A Geometry-Based Underwater Acoustic Channel Model Allowing for Sloped Ocean Bottom Conditions

Nivå

Modelling, Analysis, and Simulation of Underwater Acoustic Channels : Doctoral Dissertation for the Degree Philosophiae Doctor (PhD) at the Faculty of Engineering and Science, Specialization in Information and Communication Technology

publishedVersio

Parameter dependence of acoustic mode quantities in an idealized model for shallow-water nonlinear internal wave ducts

Author Posting. © Acoustical Society of America, 2019. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 146(3), (2019): 1934-1945, doi:10.1121/1.5125261.Nonlinear internal waves in shallow water have significant acoustic impacts and cause three-dimensional ducting effects, for example, energy trapping in a duct between curved wavefronts that propagates over long distances. A normal mode approach applied to a three-dimensional idealized parametric model [Lin, McMahon, Lynch, and Siegmann, J. Acoust. Soc. Am. 133(1), 37–49 (2013)] determines the dependence of such effects on parameters of the features. Specifically, an extension of mode number conservation leads to convenient analytical formulas for along-duct (angular) acoustic wavenumbers. The radial modes are classified into five types depending on geometric characteristics, resulting in five distinct formulas to obtain wavenumber approximations. Examples of their dependence on wavefront curvature and duct width, along with benchmark comparisons, demonstrate approximation accuracy over a broad range of physical values, even including situations where transitions in mode types occur with parameter changes. Horizontal-mode transmission loss contours found from approximate and numerically exact wavenumbers agree well in structure and location of intensity features. Cross-sectional plots show only small differences between pattern phases and amplitudes of the two calculations. The efficiency and accuracy of acoustic wavenumber and field approximations, in combination with the mode-type classifications, suggest their application to determining parameter sensitivity and also to other feature models.This work was supported by the Office of Naval Research under grants to Rensselaer Polytechnic Institute (Grant Nos. N00014-14-1-0372 and N00014-17-1-2370) and to Woods Hole Oceanographic Institution (Grant Nos. N00014-11-1-0701 and N00014-17-1-2692). Additional funding was provided by Naval Undersea Warfare Center Division Newport through the SMART Scholarship for the first author's doctoral degree program. The authors also thank Dr. Timothy F. Duda of WHOI and Dr. David Wells of University of North Carolina at Chapel Hill for their assistance with this paper.2020-03-3

ACOUSTIC METHODS FOR MAPPING AND CHARACTERIZING SUBMERGED AQUATIC VEGETATION USING A MULTIBEAM ECHOSOUNDER

Submerged aquatic vegetation (SAV) is an important component of many temperate global coastal ecosystems. SAV monitoring programs using optical remote sensing are limited by water clarity and attenuation with depth. Here underwater acoustics is used to analyze the water volume above the bottom to detect, map and characterize SAV. In particular, this dissertation developed and applied new methods for analyzing the full time series of acoustic intensity data (e.g., water column data) collected by a multibeam echosounder. This dissertation is composed of three separate but related studies. In the first study, novel methods for detecting and measuring the canopy height of eelgrass beds are developed and used to map eelgrass in a range of different environments throughout the Great Bay Estuary, New Hampshire, and Cape Cod Bay, Massachusetts. The results of this study validated these methods by showing agreement between boundaries of eelgrass beds in acoustic and aerial datasets more in shallow water than at the deeper edges, where the acoustics were able to detect eelgrass more easily and at lower densities. In the second study, the methods developed for measuring canopy height in the first study are used to delineate between kelp-dominated and non-kelp-dominated habitat at several shallow rocky subtidal sites on the Maine and New Hampshire coast. The kelp detection abilities of these methods are first tested and confirmed at a pilot site with detailed diver quadrat macroalgae data, and then these methods are used to successfully extrapolate kelp- and non-kelp-dominated percent coverages derived from video photomosaic data. The third study examines the variability of the acoustic signature and acoustically-derived canopy height under different tidal currents. Submerged aquatic canopies are known to bend to accommodate the drag they generate in response to hydrodynamic forcing, and, in turn, the canopy height measured by acoustics will not be a perfect representation of canopy height as defined by common seagrass monitoring protocols, which is usually measured as the length of the blade of seagrass. Additionally, the bending of the canopy affects how the blades of seagrass are distributed within the footprint of the sonar, changing the acoustic signature of the seagrass canopy. For this study, a multibeam echosounder, a current profiler and an HD video camera were deployed on a stationary frame in a single eelgrass bed over 2 tidal cycles. Acoustic canopy heights varied by as much as 30 cm over the experiment, and although acoustic canopy height was correlated to current magnitude, the relationship did not follow the predictive flexible vegetation reconfiguration model of Luhar and Nepf (2011). Results indicate that there are significant differences in the shape of the return from a deflected (i.e., bent-over) canopy and an upright canopy, and that these differences in shape have implications for the accuracy of bottom detection using the maximum amplitude of a beam time series. These three studies clearly show the potential for using multibeam water column backscatter data for mapping coastal submerged aquatic vegetation while also testing the natural variability in acoustic canopy height measurements in the field

3d Seafloor Model Determination And Change Detection With Multitemporal Multi Beam Echo Sounder Bathymetry

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2017Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2017Topografya yeryüzü üzerinde ve altında bulunan çeşitli yer şekillerini detayları ile inceleyen çalışmaların tanımlanmasıdır. Yeryüzündeki hareketlerin anlaşılması için detaylı topografik bilgiye ihtiyaç vardır. Okyanuslarda deniz tabanının yapısı, taban yüzeyinin özellikleri ile doğal oluşumlar ve insan yapılarını içeren coğrafi nitelikler topoğrafyanın kapsamına girmektedir. Bu kapsamda detaylı deniz haritalarının hazırlanması, fiziksel oşinografi, biyoloji, deniz jeolojisi ve jeofiziği gibi bilimler açısından önem arz etmektedir. Bunun yanında seyir haritalarının oluşturulması, deniz ulaşımı açısından da kritik öneme sahiptir. Bu ise hidrografik ölçümlerin ve ölçüm sistemlerinin gerekliliğini vurgulamaktadır. Deniz tabanının haritalanması için birçok teknik geliştirilmiştir. En ilkel tekniklerden birisi olan bir ipin ucuna bağlanmış ağırlığın suya daldırılması yoluyla yapılan el iskandili yönteminden, uydu tabanlı altimetrik sistemlere kadar birçok yöntem kullanılmıştır. Elektronik ve bilgisayar teknolojilerinin gelişmesi ile birlikte, modern ölçüm sistemleri daha hassas ve etkin hale gelmiştir. Günümüzde deniz ölçümleri için etkin kullanılan optik ve sonar sistemler bulunmaktadır. Optik sistemler içerisinde teknolojisi hızla gelişen Lidar sistemleri yeşil lazer ışını kullanarak su içerisine gönderdiği sinyallerin saçılımlarını derinlik verisi olarak değerlendirir. Görünebilirliğin yüksek olduğu sığ sularda etkin çalışan bu sistem, derinlik arttıkça ve görünürlük azaldıkça hassasiyetini ve etkinliğini kaybeder. İskandil sistemi ‘su yüksekliği’ olarak adlandırılan derinlik verisini üretebilmek için ses dalgasını kullanan modern tekniklerden birdir. Ses dalgası ile ölçüm yapan sistemler basitçe sesin suda gidiş ve dönüş hızını hesaplayarak derinlik verisi elde ederler. İskandiller bir seferde ölçebildikleri derinlik verisi sayısına göre sınıflandırılmıştır. Tek bimli iskandil (TBİ) sistemi bir seferde aletin nadiri doğrultusunda tek bir derinlik verisi üretir. Bunun yanında, çok bimli iskandil (ÇBİ), bir seferde yüzlerce derinlik ölçümü sağlayarak deniz tabanında %100 kaplama sağlamaktadır. Deniz haritası üretimi için çok bimli iskandil sistemleri kullanan hidrografi kurumları/şirketler hidrografik ölçüm standartlarına uygun olarak ölçüm yapmalıdırlar. Bu standartlar genellikle Uluslararası Hidrografi Örgütü (IHO) standartları ile uyumludur. Bazı örgütler doğrudan bu standartları kullanırken, bazıları ise bu standartlardan daha sıkı olan standartlar geliştirilmiştir. Çok bimli iskandil sistemleri; iskandil, konumlandırma sistemi ve hareket sensörü gibi senkronize bir şekilde çalışması gereken birçok ölçüm aletini içermektedir. Bundan dolayı sistem elemanlarının iyi bir kurulum ile tekneye monteleri gerçekleştirilmeli ve ölçüm teknesinin 3B uzayı içerisinde birbiriyle olan ilişkileri tanımlanmalıdır. Ölçümler öncesinde ‘patch testi’ olarak adlandırılan kalibrasyon prosedürü, kurulum ve aletlerin senkronizasyonundan kaynaklanan hataların giderilmesi için gerekmektedir. Bu test kapsamında, sinyal gecikmesi testi (latency), Y ekseni dönüklüğü (roll), X ekseni dönüklüğü (pitch) ve Z ekseni dönüklüğü (yaw) hataları hesaplanmıştır. Bunlarla birlikte, özellikle zamansal veri analizi ve 3B yüzey modellemesi için su kolonu boyunca gerçekleştirilen ses hızı ölçümleri ve su seviyesi değişimleri göz önünde bulundurulmuştur. Bu tezde göz önüne alınan çalışma bölgesi KKTC (Kuzey Kıbrıs Türk Cumhuriyeti) ‘Su Temini Projesi’ içerisinde yer alan, Anamur – KKTC ishale boru hattı güzergâhını kapsayan alandır. Bu proje, Türkiye’den Kuzey Kıbrıs Türk Cumhuriyeti’ne, Akdeniz’de deniz altından boru hatları ile içme ve sulama suyu temini amacı ile gerçekleştirilmiş olup, özellikleri bakımından dünyada benzeri bulunmayan uluslararası bir su iletim hattı projesidir. Proje 4 bölümden oluşmaktadır. Bu bölümlerden birincisi Anamur Alaköprü Barajı’ndan, Ören kasabasına kadar olan iletim hattı, ikincisi boru hatlarının kazı gemisi tarafından oluşturulmuş kanal içerisinde deniz ile buluştuğu bölüm, üçüncüsü projeyi bu boyutlarda yapılmış tek proje özelliğini kazandıran Akdeniz geçiş kısmı ve dördüncüsü ise KKTC kıyılarından Geçitköy barajına su taşınması kısmıdır. Akdeniz geçiş kısmını önemli yapan özelliği ise 500m uzunluğundaki yekpare boruların su seviyesinin 250m kadar altında askıda kalıp, çelik halatlar ile deniz tabanına monte edilmiş olmasıdır.Topography is the term that indicates the study of various landforms that exist on or below the Earth and a detailed knowledge of topography is required to understand the most Earth processes. In the oceans, sea floor topography refers the geographic features of the sea floor including the configuration of a surface and the position of its natural and man-made features; and detailed nautical charts are fundamental for many sciences such as physical oceanography, biology and marine geology. Besides, it is significant for navigational requirement. This revealed the necessity of hydrographic measurements and measurement systems. For this purpose, many techniques developed and used to create the map of the seafloor. From the first primitive technique which involved lowering a weighted line into the water to satellite derived altimetry many systems used for determination of seafloor. After the development of electronic and computer technology, the modern systems become more accurate and effective. An echo sounder system is one of the modern techniques that use the sound waves to determine the depth which is also called ‘sounding’. Echo sounders are classified with the capability of producing sounding in one time. Single beam echo sounder (SBES) system can produce single sounding in each measurement. Besides, multi beam echo sounder (MBES) system can produce hundreds of sounding in each measurement sets and provide 100% seafloor coverage. The hydrographic offices, which use the Multi Beam Echo Sounder (MBES) system for the establishment of nautical charts, have their own set of accuracy standards for hydrographic surveys, which generally comply with the standards defined by the International Hydrographic Organization (IHO). MBES systems include multiple measurement systems such as sonar head, positioning system, motion sensor that work in a synchronized manner. Therefore, the system components are installed and established to each other in 3D space of vessel. Before the measurements, the ‘Patch Test’ is required to eliminate the systematic errors due to instrumental synchronization and installation. In this test, signal delay test (latency), Y-axis rotation (roll), X-axis rotation (pitch), Z-axis rotation (yaw) errors are calculated. Besides, the effects of the sound velocity measurement through water column and the sea level changes need to be taken into consideration especially in the multi-temporal data analysis and 3D modeling. In this thesis, the seafloor of the Anamur -TRNC Drinking Water Pipeline route in the ‘Northern Cyprus Water Project’ is selected as a study area. This project, a unique in the world, is an international water diversion project designed to supply water for drinking and irrigation from southern Turkey to Northern Cyprus via pipeline under Mediterranean Sea. The dredged channels for pipe laying in the Anamur and TRNC shores are considered in this study and two MBES surveys are conducted in different periods to determine the surface differences. Multi temporal multi beam echo sounder measurements are used in the change analysis and surface modeling and the efficiency of this system is outlined together with its limitations.Yüksek LisansM.Sc

Measurements of shoaling internal waves and turbulence in an estuary

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 118 (2013): 273–286, doi:10.1029/2012JC008154.The shoaling of horizontally propagating internal waves may represent an important source of mixing and transport in estuaries and coastal seas. Including such effects in numerical models demands improvements in the understanding of several aspects of the energetics, especially those relating to turbulence generation, and observations are needed to build this understanding. To address some of these issues in the estuarine context, we undertook an intensive field program for 10 days in the summer of 2008 in the St. Lawrence Estuary. The sampling involved shore-based photogrammetry, ship-based surveys, and an array of moorings in the shoaling region that held both conventional and turbulence-resolving sensors. The measurements shed light on many aspects of the wave shoaling process. Wave arrivals were generally phase-locked with the M2 tide, providing hints about far-field forcing. In the deeper part of the study domain, the waves propagated according to the predictions of linear theory. In intermediate-depth waters, the waves traversed the field site perpendicularly to isobaths, a pattern that continued as the waves transformed nonlinearly. Acoustic Doppler velocimeters permitted inference of the turbulent energetics, and two main features were studied. First, during a period of shoaling internal waves, turbulence dissipation rates exceeded values associated with tidal shear by an order of magnitude. Second, the evolving spectral signatures associated with a particular wave-shoaling event suggest that the turbulence is at least partly locally generated. Overall, the results of this study suggest that parameterizations of wave-induced mixing could employ relatively simple dynamics in deep water, but may have to handle a wide suite of turbulence generation and transport mechanisms in inshore regions.The work was supported by the Killam Foundation, the Natural Sciences and Engineering Research Council of Canada, the Canadian Foundation for Innovation, the Canadian Foundation for Climate and Atmospheric Sciences, and the Canadian Department of Fisheries and Oceans.2013-07-3

Underwater Localization in a Confined Space Using Acoustic Positioning and Machine Learning

Localization is a critical step in any navigation system. Through localization, the vehicle can estimate its position in the surrounding environment and plan how to reach its goal without any collision. This thesis focuses on underwater source localization, using sound signals for position estimation. We propose a novel underwater localization method based on machine learning techniques in which source position is directly estimated from collected acoustic data. The position of the sound source is estimated by training Random Forest (RF), Support Vector Machine (SVM), Feedforward Neural Network (FNN), and Convolutional Neural Network (CNN). To train these data-driven methods, data are collected inside a confined test tank with dimensions of 6m x 4.5m x 1.7m. The transmission unit, which includes Xilinx LX45 FPGA and transducer, generates acoustic signal. The receiver unit collects and prepares propagated sound signals and transmit them to a computer. It consists of 4 hydrophones, Red Pitay analog front-end board, and NI 9234 data acquisition board. We used MATLAB 2018 to extract pitch, Mel-Frequency Cepstrum Coefficients (MFCC), and spectrogram from the sound signals. These features are used by MATLAB Toolboxes to train RF, SVM, FNN, and CNN. Experimental results show that CNN archives 4% of Mean Absolute Percentage Error (MAPE) in the test tank. The finding of this research can pave the way for Autonomous Underwater Vehicle (AUV) and Remotely Operated Vehicle (ROV) navigation in underwater open spaces

Intelligent deployment strategies for passive underwater sensor networks

Passive underwater sensor networks are often used to monitor a general area of the ocean, a port or military installation, or to detect underwater vehicles near a high value unit at sea, such as a fuel ship or aircraft carrier. Deploying an underwater sensor network across a large area of interest (AOI), for military surveillance purposes, is a significant challenge due to the inherent difficulties posed by the underwater channel in terms of sensing and communications between sensors. Moreover, monetary constraints, arising from the high cost of these sensors and their deployment, limit the number of available sensors. As a result, sensor deployment must be done as efficiently as possible. The objective of this work is to develop a deployment strategy for passive underwater sensors in an area clearance scenario, where there is no apparent target for an adversary to gravitate towards, such as a ship or a port, while considering all factors pertinent to underwater sensor deployment. These factors include sensing range, communications range, monetary costs, link redundancy, range dependence, and probabilistic visitation. A complete treatment of the underwater sensor deployment problem is presented in this work from determining the purpose of the sensor field to physically deploying the sensors. Assuming a field designer is given a suboptimal number of sensors, they must be methodically allocated across an AOI. The Game Theory Field Design (GTFD) model, proposed in this work, is able to accomplish this task by evaluating the acoustic characteristics across the AOI and allocating sensors accordingly. Since GTFD considers only circular sensing coverage regions, an extension is proposed to consider irregularly shaped regions. Sensor deployment locations are planned using a proposed evolutionary approach, called the Underwater Sensor Deployment Evolutionary Algorithm, which utilizes two suitable network topologies, mesh and cluster. The effects of these topologies, and a sensor\u27s communications range, on the sensing capabilities of a sensor field, are also investigated. Lastly, the impact of deployment imprecision on the connectivity of an underwater sensor field, using a mesh topology, is analyzed, for cases where sensor locations after deployment do not exactly coincide with planned sensor locations

Laboratory measurements of the sound generated by breaking waves

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution December 1991Breaking waves dissipate energy, transfer momentum from the wind to surface currents and breaking enhances the transfer of gas and mass across the air-sea interface. Breaking waves are believed to be the dominant source of sea surface sound at frequencies greater than 500 Hz and the presence of breaking waves on the ocean surface has been shown to enhance the scattering of microwave radiation. Previous studies have shown that breaking waves can be detected by measuring the microwave backscatter and acoustic radiation from breaking waves. However, these techniques have not yet proven effective for studying the dynamics of breaking. The primary motivation for the research presented in this thesis was to determine whether measurements of the sound generated by breaking waves could be used to quantitatively study the dynamics of the breaking process. Laboratory measurements of the microwave backscatter and acoustic radiation from two-dimensional breaking waves are described in Chapter 2. The major findings of this Chapter are: 1) the mean square acoustic pressure and backscattered microwave power correlate with the wave slope and dissipation for waves of moderate slope, 2) the mean square acoustic pressure and backscattered microwave power correlate strongly with each other, and 3) the amount of acoustic energy radiated by an individual breaking event scaled with the amount of mechanical energy dissipated by breaking. The observed correlations with the mean square acoustic pressure are only relevant for frequencies greater than 2200 Hz because lower frequencies were below the first acoustic cut-off frequency of the wave channel. In order to study the lower frequency sound generated by breaking waves another series of two-dimensional breaking experiments was conducted. Sound at frequencies as low as 20 Hz was observed and the mean square acoustic pressure in the frequency band from 20 Hz-l kHz correlated strongly with the wave slope and dissipation. A characteristic low frequency signal was observed immediately following the impact of the plunging wave crest. The origin of this low frequency signal was found to be the pulsating cylinders of air which are entrained by the plunging waves. The pulsation frequency correlated with both the wave slope and dissipation. Following the characteristic constant frequency signal, approximately 0.25 s after the initial impact of the plunging crest, another low frequency signal was typically observed. These signals were generally lower in frequency initially and then increased in frequency as time progressed. To determine if three-dimensional effects were important in the sound generation process and to measure the sound beneath larger breaking waves a series of experiments was conducted in a large multi-paddle wave basin. Three-dimensional breaking waves were generated and the sound produced by breaking was measured in the frequency range from 10 Hz to 20 kHz. The observed sound spectra showed significant increases in level across the entire bandwidth from 10 Hz to 20 kHz and the spectra sloped at -5 to-6 dB per octave at frequencies greater than 1 kHz. The mean square acoustic pressure in the frequency band from 10 Hz to 150 Hz correlated with the wave amplitude similar to the results obtained in the two-dimensional breaking experiments. Large amplitude low frequency spectral peaks were observed approximately 0.75 s after the initial impact of the plunging crests. It was postulated that the low frequency signals observed some time after the initial impact of the plunging crests for both the two and three-dimensional breakers were caused by the collective oscillation of bubble clouds. Void fraction measurements taken by Eric Lamarre were available for five breaking events and therefore the average sound speed inside the bubble clouds and their radii were known. Using this information the resonant frequencies of a two-dimensional cylindrical bubble cloud of equal radius and sound speed were calculated. The frequencies of the observed signals matched closely with the calculated resonant frequencies of the first and second mode of the two-dimensional cylindrical bubble cloud. The close agreement supports the hypothesis that the low frequency signals were produced by the collective oscillation of bubble clouds. In Chapter 4 a model of the sound produced by breaking waves is presented which uses the sound radiated by a single bubble oscillating at its linear resonant frequency and the bubble size distribution to estimate the sound spectrum. The model generates a damped sinusiodal pulse for every bubble formed, as calculated from the bubble size distribution. If the range to the receiver is known then the only unknown parameters are ε, the initial fractional amplitude of the bubble oscillation and L, the dipole moment arm or twice the depth of the bubble below the free surface. It was found that if the product εxL is independent of the bubble radius the model reproduces the shape and magnitude of the observed sound spectrum accurately. The success of the model implies that it may be possible to calculate the bubble size distribution from the sound spectrum. The model was validated using data from experiments where the breaking events were small scale gently spilling waves (Medwin and Daniel, 1990)