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- Development of a high-power multilayer PVDF acoustic projector for 40 to 80 kHz bandPublication . Silva, António; Hughes, Ashley; Pozzatti, Daniel; Zabel, Friedrich; Viegas, Rúben; Martins, MarcosA piston type projector using the PVDF piezoelectric polymer was developed for operating in underwater environment, below 100 kHz. For those frequencies PZT piezoelectric ceramic is usually a preferable choice and PVDF is only considered for frequencies above a few hundreds of kHz. This paper will show that efficient underwater acoustic projectors for frequencies below 100 kHz can be implemented regarding an appropriate impedance adapter is being used. The developed project presents a calibrated transmitting voltage response (TVR) of approximately 166, 160 and 175 dB at 40, 50 and 75 kHz, respectively. The PVDF TVR values are compatible with the PZT projectors available on market with the advantage of having a larger bandwidth than most PZT projectors. To the authors knowledge this is the first time that a PVDF projector attain such characteristics. Although theoretically the PVDF projector bandwidth is larger than 40 to 80 kHz, in practice it was observed that only between those frequencies the project presents a stable operation for the transmission of long-term signals.
- Acoustic oceanographic buoy data report Makai Ex 2005Publication . Jesus, S. M.; Silva, A.; Zabel, F.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 Acoustic Oceanographic Buoy - 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 NUACE1, namely to fulfill NUACE’s task 3 and 4 and RADAR2, namely its tasks 2 and 3 devoted to the developement and testing of a field of sonobuoys.
- RBR thermistors array for AOB2Publication . Zabel, F.; Martins, C.This report describes an electronic circuit board for interfacing the RBR thermistor chain manufactured by Richard Bracker Research, Ontario (Canada), with the Acoustic Oceanographic Buoy (version 2) - AOB2. The interface consists on a set of bridge amplifiers and associated electronics for converting the NTC thermistor signals into temperature related values in the data acquisition CPU control of the AOB2. With this board the temperature measured along the RBR thermistor chain array can be monitored on real time together with the acoustic data via the wireless lan network to which the AOB2 is associated.
- The TV-APM interface: a web service for collaborative modelingPublication . Rodríguez, O. C.; Silva, A.; Zabel, F.; Jesus, S. M.Current development of Internet access, together with available zero-cost Open Source applications (like, for instance, PHP, Python, etc.) can be integrated in order to minimize the constrains induced by the geographical separation of international centers, which collaborate in a given project. The advantage of such approach lies in the sharing of common analysis methods, without particular constrains to specific directions of analysis. The discussion presented in this paper describes the Time Variable Acoustic Propagation Model (TV-APM) web interface, which was created as a collaborative service of acoustic modeling for the participants of the PHITOM and UAN projects. This paper describes the general architecture of the interface, its current shortcomings and advantages, and presents a set of modeling results for short range acoustic propagation, which accounts for source–array and sea surface motion.
- Using active and passive acoustics to assess O2 production of a Posidonia oceanica meadowPublication . Felisberto, P.; Zabel, F.; Rodríguez, O. C.; Santos, P.; Jesus, S. M.; Champenois, W.; Borges, A. V.; Santos, RuiThis work discusses the data acquired during two experiments conducted in October 2011 and May 2013 in the Bay of la Revellata, Calvi, Corsica for the purpose of developing an acoustic system for monitoring the oxygen production of a seagrass meadow.
- The TV-APM interface: a web service for collaborative modellingPublication . Rodríguez, Orlando; Silva, António J.; Zabel, Friedrich; Jesus, S. M.Current development of Internet access, together with available zero-cost Open Source applications (like, for instance, PHP, Python, etc.) can be integrated in order to minimize the constrains induced by the geographical separation of international centers, which collaborate in a given project. The advantage of such approach lies in the sharing of common analysis methods, without particular constrains to specific directions of analysis. The discussion presented in this paper describes the Time Variable Acoustic Propagation Model (TV-APM) web interface, which was created as a collaborative service of acoustic modeling for the participants of the PHITOM and UAN projects. This paper describes the general architecture of the interface, its current shortcomings and advantages, and presents a set of modeling results for short range acoustic propagation, which accounts for source–array and sea surface motion.
- Correlation between the acoustic noise field measured in a Posidonia oceanica bed and the photosynthetic activityPublication . Felisberto, P.; Zabel, F.; Rodríguez, O. C.; Santos, P.; Jesus, S. M.; Champenois, W.; Borges, A. V.; Santos, RuiDuring the period of one week, from May 8 to 15, 2013, acoustic data was gathered at three locations over a Posidonia oceanica bed in the Bay of Revellata, Corsica. Preliminary analysis of the acoustic data shows that the environmental noise field in the band 2-7kHz was dominant during the period. The noise in this band is generally associated with wind and surface agitation. However, the noise power was not significantly correlated with wind speed. On the contrary, the diel cycle of the noise power at three locations was highly correlated with the water column concentration of O2, as measured by optodes. These measurements of environmental noise have confirmed the correlation between active acoustic signals transmitted along a seagrass meadow and the photosynthetic activity of the plants observed in a previous experiment conducted in the same area .The results suggest that acoustic noise can be used as a proxy for the photosynthetic oxygen production of a Posidonia oceanica meadow. Therefore, this work is a contribution for the development of a low cost passive acoustic system to assess the primary production of coastal ecosystems .
- Linking acoustic communications and network performance. Integration and experimentation of an underwater acoustic networkPublication . Caiti, A.; Grythe, K.; Hovem, J. M.; Jesus, S. M.; Lie, A.; Munafò, Andrea; Reinen, Tor Arne; Silva, A.; Zabel, F.Underwater acoustic networks (UANs) are an emerging technology for a number of oceanic applications, ranging from oceanographic data collection to surveillance applications. However, their reliable usage in the field is still an open research problem, due to the challenges posed by the oceanic environment. The UAN project, a European-Union-funded initiative, moved along these lines, and it was one of the first cases of successful deployment of a mobile underwater sensor network integrated within a wide-area network, which included above water and underwater sensors. This contribution, together with a description of the underwater network, aims at evaluating the communication performance, and correlating the variation of the acoustic channel to the behavior of the entire network stack. Results are given based on the data collected during the UAN11 (May 2011, Trondheim Fjord area, Norway) sea trial. During the experimental activities, the network was in operation for five continuous days and was composed of up to four Fixed NOdes (FNOs), two autonomous underwater vehicles (AUVs), and one mobile node mounted on the supporting research vessel. Results from the experimentation at sea are reported in terms of channel impulse response (CIR) and signal-to-interference-plus-noise ratio (SINR) as measured by the acoustic modems during the sea tests. The performance of the upper network levels is measured in terms of round trip time (RTT) and probability of packet loss (PL). The analysis shows how the communication performance was dominated by variations in signal-to-noise ratio, and how this impacted the behavior of the whole network. Qualitative explanation of communication performance variations can be accounted, at least in the UAN11 experiment, by standard computation of the CIR and transmission loss estimate.
- TRA - Transmit Receive Array (project plan version 2)Publication . Zabel, F.; Martins, C.; Jesus, S. M.; Silva, A.This report describes an update to the project plan for the development of a Transmit Receive Array (TRA). This system is under development for the Underwater Acoustic Barriers (UAB) project which aims at studying, developing and testing in the field the concept of building an underwater acoustic barrier for detecting intruders in a given area.
- The acoustic oceanographic buoy. A light acoustic data acquisition systemPublication . Soares, C.; Zabel, F.; Martins, C.; Silva, A.; Jesus, S. M.The Acoustic Oceanographic Buoy (AOB) is a light acoustic receiving device that incorporates acoustic and non-acoustic signals received in various channels along a vertical line array that provide oceanographic and environment measurements all of which are uniquely GPS time referenced. The physical characteristics of the AOB, in terms of size, weight and autonomy, will tend to those of a standard sonobuoy with, however, the capabilities: of local data storage, dedicated signal-processing, GPS self localizing, real-time monitoring and online data transmission.