Abstract: The AcousticOceanographicBuoy (AOB) is a light acoustic receiving device that is being developed in the framework of a joint research project and tested during the Maritime Rapid Environmental Assessment (MREA) sea trials. One of the AOB’s application is in Matched-Field Tomography (MFT) when a reduced number of receivers is available in opposition to traditional systems used in tomography. One problem of chief importance in MFT is the degree of uniqueness of the problem’s solution which is highly dependent on the number of receivers and on the number of free parameters. This paper studies the possibility of using matched-field processors with reduced ambiguity levels in comparison to conventional processors with application to acoustic data collected during the MREA sea trials. Two aspects are investigated: (a) the choice of an explicit broadband data model, where the exploitation of the spectral coherence of the acoustic field is seen as a mean to reduce the ambiguity level of the cost function used in the optimization; (b) conventional and high-resolution methods based on the proposed broadband model are implemented and compared.
Abstract— The AOB - AcousticOceanographicBuoy is the single node of a network of “smart” buoys for acoustic surveil- lance, Rapid Environmental Assessment (REA) and underwater communications. The AOB is a lightweight surface buoy with a vertical array of acoustic receivers and temperature sensors to be air dropped or hand deployed from a small boat. The received data is geotime and GPS precisely marked, locally stored and processed by on board dedicated DSP hardware. AOBs can exchange data over a local area network that includes submerged, sea surface (like for instance other AOBs) and air or land located nodes, allowing for the integration of all users in a seamless network. Specific software allows AOB usage in complex tasks such as passive or multistatic acoustic surveillance, acoustic observations for REA oceanographic forecast and model calibration, bottom and water column acoustic inversion, un- derwater communications and cooperating target tracking. The AOB was successfully deployed in several consecutive days during two Maritime REA sea trials in 2003 (Mediterranean), in 2004 (Atlantic) and for an high-frequency underwater communications experiment during MakaiEX, 2005 (Hawai). Data collected at sea shows that the AOB is a versatile, robust and easy to use tool for a variety of broadband underwater acoustic applications.
The AcousticOceanographicBuoy (AOB) telemetry system wants to meet the 'advanced' sonobuoy characteristics. It integrates the air RaN by using a standard 'IEEE 802.11' WLAN configuration, and the underwater AcN by using a hydrophone array and an acoustic source. The first AOB prototype was tested during the Maritime Rapid Environmental Assessment sea trials in 2003 , and in 2004 . The present version of the AOB was tested, from 15th of September to 2nd of October 2005, during the MakaiEx sea trial off Kauai Island, Hawaii, USA, in the context of the High Frequency Initiative promoted by HLS Research Inc, San Diego, USA.
It is now well accepted in the underwater acoustic scientific community that below, say, 1 kHz acoustic propagation models are accurate enough to be able to predict the received acoustic field up to the point of allowing precise and reliable source tracking in range and depth with only limited environmental information. This results from a large number of studies both theoretical and with real data, carried out in the last 20 years. With the event of underwater communications and the necessity to increase the signal bandwidth for allowing higher communication rates, the frequency band of interest was raised to above 10 kHz. In this frequency band the detailed knowledge of the environment - acoustic signal interplay is reduced. The purpose of the MakaiEx sea trial is to acquire data in a complete range of frequencies from 500 Hz up to 50 kHz, for a variety of applications ranging from high-frequency tomography, coherent SISO and MIMO applications, vector - sensor, active and passive sonar, etc...The MakaiEx sea trial, that took place off Kauai I. from 15 September - 2 October, involved a large number of teams both from government and international laboratories, universities and private companies, from various countries. Each team focused on its specific set of objectives in relation with its equipment or scientific interest. The team from the University of Algarve (UALg) focused on the data acquired by their receiving AcousticOceanographicBuoy - version 2 (AOB2) during six deployments in the period 15 - 27 September. This report describes the AOB2 data set as well as all the related environmental and geometrical data relative to the AOB2 deployments. The material described herein represents a valuable data set for supporting the research objectives of projects NUACE 1 , namely to fulfill NUACE’s task 3 and 4 and
An important item to be tested during the MREA'03 sea trial was the AOB computer code to online control, monitor and invert the data collected with the AOB. In this prelim- inary test the software was separated in two parts: the sonobuoy control and monitoring and the online data inversion. The sonobuoy control and monitoring was performed by a specially developed Windows OS oriented program running on a laptop. This computer was tted with a PCMCIA wireless card attached to an omnidirectional 12 dBi outdoor antenna via a 1 W amplier. This computer code was performing two main tasks: one was to get the GPS location of the buoy and follow its drift in absolute coordinates from which the test area bathymetry was retrieved using archival data of the area. The second task was to monitor the data being acquired via a specialized program interacting with the buoy PC via Windows message passing protocol, over the wireless network. It was also possible to transfer acoustic data via ftp for on board online inversion. That data was shared on the network to a multiprocessor host devoted to data inversion. To carry out the data inversion in nearly real-time, a Dual AMD firstname.lastname@example.org GHz CPU rackmount computer running Linux was used.
From the above, the three-dimensional (3D) temperature mapping of a given area assumes a crucial importance. Even sampling the area with various instruments, the assessment methods must resort to interpolation of the measured quantities, due to the inherent sparsity of practical ocean casts. Considering the significant complexity of ocean processes in coastal areas, it is more realistic to perform a statistical instead of a deterministic interpolation. The departing point is to treat temperature as a random variable with statistical second order models. The parameters of these models are estimated from the data acquired along time and space. Then, it is possible to compute the interpolated 3D temperature field, and predict its short-time evolution. The interpolation methods have been based on the estimation theory known as objective analysis, first described in an oceanographic context by Bretherton et al., and is now an important tool in oceanography for both analysis and observational array design. In the past, it was current practice to assume oceanographic fields as stationary, homogeneous and isotropic. Carter and Robinson have introduced time dependence and horizontal anisotropy in the fields. Elisseeff and Schmidt have considered anisotropy also in depth .
During June 23, 2003 a series of communication codes were transmitted to probe the underwater acoustic channel capabilities for data communication. The scope of the pro- cessing is to use the virtual time reversal concept as presented in [10, 11]. Very simply speaking, the idea is to use the received probe signal as an image of the signal pulse shape convolved with the channel impulse response to matched-filter the received data sequence that follows the probe signal. In doing this, there is the hope that the acous- tic channel is sufficiently stable to hold during the data sequence duration, which is 16 seconds in our case. Figure 4.13(a) shows the module of the baseband signal recovered from the matched-filtering (virtual time reversing) of the data sequence of code B, for hy- drophones 1, 2 and 3. It can be seen that for all three hydrophones the pulse shape peak is clearly extracted with a much better reconstruction of the data following data packet with hydrophones 2 and 3 than with hydrophone 1, due to the low signal to noise ratio. Figure 4.13(b) shows the coherent summation of the signals of plots (a). The theoretical
laboratory, in terms of underwater acoustic signal processing techniques, and has faced a significant technological development in the last years, in terms of acoustic emission and reception systems. Included in the latter is the AcousticOceanographicBuoy, a drifting system with data storage capabilities, whose feasibility in ocean acoustic sensing has been demonstrated, for example, in the MREA’03 and ’04, and RADAR’07 sea trials. Special thanks are due to Emanuel Ferreira-Coelho. He gave me an important input on oceanography, and explanations regarding the oceanographic forecasts used in the present work, when accepting me as a visiting student. Last but not least, I address warm hugs to my parents and my friends, specially Helga Hampton, my graduation colleagues, Paula Coelho, Barbara Nicolas, Julien Huillery, Anna Zabel, Cl´ audio Lima, Ana Bela, Fernando Marin, and, last but not least, my beloved wife, Usa Vilaipornsawai, for continuous and unconditional encouragement. To all the above, an ocean-wide THANK YOU!!!
The CALCOM’10 experiment took place off the southern coast of Portugal, about 12nm southeast of Vilamoura, from 22nd to 24th June 2010 -Fig.1 (a). The data analyzed herein was acquired on 24th June along the continental steep slope to the deeper ocean, Fig. 1(b). The probe signals were transmitted by a Lubell LL-1424 sound source installed on a towfish, Fig 2(a). The source was towed along the track represented by a dotted line in Fig 1(b). The signals were acquired by a 16-hydrophone AcousticOceanographicBuoy (AOB22, Fig 2(b)) deployed in a free drifting mode at the location represented by the star A2d in Fig. 1(b). The AOB22 drift is represented by the thick black line, where the star A2r indicates the location of the buoy recovery. Probe signals for field calibration were emitted during the periods are represented by green lines, labelled from P1 to P6 according to their sequence in time. The positioning information is given by the GPS installed in the buoy and on the boat.
The frequency spectrum is calculated every 30 minutes by an internal microprocessor using the amount of raw data obtained in this time interval and it is immediately transmitted to the land base. The raw and spectral data transmission is done every hour through a radio antenna positioned at the top of the waverider buoy. The radio operation frequency is between 25.5 and 35.5 MHz. The equipment records one vertical displacement (elevation) and two horizontal displacements (north and west). In this way, the variance, kurtosis and asymmetry are computed. The collected data visualization can be done in real time in 2D and 3D formats through the W@ves21 (W21) software, developed by Datawell. This software analyses, processes and presents the data recorded by the equipment. For the real-time data display, the W@ves21 program needs to be connected to the rfBouy module. Thus, the waverider buoy can be monitored by any computer. The signiicant wave height is calculated through the W@ves21 (W21) software by performing the zero-crossing analysis, which uses the average of 1/3 of the highest wave heights (DATAWELL BV, 2006).
Underwater Acoustic Sensor Network (UASN): A collection of sensor nodes which communicates among them through the emerging underwater acoustic communication technology is known as UASN. Acoustic communication technology is the best choice when compare to the radio waves and optical waves that is why it was chosen for the communication in underwater. Underwater acoustic network gaining attention due to their importance in underwater applications for military and commercial purpose.
acoustic reflex threshold reduction does not depend on the frequency of the facilitating stimulus. They were able to observe threshold reductions at various frequencies (500 Hz, 1, 2, 4 and 6 kHz), suggesting that the cochlea tonoto- pic pattern does not interfere in the process. The detected independence from frequency indicates that acoustic reflex facilitation is not primarily mediated by afferent mecha- nisms. The authors propose that facilitation takes place at the efferent portion of the acoustic reflex arc.
Resonant frequencies of the combustion chamber were identiied by analyzing the registered FRF (from 0 to 5,000 Hz), which were measured along the cavity of the chamber. Once identiied, these frequencies were compared with the respective values, calculated theoretically (Table 2). As for each coniguration, the theoretical frequencies were known, an experimental procedure of frequencies separation was performed by observing its value proximity (close to those calculated) and the higher amplitude (also considering the transversal/axial position of the microphone). Then, for each coniguration, the acquired FRF were analyzed and the average of the frequencies and magnitudes was evaluated, by using the transversal and axial measurements, in order to obtain the set of resonant frequencies of the referred cavity. Such a way, with the theoretical versus experimental comparison, one can have an idea of the inherent acoustic mode shapes in the cavity, associated with the resonance frequencies.
measurements have potential advantages over tympanom- etry, particularly in children. First, ear canal pressurization is not necessary, and thus there is no distortion in the canal. Second, the measures are performed over a range of frequencies, instead of a single frequency eval- uated in tympanometry. And finally, the measures can be quickly obtained. Therefore, it is possible that the acoustic reflectance measurements can provide more information,
Incoherent systems for underwater communication have been researched since the early 1970s, but there have been no fundamental improvements since the introduction of diversity techniques (Sec. 2.3.3). Instead, the evolution of computing power and hardware has led to the use of larger symbol constellations and higher rates. The simple implementation characteristics of incoherent FSK on both transmitter and receiver, together with its reliability under harsh channel conditions, promoted its continued use in offshore equipment, control downlinks for AUVs, and telemetry uplinks for oceanographic sensors , applications where data rates are not significant compared to the power consumption, processing power, and reliability requirements. Recent research has focused on the practical implementation details of FSK, from interoperability  to chip area  and the applicability to underwater sensor networks .
104 Fado singers participated on this study: 47 males, 57 females; 90 amateur and 14 professional, with ages from [18–67]. Fado singers produced spoken tasks consisting on sustained [a,i,u,s,z] plus reading aloud and sung tasks consisting on sustained [a,i,u] of the song “Nem ´as paredes confesso”. Acoustic voice parameters were compared between males vs. females, professionals vs. amateurs and young vs. older voices a two independent t-test with an α at .05.
attain relatively modest data rates. Instead, coherent commu- nication aims at an efficient exploitation of the frequency band and assumes a time-continuous data stream with fully symbol coherence. The problem becomes then the time and Doppler spreading of the underwater acoustic channel due to the boundary interaction and due to ocean inherent variability. The concept in UAN is to go behind P2P to a network topology where multiple nodes would allow to sample the environment to a point where there would be almost always a route for an information packet to reach from any point A to B. Since in practice the required network density is seldom satisfied, the communicating route may be achieved by moving the nodes within the network to positions that are reachable, communication wyse. Therefore, the UAN network will have a variable geometry integrating fixed and mobile nodes allowing for some degree of environmental adaptivity according to the predicted communication performance given apriori environmental conditions.
It is noteworthy that the comparisons using OSCAR currents were not significant for showing a rheotactic response. While this might be compelling evidence to counter the proposed finding, we feel the most likely explanation for the weaker patterns in the OSCAR analysis is that it is the only ocean current product not providing a daily estimate, as OSCAR is a 5-day composite dataset due to the geometry of satellite orbital cycles and altimeter/ scatterometer swath widths. It is difficult to measure animal behavior cued to the environment if the environmental measure is an average over 5 days, while the behavior is measured over the course of a single day. Given the daily NOAA drifter buoy analysis showed evidence of rheotaxis, and that the OSCAR data is essentially tuned to NOAA drifter buoy movement, we feel the lack of significant finding in the OSCAR analysis does not in any way preclude existence of positive rheotaxis in oceanic juvenile loggerhead turtles. The consistent finding in all 3 strata of HYCOM currents (with the HYCOM shallow arguably the most suitable estimate) remains strong evidence of positive rheotaxis.
Altogether nineteen listeners with an above average aptitude for music or acoustics, acquainted with the liturgy in a wor- ship space were chosen and trained for the subjective acous- tic tests. Some of the listeners had to be audiometrically tested (250 Hz – 8 kHz) to ascertain their hearing conditions. The locations of the music sources (MA and MB) and listen- ers seating for the subjective acoustic tests in Our Lady of Divine Providence Church are shown in Figure 3.
complex shorelines. Currently the large wave buoys utilising accelerometers to mea- sure the pitch, heave and roll of the buoy are considered highly reliably instruments for operational measurements. Nevertheless, there also exists several different technolo- gies that use a GPS-receiver to measure the displacement of the wave buoy, which have all been proven to be sufficiently accurate in a majority of situations (Herbers