Loading...
8 results
Search Results
Now showing 1 - 8 of 8
- On the performance of geo-acoustic estimation for a distributed sensor arrayPublication . Jesus, Sergio; Mantouka, A.; Felisberto, Paulo; Soares, CristianoThe vision underlying the Widely scalable Mobile Underwater Sonar Technology (WiMUST) project is that of developing advanced cooperative and networked control / navigation systems to enable a large number (tenths) of marine robots towing small acoustic arrays to act as a coordinated team for seismic sub-bottom imaging. The space-time coherent processing of bottom returns requires the ensemble of short acoustic arrays to be seen as a single spatially distributed sensor array. Since the vehicles are free to move along range, cross-range and depth the resulting distributed sensor array may take, at least conceptually, any spatial shape. With array shape freedom comes the question of which is the most suitable (or optimal) array geometry for sub-bottom imaging and inversion. The answer to this question hinges, among others, on the definition of performance of a seismic sub-bottom profiling system. Determining the optimal sensor array geometry is clearly a ill-posed problem, since the optimal geometry is itself bottom dependent, and there is no such environment as "one size fits all". This work addresses several criteria for sub-bottom profiling system performance including gain, resolution and probability of detection. Two physical models will be tested: one based on acoustic wave reflection used in traditional seismic imaging, and another normally used in matched-field bottom properties estimation, that includes propagation and refraction. Simulations to support the theoretical developments and algorithms were obtained on a scenario inspired in a real environment off the coast of Peljesac (Croatia).
- Shipping noise field calibration via source inversionPublication . Jesus, Sergio; Soares, Cristiano; Zabel, FriedrichThere is significant evidence that the low-frequency mean acoustic noise pressure level in the ocean has been constantly increasing in the last decades. The main noise sources responsible for this increase were identified as ship traffic, offshore construction and oil & gas surveying. The Portuguese Navy funded SUBECO project aims at deploying a network of multiparametric offshore buoys for environmental and acoustic monitoring. A preferred location for the individual buoys is within or close by the ship traffic separation lanes along the west coast of Portugal. It is therefore expected that the received acoustic field will be dominated by shipping noise as a mixture of both short and long range ships. Most ships will have an AIS so their position may be known at all times. One of the objectives of this network is to use the recorded sound to infer and calibrate model predicted noise in a wider area. This work proposes a relatively simple technique for estimating the radiated noise level of ship tracks within acoustic reach of a single (or a small number of closely localized) hydrophone(s). It is expected that the data constrained predicted field with the estimated source levels will provide a better fit to the actual wide area acoustic field. This work is a contribution to fulfill the requirements of Portugal to the European Union Marine Strategy Framework Directive (MSFD) aiming at a good environmental status.
- On the applications of a compact autonomous acoustic recorderPublication . SOARES, CRISTIANO; Martins, Celestino; Zabel, Friedrich; Silva, A.A number of acoustic A compact acoustic recorder, primarily designed for underwater noise monitoring, is presented in this paper. The Self-Register Hydrophone has been used in several occasions during the past three years, in underwater noise monitoring activities. However, this kind of device also find application in other areas such as array processing and passive acoustic monitoring of marine mammals. An overview on the application of the Self-Register Hydrophone is given herein.
- Deployment characterization of a floatable tidal energy converter on a tidal channel, Ria Formosa, PortugalPublication . Pacheco, André; G-Gorbeña, Eduardo; Plomaritis, Haris; Garel, Erwan; Gonçalves, J. M. S.; Bentes, L.; Monteiro, P.; Afonso, Carlos; Oliveira, Frederico; Soares, C.; Zabel, F.; Sequeira, ClaudiaThis paper presents the results of a pilot experiment with an existing tidal energy converter (TEC), Evopod 1 kW floatable prototype, in a real test case scenario (Faro Channel, Ria Formosa, Portugal). A baseline marine geophysical, hydrodynamic and ecological study based on the experience collected on the test site is presented. The collected data was used to validate a hydro-morphodynamic model, allowing the selection of the installation area based on both operational and environmental constraints. Operational results related to the description of power generation capacity, energy capture area and proportion of energy flux are presented and discussed, including the failures occurring during the experimental setup. The data is now available to the scientific community and to TEC industry developers, enhancing the operational knowledge of TEC technology concerning efficiency, environmental effects, and interactions (i.e. device/environment). The results can be used by developers on the licensing process, on overcoming the commercial deployment barriers, on offering extra assurance and confidence to investors, who traditionally have seen environmental concerns as a barrier, and on providing the foundations whereupon similar deployment areas can be considered around the world for marine tidal energy extraction.
- Passive acoustics as a tool for global ocean monitoring and explorationPublication . Jesus, S. M.; Rodríguez, O. C.; Felisberto, P.; Soares, C.The ocean is vast, rich, fragile and unexplored. Despite a massive investment in the last years, ocean exploration remains localized at the ocean surface and in shallow coastal areas, covering merely 5% of the total volume. It is well known that marine life has perfectionned acoustics as its primarily sense for every day tasks such as locating preys, sensing danger, breeding, etc. So, in the ocean, sound has the same role as light on land. It is well known that sound propagates to long distances in the ocean and hence acoustics can be seen as the ONLY mean to "see" the ocean interior at a global scale, in respect of the environment and at a reasonable cost. There is nowadays scientific evidence that listening to ocean ambient sound allows to retrieve information about i) anthropogenic sound, related to man activities such as shipping, bathymetric sonar, industrial construction, echo-sounding and defence; ii) environmental related sound such as that of earthquakes, ice, rainfall, waves and wind, and iii) biological related sounds as for example, that of marine mammals, fish and the acoustic activity of invertebrates in coastal areas. Ambient sound can also be used for indirectly estimating environmental and biological quantities such as sub-bottom structure or coastal flora health and abundance. This paper presents an overview of recent results for some of those passive acoustic imaging techniques.
- Acoustic observatories for ocean tomography: geometries and multi-array Matched-Field TomographyPublication . SOARES, CRISTIANO; Felisberto, P.; Jesus, SergioThe present study proposes an MFT algorithm for directly estimating a two-dimensional range-dependent or three-dimensional temperature field. The acoustic system has multiple acoustic emitters and receiver arrays according to a given geometry. The acoustic signal is emitted from one emitter at a time, and collected at multiple receiver arrays. The MFT method is adapted to iteratively produce parameter estimates for each individual environmental cell. To accomplish this, an MF processor based on a multi-array acoustic data model is considered, in order to account for acoustic data collected simultaneously at several acoustic arrays.
- Measuring underwater noise with high endurance surface and underwater autonomous vehiclesPublication . Silva, A.; Matos, A.; Soares, C.; Alves, J. C.; Valente, J.; Zabel, F.; Cabral, H.; Abreu, N.; Cruz, N.; Almeida, R.; Ferreira, R. N.; Ijaz, S.; Lobo, V.This paper describes the results of AcousticRobot'13 - a noise measurement campaign that took place off the Portuguese Coast in May 2013, using two high endurance autonomous vehicles capable of silent operation (an underwater glider and an autonmomous sailing vessel) equipped with hydrophones, and a moored hydrophone that served as reference. We show that the autonomous vehicles used can provide useful measurements of underwater noise, and describe the main advantages and shortcomings that became evident during the campaign.
- Seismoacoustic bottom inversion with AUV towed streamers: a multi-stage approachPublication . Soares, Cristiano; Jesus, Sergio; Mantouka, Agni; Felisberto, PauloThe WiMUST (Widely scalable Mobile Underwater Sonar Technology) Project envisions using a team of autonomous underwater vehicles towing short acoustic arrays for seismic surveying of seabottom geoacoustic properties. One of the objectives in the project is to tackle the inversion of acoustic data collected with short towed horizontal arrays by means of a Matched-Field Inversion (MFI) technique. While there is great deal of experience in MFI and the so-called focalization applied to horizontal propagation scenarios, in near vertical propagation scenarios, with a source receiver horizontal distance limited to a few tens of meter or less, there is little understanding in terms of feasibility of the acoustic inversion of bottom properties. In particular, the simultaneous inversion of bottom properties (soundspeeds, densities, attenuations) of multiple bottom layers needs to be tackled, since the experimenter has to account for the admissible mismatch of other environmental properties such as water soundspeed and depth, and the potential solution ambiguity inherent to an optimization problem with ten or more unknown parameters. The actual simulation study, carried out with an environmental scenario and geometric set up based on the Peljesac data set, considers a shallow water acoustic propagation scenario with a short array. A sensitivity analysis in MFI provides understanding on the observability of the unknown parameters of interest. A mismatch analysis indicates that watercolumn mismatch (soundspeed and depth) may cause the MFI procedure to break down. Based on the conclusions taken from the sensitive and mismatch analysis, an iterative acoustic inversion concept with feedback of intermediate parameter estimates is developed and tested with simulated data.