeid fish by natural predators, fishery scientists and fishermen. A model for the generation of the pulsed chirp is presented and tested on existing data.

The method proposed in this paper provides a computational technique for solving acoustic scattering problems associated with arbitrarily shaped two-or three-dimensional fluid-filled bodies. In particular, using free-space Green's functions along with the associated boundary conditions on the surface of the body, a pair of coupled integral equations are derived. The equations are then solved by approximating scatterer geometry by either linear segments or triangular patches, for the two-or three-dimensional cases, respectively, and employing the method of moments. The method presented in this work is simple, efficient and applicable to truly arbitrary geometries. Numerical results are presented for certain canonical shapes and compared with other available data.

The results from two bottom backscattering experiments are described in this paper. These experiments occurred within about 1 km of each other but were separated by approximately five years (1999 and 2004). The experimental methods used in the second experiment were changed based on lessons learned in the first experiment. These changes and the motivation for them are discussed. The

les baleines à bosse mâles émettent des vocalises organisées et, pour certaines, répétées formant ainsi le leitmotiv d'un chant. Principalement, dans le but de mieux appréhender le comportement de ces baleines et notamment les interactions entre individus (mâle/mâle, mâle/femelle), plusieurs études sont actuellement menées sur ces chants. Dans cette étude, nous nous intéressons aux unités sonores, vocalises séparées par 2 silences, qui composent ces chants, à leurs récurrences, et à leurs structurations. Cependant, tous ces paramètres dépendent de l'année et du lieu d'enregistrement. Des travaux antérieurs ont souligné la nécessité de méthodes objectives pour la classification de ces unités sonores. L'analyse détaillée des vocalisations a montré que les caractéristiques d'une unité peuvent changer brusquement pendant toute sa durée, ce qui les rend difficiles à caractériser et à grouper systématiquement. Cet article propose un codage parcimonieux des chants afin de déterminer leurs composantes stables de celles qui varient, pour différentes échelles de temps. Une définition de la complexité du code est également proposée afin de séparer les composantes Traitement du signal-n o 3-4-5/2013, 219-242

An increasing demand to explore the vast ocean floor for various purposes has made it necessary to deploy networks of underwater unmanned vehicles (UUVs) capable of carrying out multiple tasks. For information transfer among these vehicles, it is essential to design efficient communication systems and techniques which reduce the transmission error thereby improving system performance. The network consists of underwater components which perform activities such as communicating with each other using sound waves, gathering information and transmitting this information to the surface buoys which forward the data to a receiver onshore or on board some ship. This report studies the use of Carrier Interferometry (CI) spreading codes in underwater networks which use DS-CDMA technique for transmitting data. A network model has been presented and performance of DS-CDMA/CI has been studied for this model through simulations. The performance of this system has also been compared to those networks using Walsh-Hadamard (WH) codes to prove that DS-CDMA/CI is a better transmission scheme as compared to DS-CDMA/WH. Furthermore, multirate transmission in underwater environment has also been explored with the use of DS-CDMA/CI simulations. The results have shown that DS-CDMA/CI is an excellent candidate for future single rate as well as multirate transmission schemes.

Production of sound is a popular terminology in fish biology. Usually, fish and mammals produce sounds to attract
mates, continue communication among them and sometimes without any reasons. These sounds have a significant impact on
ecological research and management because passive acoustic fishery monitoring depends on it. In this study, we have mainly
worked on different mechanisms of sound production in fish and mammals. We have depicted the characteristics of fish sounds.
And finally, we have generated fish sounds from simulation using their practical characteristics. MATLAB was used as simulation
tool in this research.

The underwater acoustic channel is a complicated and time-varying multipath channel, and many equalization algorithms have been researched and developed to overcome the difficulties for underwater acoustic communication. Unfortunately, many algorithms are computational intensive and prone to lose convergence due to their sensitiveness to different channel configurations. In this paper, a pulse position modulation (PPM) scheme is proposed, and it uses two M-sequences of low cross-correlation to transfer information, which are modulated on two orthogonal carriers. One is used as a reference sequence, and the other is shifted relative to the reference. Information is carried by the starting time difference between the two sequences in each symbol. Comparing with conventional direct-sequence spread spectrum technique, the proposed scheme is more spectral efficient. Two receiver designs are given, one takes advantages of M-sequences' auto-correlation properties, and the other is motivated by passive phase conjugation (PPC) to take advantages of the channel. Combined with M-sequence, PPC performance is augmented without a receiving array to cover the water column, and it is far less complex than adaptive equalizers for receivers. Results from lake field trials are analyzed, and they verify potential applications of this PPM scheme.

Underwater Acoustic methods have been extensively used to locate and identify marine objects. These applications include locating underwater vehicles, finding shipwrecks, imaging sediments and imaging bubble fields. Ocean is fairly transparent to sound and opaque to all other sources of radiation. Acoustics technology is the most effective tool for monitoring this environment because of the sound's ability to propagate long distance in water. We used single beam echo sounder to discriminate underwater objects. Development of the algorithm and applied it to detect and quantify underwater object such as fish, sea grass, and seabed. We found the detected target has different backscatter value.

A passive sonar array designed for tracking diving sperm whales in three dimensions from a single small vessel is presented, and the advantages and limitations of operating this array from a 6 m boat are described. The system consists of four free floating buoys, each with a hydrophone, built-in recorder, and global positioning system receiver ͑GPS͒, and one vertical stereo hydrophone array deployed from the boat. Array recordings are post-processed onshore to obtain diving profiles of vocalizing sperm whales. Recordings are synchronized using a GPS timing pulse recorded onto each track. Sensitivity analysis based on hyperbolic localization methods is used to obtain probability distributions for the whale's three-dimensional location for vocalizations received by at least four hydrophones. These localizations are compared to those obtained via isodiachronic sequential bound estimation. Results from deployment of the system around a sperm whale in the Kaikoura Canyon in New Zealand are shown.

Ultra-low power MSP430 MCU Master-slave architecture Underwater acoustic recorder Long-term deployment a b s t r a c t Reducing overall power consumption is core issue in low power, high sampling rate, large storage data loggers necessary for long-term underwater acoustics research and other applications. A low-power microprocessor MSP430 offers a solution for the development of long-term deployment remote systems. In this paper, we present a multi-MSP430, master-slave architecture to resolve the power limitation issue. The proposed design is scalable in nature. For every additional slave unit installed in the array, the data sampling and streaming rate can be increased proportionally. We demonstrate the advantages of this concept using a multi-channel underwater acoustic recorder with a 100 kHz sampling rate. The performance of the system is demonstrated by a field acoustic experiment in which the reflection coefficient of the seafloor is measured. The proposed architecture will be applicable to many underwater long-term deployment systems. With its flexibility in configuration and synchronization of multi-channel sampling, it also provides a simple architecture for the construction of hydrophone arrays.

The Hydata (short for hydro-data) sonobuoy was developed by Mr Robert Beharie during 2008-10 at the International Centre for Island Technology (ICIT).

It provides remote sensing of calibrated high-quality sound data in marine environments. Able to be remotely controlled, the system can also transmit data the control station. The unit has the possibility of easily being adapted for a variety of other data acquisition purposes with the addition or replacement of complementary measuring instrumentation.  The hydrophone can be set to any depth up to 28 m maximum (using the standard 30 m cable).  Most electrical parts are standard units which can be easily replaced. The hull structure was manufactured from uPVC with lid machined for the fitment of double waterproof seals and dust seal.

The system consists of the sonobuoy unit and can be remotely controlled, if required, by a remote station from a vessel or the shore.  Range and speed of the data communication link depends on sea-state and directional antenna accuracy from the remote station.  Typical data transmission performance 54Mbps <1km to 1Mbps at 2km.

The Comprehensive Nuclear Test-Ban Treaty (CTBT) calls for the establishment of networks of seismic, hydroacoustic, infrasonic, and radionuclide sensors to monitor the earth for unannounced underground, underwater, and atmospheric nuclear tests. Seismic processing at the prototype International Data Center (pIDC) has been operating continuously since the GSETT-3 experiment that started in late 1994. Seismic is the most mature of the four monitoring technologies in automatic processing and interactive analysis. The other three technologies are in an earlier stage of development and evaluation. Since late 1996, efforts have been made under the Multi-Sensor Data Fusion project funded by the Defense Threat Reduction Agency (DTRA) to integrate hydroacoustic and infrasonic monitoring technologies into the existing pIDC automatic processing and interactive review framework. Signal processing of hydroacoustic and infrasonic waveform data was integrated into the pIDC monitoring system, and n...

Subsea Metrology exercise are very critical in subsea field development due to there use in subsea tie-in operations. Despite this criticality, there are limited papers detailing the advancement of different methods of carrying out this exercise in one single paper and where there is, there tends to be specific emphasis placed on the more popular methods like Acoustic LBL Metrology. This paper goes beyond this method and looks at newer and less common methods as well as the equipment that are building blocks of all metrology methods in use in the industry from the relatively shallow waters of the North Sea to the deeper waters of West Africa. This culminates in the look at a few case studies of comparison of different methods and use of combination of two or more methods to accurately generate measurements of the spool piece for connecting flange hubs in the Subsea Environment. 51017472! iii! Acknowledgement: I would like to specially thank my Technical Manager, Dave Bowden for his support in the course of writing this thesis and especially during the information gathering stage of the thesis. I would also like to thank Trevor Phillips from Technip for his advice, time and effort in going through the case studies with me and Sonardyne's Technical Manager, Ed Moller for support during the formative stage of the study especially regarding the equipment used and technology behind them.

Acoustics is the basics of the most important technologies for underwater telecommunication, as well as for target detection and identification in the aquatic media. Multiple frequency measurements are the key for species discrimination and open the door for sustainable fisheries. The development of wider broadband systems and quantitative multi-beam sonars and processing techniques constitute the present challenge for scientists and developers. In parallel, simpler and cost-efficient systems like satellite buoys can offer clue information for marine ecosystem monitoring or target species fisheries.

Avances y análisis del desarrollo de la Arqueología Subacuática en la Península de Yucatán durante su 10 Aniversario de su oficina en la región. Subdirección de Arqueología Subacuática, Sede INAH Campeche, México.

Ponencia presentada en la Tercera Convención Mexicana de Hidrografía. La batimetría impulsando el desarrollo económico sustentable.
Ciudad del Carmen, Campeche. Del 27 al 29 de abril, 2016.

Designing sounds in contemporary times has been very extensive and variety, as well as for movies, music, games, and so on. One of which is designing underwater sounds. There are many ways to create and design this sounds. To investigate the best way, it is necessary to research on ways to record underwater sounds and discuss the advantages and disadvantages of each method.
Data collection was done by using literature, case/project studies, as well as communication techniques, namely by distributing questionnaires to the respondents and conduct interviews to experts. The results collected from case/project studies are analyzed and measured by using spectrogram and spectrum analyzer for objective review. Then do analysis and validated by distributing questionnaires to 32 respondents with four different categories and conduct interviews to experts for subjective review.
From the results of this research, dynamic and condenser microphone can be used as another option other than hydrophone to record underwater sounds.

The word acoustics originates from the Greek word meaning "to listen." The original meaning concerned only hearing and sound perception. The word has gradually attained an extended meaning and, in addition to its original sense, is now commonly used for almost everything connected with rapidly varying mechanical vibrations, from noise to seismic and sonar systems, to ultrasound in medical diagnosis and materials technology. An important technical application of acoustics is related to undersea activities, where acoustic waves are used in much the same way that radar and electromagnetic waves are used on land and in the air-for the detection and location of objects, and for communications. The reason that acoustic rather than electromagnetic waves are used in seawater is simple: electromagnetic waves are strongly attenuated in salt water and would, therefore, have too short a range to be useful for most applications. This paper gives an introduction to underwater acoustics and an overview of the field of sonar engineering with emphasis on factors that affect range and performance.

This thesis introduces a new procedure for the enhancement of acoustic images of the bottom of the sea produced by side-scan sonars. Specifically, it addresses the problem of estimating and correcting geometric distortions frequently observed in such images as a. consequence of motion instabilities of the sonar array. This procedure estimates the geometric distortions from the image itself, without requiring any navigational or attitude measurements. A mathematical model for the distortions is derived from the geometry of the problem, and is applied to estimates of the local degree of geometric distortion obtained by cross-correlating segments of adjacent lines of the image. The model parameters are then recursively estimated through deterministic least-squares estimation. An alternative approach based on adaptive Kalman filtering is also proposed, providing a natural framework in which a priori information about the array dynamics may be easily incorporated. The estimates of the parameters of the distortion model are used to rectify the image, and may also be used for estimating the attitude parameters of the array. A simulation is employed to evaluate the effectiveness of this technique and examples of its application to high-resolution side-scan sonar images are provided.

In marine biodiversity conservation, population size estimation of marine species is the most significant challenge. Many top-notch researches have been conducted for estimating the population size of fish and mammals. Most of the researches followed mainly two methods namely non-acoustics and acoustics techniques to estimate fish population. The non-acoustic technique is an old terminology and a number of mechanical instruments are required to implement this technique. Consequently, acoustic methods for estimating fish population become popular. Acoustic techniques can be classified into two ways, i.e., active acoustic techniques, and passive acoustic techniques. In this paper, we have reviewed the major non-acoustic and acoustic techniques for estimating the population size of fish and mammals. At the same time, performance analysis among these techniques has been discussed in this study. An introduction to the diversity in fish population estimation techniques is the aim of this investigation.

Mediante  el  análisis  de  señales  acústicas  producto  de  embarcaciones  sobre  el  agua  tomadas  en campo,  se  desarrolló  un  algoritmo  para  la  detección,  clasificación  y  localización  de  dichas embarcaciones.  Además  se  tuvieron  en  cuenta  condiciones  de  operación  de  las  embarcaciones como lo son: la carga, la velocidad y condiciones propias del medio de propagación como lo es el ruido  ambiente.  Las  mediciones  se  realizaron  en  condiciones  controladas  con  embarcaciones  de prueba  en  una  piscina  olímpica,  en  donde  variables  como  las  dimensiones,  la  temperatura  y  la profundidad de esta, fueron determinadas. Además se contó con grabaciones realizadas en campo (Cartagena, Colombia), con las cuales se verificó el funcionamiento del algoritmo con señales de embarcaciones reales y diferentes señales de ruido ambiente.Para  los  registros  con  diferentes  condiciones  de  operación  de  las  embarcaciones  de  prueba,  se realizaron tomas a diferentes velocidades y con diferentes cargas (peso), para luego ser ingresados en  el  algoritmo.  Por  último,  el  desarrollo  de  este  se  basó  en  métodos  paramétricos  para  la estimación de densidad espectral de potencia (PSD) para señales aleatorias como lo son las señales de las diferentes embarcaciones analizadas en este trabajo.

La Fundación Malpelo, ha sido pionera en Colombia en el uso de nuevas técnicas para el estudio de las poblaciones de tiburones;
tal como la telemetría acústica. Con el objetivo de determinar si hay residencia de las especies Triaenodon obesus y Carcharhinus
galapagensis en el Santuario de Flora y Fauna Isla de Malpelo, se usaron tags acústicos V16 y receptores localizados alrededor de la isla, determinando patrones y diferencias para estas especies.

Sistem penentuan posisi akustik bawah laut adalah sistem penentuan posisi yang menggunakan prinsip hidro-akustik dalam menentukan posisi suatu objek yang ada di bawah laut. Karena gelombang elektromagnetik sangat lemah ketika di bawah air maka dalam menentukan posisi suatu objek di bawah laut menggunakan gelombang akustik. Ada berbagai macam metode yang dipakai dan tiap-tiap metode memiliki kelebihan dan kekurangannya masing-masing.

Just as fine particles such as those in muddy water obstruct our view optically, gas bubbles absorb and scatter sound to a great extent as well. This thesis outlines the theory and develops a model for the acoustic scattering of a common occurrence in the sea: a ship's wake. Using this model, underwater acousticians will be able to more accurately predict acoustic scattering from these formations. It's important to note that this model will be publicly available, whereas other models of this sort are not.

In recent years, the use of multibeam sonar to investigate and interpret the underwater landscape has increased substantially. Its advancement has allowed marine archaeologists to study areas underwater not previously accessible and its non-intrusive nature has positive implications for archaeological methodology and conservation – especially in terms of the spatial investigation and interpretation of archaeological features underwater. A close examination of the newest version of multibeam sonar, in contrast to the more commonly applied side scan sonar as demonstrated in projects in Norway and Scotland, allows us to see its superiority. Recent case studies of marine archaeology using multibeam sonar in Ireland, Slovenia and France, and the particularities of its application, also illustrate this and will further shed light on present challenges posed by its use. An analysis of multibeam sonar's strengths shows it to be the underwater remote sensing technology with the most interpretative potential and future. This includes the efficient capturing of high-resolution images, which affords archaeologists the opportunity to view features from many angles as well as from behind. While single-beam sonar has dominated the discipline, due to its accessibility and low-cost, multibeam sonar, because of its superior imaging ability, is clearly the best choice to non-intrusively investigate archaeological sites underwater in greater detail.

The paper addresses the general problem of estimating the position of an underwater target carrying an acoustic emitter by measuring the times of arrival (TOAs) of the acoustic signals at a set of surface buoys equipped with submerged hydrophones and GPS receivers. Examples of underwater targets of interest include AUVs (Autonomous Underwater Vehicles) and ROVs (Remotely Operated Vehicles) as well as manned submersibles, divers, and even marine animals. When compared with classical systems, the class of underwater acoustic positioning systems considered in this paper is far more versatile and portable and the costs of operation are greatly reduced. This justifies the increasing interest that such systems have received over the past few years, both from a theoretical and practical standpoint. Research and development in this area have progressed to the point where a commercial product made its appearance in the market: the so-called GIB (GPS Intelligent Buoys). However, much work remains to be done towards the development of operational systems capable of yielding adequate performance in the presence of multi-path effects and acoustic outliers. The paper gives a brief overview of this area of research and discusses theoretical and practical issues that arise in the development and operation of acoustic positioning systems at sea.

The fundamental principles of acoustic theory and its application to structural vibrations and the interactions of elastic structures with acoustic media are presented in an introductory textbook for graduate students of engineering and applied physics. Chapters ...

The pollution monitoring system describes the processes and
activities that need to implement through monitor the quality of specific
environment. In this thesis those activities and processes are presented by
assuming two important areas, the design of underwater wireless sensor
network and a proposal water quality index in Iraq using fuzzy inference
system.
In the first area (design of underwater wireless sensor network),thesis
focus on the performance assessment of five underwater wireless sensor
network (UWSN) Media Access Control (MAC) layer protocols namely;
(Broadcast MAC, Aloha, R-MAC, FAMA, and UWAN_MAC). These
protocols are used for the water environment in terms of energy
consumption and received throughput. Three of them are nominated
based on some previous assessment. They were compared in terms of
total drop packets and average end to end delay. Subsequently, an
investigation of the facts about what is the robust and energy efficient
routing protocol in underwater wireless sensor networks is presented.
This is done by comparing three important routing protocols, namely;
Vector-Based Forwarding Protocol (VBF), hop-by-hop vector-based
forwarding (HHVBF) and Vector-Based Void Avoidance (VBVA). The
performance evaluation of these protocols is achieved using metrics
energy consumption, average end-to-end delay and Packet delivery ratio.
Results of these evaluations and comparisons prove that UW-MAC
protocol is the most suited one with geographic routing protocols
especially VBF. Assessment is carried out by using Aqua-Sim simulators
for underwater sensor networks and NS2 based simulator installed in
Linux environment.
A robust and flexible index was made to be used as baseline for
all pollutants that need to be monitored. This has been done with fuzzy
inference system to present a work aimed to propose water quality index
in Iraq. Fuzzy logic is used for developing the traditional environmental
indices to eliminate the routine in assessment of water quality. As well as
to overcome the largest problems uncertainty and subjectivity in
traditional way; we called "FWQI". To evaluate the performance of the
index suggested with the real conditions, the case study was conducted on
Tigris River, Iraq. The data of water quality from different sampling
positions were taken. It was found that the achieved results from Fuzzy
Water Quality Index (FWQI) are less than the results obtained from the
regular method in final score of pollution by approximately 41.64% for a
specified period.

A shipwreck was discovered in deep-water during a systematic side-scan sonar survey conducted in 2007 by Malta's heritage authorities and the University of Malta. Located off the coast of the island of Gozo, Malta, this site was the subject of a series of further in-depth studies that spanned over 10 years. Throughout this period, a number of different technologies were used to explore, record and study the site. This paper provides an overall description, analysis and evaluation of the various technologies and methodologies used to investigate this site.

Multipath arrivals in many underwater acoustic channels are often cross-correlated and as
a result, the path cross-correlation matrix shows a smaller rank than the number of multipath
delay taps. Channel tracking error, measured in terms of the signal prediction error,
can be significantly reduced by tracking the channel components in the signal subspace as
previously demonstrated for a slowly varying channel in which the signal basis vectors can
be assumed to be time-invariant. For a rapidly time-varying channel, one needs to track the
time variation of the signal basis vectors. A subspace tracker is used in this paper to track
the time variation of the signal basis vectors based on a coarse estimate of the channel
impulse response (CIR). The signal amplitudes (channel components) are tracked using:
(1) a recursive-least-square method and (2) a Kalman filter based on a state-space model.
Performance of the proposed algorithms is demonstrated with real sea data. One finds that
even for a rapidly time-varying channel, the channel impulse response can be tracked accurately.
For the data analyzed, the signal prediction errors are reduced by 12 dB using the
algorithms proposed in this paper compared with that using the conventional approaches

To date most sonars use narrow band pulses and often only the echo envelope is used for object detection and classification. This paper considers the advantages afforded by bio-inspired sonar for object identification and classification through the analysis and the understanding of the broadband echo structure. Using the biomimetic dolphin based sonar system in conjunction with bio-inspired pulses developed from observations of bottlenose dolphins performing object identification tasks, results are presented from experiments carried out in a wave tank and harbor. In these experiments responses of various targets to two different bio-inspired signals are measured and analyzed. The differences in response demonstrate the strong dependency between signal design and echo interpretation. In the simulations and empirical data, the resonance phenomena of these targets cause strong notches and peaks in the echo spectra. With precision in the localization of these peaks and dips of around 1 kHz, the locations are very stable for broadside insonification of the targets and they can be used as features for classification. This leads to the proposal of a broadband classifier which operates by extracting the notch positions in the target echo spectra.