OCEANS 2006 - Asia Pacific最新文献

{"title":"Numerical Analysis of an Underwater Acoustic Lens System for Ambient Noise Imaging using Finite Difference Time Domain Method","authors":"K. Mori, A. Miyazaki, H. Ogasawara, T. Yokoyama, T. Nakamura","doi":"10.1109/OCEANSAP.2006.4393831","DOIUrl":"https://doi.org/10.1109/OCEANSAP.2006.4393831","url":null,"abstract":"Ambient noise imaging (ANI) is the revolutionary idea of detecting undersea objects using the ocean's background noise. In this study, in order to realize an ANI system, sound fields focused by an acoustic lens system constructed with a single biconcave lens were analyzed using the 2D finite difference time domain (FDTD) method. By comparing the image points and -3 dB areas obtained by lenses with various apertures A and radii R of curvature, sufficient resolution, e.g., a beam width of 1 deg at 60 kHz, was observed using a lens of A = R = 2.0 m. In another 2D FDTD analysis, rigid target objects in an acoustic noise field generated by a large number of point sources were successfully detected using the lens determined above. The noise sources were supposed to be not only at front-light but also backlight positions. The difference in spectra levels between the target direction and the others was greater than 5 dB over 40 kHz for front-light or 50 kHz in back-light sources.","PeriodicalId":268341,"journal":{"name":"OCEANS 2006 - Asia Pacific","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126907550","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Distributed Space-Time Cooperative Schemes for Underwater Acoustic Communications","authors":"M. Vajapeyam, U. Mitra, J. Preisig, M. Stojanovic","doi":"10.1109/OCEANSAP.2006.4393898","DOIUrl":"https://doi.org/10.1109/OCEANSAP.2006.4393898","url":null,"abstract":"In resource limited, large scale underwater sensor networks, cooperative communication over multiple hops offers opportunities to save power. Intermediate nodes between source and destination act as cooperative relays. Herein, protocols coupled with space-time block code (STBC) strategies are proposed and analyzed for distributed cooperative communication. Amplify-and-forward type protocols are considered, in which intermediate relays do not attempt to decode the information. The Alamouti-based cooperative scheme for flat-fading channels is modified in order work in the presence of multipath, which is a main characteristic of underwater acoustic channels. A time-reversal distributed space-time block code (TR-DSTBC) is employed, which extends the classical TR-STBC approach to a cooperative communication scenario. We show that, just like in the multi-antenna STBC case, TR along with the orthogonality of the DSTBC essentially allows for decoupling of the vector ISI detection problem into separate scalar problems, and therefore significant complexity reduction.","PeriodicalId":268341,"journal":{"name":"OCEANS 2006 - Asia Pacific","volume":"74 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126460030","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Results From A High-Resolution Acoustic Device For Monitoring Finless Porpoises In Coastal Precincts Off Japan","authors":"T. Ura, R. Bahl, M. Yano, T. Inoue, T. Sakamaki, T. Fukuchi","doi":"10.1109/OCEANSAP.2006.4393865","DOIUrl":"https://doi.org/10.1109/OCEANSAP.2006.4393865","url":null,"abstract":"Finless porpoise populations in coastal precincts are adversely impacted by human activities that cause water pollution, lack of food and denial of migratory paths. Proper survey and management of their populations has therefore become necessary. Visual-based surveys are very tedious, labor intensive, have limited accuracy, and are strongly subject to visibility conditions. These cetaceans produce characteristic echolocation pulses that make them acoustically visible, night or day. Acoustic-based survey methods are expected to be indispensable for surveying finless porpoises that do not exhibit visually dramatic behavior like the oceanic dolphins and spend most of their time underwater. Passive observation of echolocation clicks on arrays of high frequency hydrophones can simultaneously localize several underwater sound sources as they move around. Since the click characteristics are known to be species-specific, individuals belonging to the same group need to be precisely discriminated on basis of their location and movement pattern alone. This paper reports the results from testing a compact and portable acoustic survey device designed for monitoring underwater behavior of groups finless porpoises. The acoustic sensor system consists of 3 hydrophones forming a main vertical linear array, together with two more hydrophones forming a small 3-element triangle array with the central hydrophone, in a plane perpendicular to the linear array axis. It is housed in a \"bird-cage\" structure that weighs 25 kg and is 3.6 m tall, 30 cm in diameter, and is deployed vertically with a buoy and a weight. The device has been tested in shallow waters of less than 10 meters depth off-Choshi port on the Pacific coast of Japan. Echolocation pulses from several porpoises were recorded. One feature has been the differences in strength of the click signal observed on the hydrophones in the vertical array that is indicative of a narrow beam pattern of the porpoise. The main challenge in localization has been to eliminate surface and bottom reflections that inevitably occur in shallow water. In addition, echolocation pulses of some dolphins in the vicinity were also simultaneously recorded. An attempt has been made to segregate the porpoise clicks from those of the dolphins, and then to localize the porpoises. The experiment demonstrates the capability of the device for individually tracking several vocalizing animals. This novel tracking system will be used to survey populations of finless porpoises in coastal precincts.","PeriodicalId":268341,"journal":{"name":"OCEANS 2006 - Asia Pacific","volume":"101 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123750538","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Numerical Model for Wave Diffraction in Fully Nonlinear Wave Tank","authors":"X.T. Zhang, B. Khoo, J. Lou","doi":"10.1109/OCEANSAP.2006.4393824","DOIUrl":"https://doi.org/10.1109/OCEANSAP.2006.4393824","url":null,"abstract":"A numerical model in the time domain is developed for a numerical wave tank (NWT) with the fully nonlinear (or exact) free surface boundary conditions. In this model, an indirect desingularized boundary element method (DBEM) is employed to solve the boundary value problem of velocity potential at each time step and the mixed Eulerian-Lagrangian (MEL) formulation is adopted to track the instantaneous free surface boundary. The ISOPE benchmark test example of wave diffraction by a fixed Lewis form body is studied using this model, and the numerical results are compared with the available data.","PeriodicalId":268341,"journal":{"name":"OCEANS 2006 - Asia Pacific","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122597537","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Denoising Dolphin Click Series in the Presence of Tonals, using Singular Spectrum Analysis and Higher Order Statistics","authors":"P. Seekings, J. Tan, J. Potter, M. Hoffman-Kuhnt, A. Pack, L. Herman","doi":"10.1109/OCEANSAP.2006.4393911","DOIUrl":"https://doi.org/10.1109/OCEANSAP.2006.4393911","url":null,"abstract":"We examine the use of Singular Spectrum Analysis (SSA) technique as an alternative technique to using standard wavelet shrinkage schemes for the purpose of de-noising mixtures of tonals, transients and Gaussian noise. Wavelet schemes require a calculation of a threshold to determine which components are taken to be signal and noise. If the noise component is Gaussian, then threshold can be determined by using an appropriate estimator. However, in the presence of strong tonal content the Gaussian threshold estimators do not give optimal performance. One method is to iteratively shift the threshold until some performance criterion has been maximized. However this frequently leads to over de-noising this time series. Since the wavelet basis is chosen to best represent the signal of interest, over de-noising can cause artifacts to appear similar to the signal of interest. In most applications this can not be tolerated. SSA has advantages in that the basis of decomposition is derived from the time series itself. So-called Empirical Orthogonal Functions (EOFs) are derived from a lag matrix created from the time series. Singular Value Decomposition (SVD) is then used to decompose a time series into a number of time series components. In the case of signal separation or de-noising the time series components can be combined by using their statistical properties. We examine the use of higher order statistics, to group components into tonals, transient, and Gaussian noise. By using the properties of the kurtosis for these three types of signal, the grouping of components can be done in a more formal manner, than the thresholding technique found in wavelet schemes. The technique is demonstrated on test data consisting of dolphin clicks in the presence of tonal and Gaussian noise. Results are also shown for real data of a dolphin click series while echo-locating on a target. It is critical for future work that after de-noising, the shape of the dolphin clicks is preserved, and the recorded reflections from the target are adequately de-noised, without introducing artifacts which could be mistaken for reflections. We discuss the results of the SSA and evaluate its potential for de-noising applications.","PeriodicalId":268341,"journal":{"name":"OCEANS 2006 - Asia Pacific","volume":"73 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131397946","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of River Discharge on Bay of Bengal Circulation","authors":"S. Chamarthi, A. Rao","doi":"10.1080/01490410802265476","DOIUrl":"https://doi.org/10.1080/01490410802265476","url":null,"abstract":"The bay of Bengal circulation is modeled using three-dimensional Princeton ocean model (POM). Along the coastal boundaries a higher resolution is accomplished using the curvilinear orthogonal grid. With a free-surface, terrain following sigma coordinates is used with fine resolution near the surface and bottom. The initial climatological salinity and temperature fields for the model are derived from the Levitus 94: World Ocean Atlas. The Model is forced w ith wind-stress derived from satellite information of UWM/COADS (a product of Department of Geosciences of the University of Wisconsin-Milwaukee and the National Oceanographic Data Centre/NOAA of the COADS). Bilinear interpolation is used to obtain the initial fields and wind stress to the required model specification. Using the monthly fields and wind stress the model is integrated for simulating bay of Bengal circulation. The numerical simulations on climatological scale for monsoon months were conducted to study the evolution of dynamics. The simulations bring out not only the typical characteristic features of fresh water plumes along the coast, but also intensification of the flow over the monsoon period. Also the increase in the fresh water flow was found to affect only the western parts of the bay of Bengal. The opposing currents due to monsoon winds and southward flowing fresh water discharge were also delineated.","PeriodicalId":268341,"journal":{"name":"OCEANS 2006 - Asia Pacific","volume":"67 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133599946","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Optimized Gait Generation for Anguilliform Motion","authors":"O. Parodi, L. Lapierre, B. Jouvencel","doi":"10.1109/OCEANSAP.2006.4393885","DOIUrl":"https://doi.org/10.1109/OCEANSAP.2006.4393885","url":null,"abstract":"In this paper, we are looking for a solution to optimize the path generation of an eel-like robot. Previous works have shown that a successful approach to generate path is to control explicitly the local system curvature. This control design based on Lyapunov methods warrants the convergence of the system shape towards the desired curvature profile. Then the purpose of this work is to determine a local optimized couple of curvature parameters which are able to guarantee a fast system response, an efficient propulsion which minimizes the spent energy or both of them. This is made through three criteria which are able to give us a local solution. Finally, we present results from simulations in motion planning for a ten-link-eellike robot, to illustrate the performance of the proposed solution.","PeriodicalId":268341,"journal":{"name":"OCEANS 2006 - Asia Pacific","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133760836","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multipath Virtual Sink Architecture for Underwater Sensor Networks","authors":"W. Seah, H. Tan","doi":"10.1109/OCEANSAP.2006.4393933","DOIUrl":"https://doi.org/10.1109/OCEANSAP.2006.4393933","url":null,"abstract":"The salient features of acoustic communications render many schemes that have been designed for terrestrial sensor networks unusable underwater. We therefore propose a novel virtual sink architecture for underwater sensor networks that aims to achieve robustness and energy efficiency under harsh underwater channel conditions. To overcome the long propagation delay and adverse link conditions in such environments, we make use of multipath data delivery. While conventional multipath routing tends to lead to contention near the sink, we avoid this caveat with the virtual sink design involving a group of spatially diverse physical sinks. Hence, we are able to exploit the reliability achieved from redundancy provided by multipath data delivery while mitigating the contention between the nodes.","PeriodicalId":268341,"journal":{"name":"OCEANS 2006 - Asia Pacific","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115221123","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Time Trends of Persistent Organic Pollutants in the Atmosphere over the Indian Ocean in the last 30 Years","authors":"O. Wurl, J. Potter, C. Durville, J. Obbard","doi":"10.1109/OCEANSAP.2006.4393954","DOIUrl":"https://doi.org/10.1109/OCEANSAP.2006.4393954","url":null,"abstract":"An expedition around the Indian ocean by sailboat (Jocara Indian ocean quest) in 2004/5 provided a novel and unusual opportunity to collect air samples for the analysis of persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs). The region of the Indian Ocean, and its bordering countries are considered to be a prime source of the global atmospheric POPs. Concentrations of the industrial compounds PCBs were in the range of 6.8 to 114.3 pg m-3. Hexachlorocyclohexane (HCH) and dichlorodiphenyl-trichloroethane (DDT) were the dominant OCPs and concentrations ranged between 2.4 and 105.6 pg m-3, and between 2.5 and 33.2 pg m-3 respectively. Data were compared with those reported for the mid-1970's and beginning of the 1990's to identify temporal trends in atmospheric POP levels over Southeast Asia and the Indian ocean data comparision shows that concentrations of OCPs have declined significantly, by a magnitude of two, since the mid 1970's, but were highest at the beginning of the 1990s. The trend of atmospheric PCBs is less apparent.","PeriodicalId":268341,"journal":{"name":"OCEANS 2006 - Asia Pacific","volume":"99 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123683507","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Real-Time Coded OFDM Acoustic Modem in Very Shallow Underwater Communications","authors":"Z. Kun, Quek Swee Sen, Koh Tiong Aik, Tan Bien Aik","doi":"10.1109/OCEANSAP.2006.4393961","DOIUrl":"https://doi.org/10.1109/OCEANSAP.2006.4393961","url":null,"abstract":"In this paper, we describe the design and implementation of a high-rate modem for use in very-shallow water communications. The modem employs an orthogonal-frequency-division-multiplexing (OFDM) scheme with a powerful forward error-correcting code (FEC) -turbo block code. Bit error rate (BER) measurements obtained from coastal sea trials showed that this modem is capable of delivering good error rate performance for information rates of up to nearly 10 kbits/s at transmission distances below 1700 m.","PeriodicalId":268341,"journal":{"name":"OCEANS 2006 - Asia Pacific","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114079114","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}