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- 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.
- 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.
- Automatic acoustic target detection and classification off the Coast of PortugalPublication . Sabara, Razi; Soares, Cristiano; Zabel, Friedrich; Valente de Oliveira, José; Jesus, SergioOcean noise has been a topic of research for many years, for its impact in sonar detection, underwater communications and ocean acoustic observation in general. Recently, ocean sound has been designated as an Essential Ocean Variable (EOV) and is therefore, becoming increasingly recorded and monitored, along with other oceanic and meteorological variables. The research projects EMSO-PT and SUBECO aim at deploying ocean observatories along the coast of Portugal for long term ocean variables monitoring, among which ocean sound. Unlike other ocean variables, ocean sound allows for feature detection, characterisation and possibly identification with known patterns. This work shows the results obtained with current machine learning algorithms for feature detection and extraction on a two days recording of ocean noise obtained on a offshore buoy deployed under the SUBECO project, on the west coast of Portugal. Preliminary results show the possibility of improved event detection, followed by classification and clustering, that foresee a rapid and accurate analysis of large observatory acquired acoustic data sets.
- Shipping noise predictions from AIS in the Faial-Pico area, Azores archipelagoPublication . Soares, Cristiano; Duarte, Ricardo; Zabel, Friedrich; Silva, Monica A.; Jesus, SergioThe Azores archipelago, lying on the North Atlantic (NA) ocean, hosts one of the greatest diversities of cetaceans, and is an important habitat for several resident and migratory species. However, this unique diversity may be at risk due to the ocean noise generated by increasing commercial and recreational vessel traffic in the area. AIS shipping distribution and water column variability, together with suitable numerical propagation models were used to generate noise level maps for the area around Faial-Pico-Sao Jorge Islands, during June 2018. The generated noise level time-space distribution generally agrees with detected environmental variability and known navigation in the area, namely ferries between islands and fishing patterns.
- 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.