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- TRIDENT – Technology based impact assessment tool foR sustaInable, transparent Deep sEa miNing exploraTion and exploitation: A project overviewPublication . Silva, E.; Viegas, D.; Martins, A.; Almeida, J.; Almeida, C.; Neves, B.; Madureira, P.; Wheeler, A. J.; Salavasidis, G.; Phillips, A.; Schaap, A.; Murton, B.; Berry, A.; Weir, A.; Dooly, G.; Omerdic, E.; Toal, D.; Collins, P. C.; Miranda, M.; Petrioli, C.; Barrera Rodríguez, C.; Demoor, D.; Drouet, C.; Serafy, G. El; Jesus, Sergio; Dañobeitia, J.; Tegas, V.; Cusi, S.; Lopes, L.; Bodo, B.; Beguery, L.; VanDam, S.; Dumortier, J.; Neves, L.; Srivastava, V.; Dahlgren, T. G.; Thomassen Hestetun, J.; Eiras, R.; Caldeira, R.; Rossi, C.; Spearman, J.; Somoza, L.; González, F. J.; Bartolomé, R.; Bahurel, P.By creating a dependable, transparent, and cost-effective system for forecasting and ongoing environmental impact monitoring of exploration and exploitation activities in the deep sea, TRIDENT seeks to contribute to the sustainable exploitation of seabed mineral resources. In order to operate autonomously in remote locations under harsh conditions and send real-time data to authorities in charge of granting licenses and providing oversight, this system will create and integrate new technology and innovative solutions. The efficient monitoring and inspection system that will be created will abide by national and international legal frameworks. At the sea surface, mid-water, and the bottom, TRIDENT will identify all pertinent physical, chemical, geological, and biological characteristics that must be monitored. It will also look for data gaps and suggest procedures for addressing them. These are crucial actions to take in order to produce accurate indicators of excellent environmental status, statistically robust environmental baselines, and thresholds for significant impact, allowing for the standardization of methods and tools. In order to monitor environmental parameters on mining and reference areas at representative spatial and temporal scales, the project consortium will thereafter develop and test an integrated system of stationary and mobile observatory platforms outfitted with the most recent automatic sensors and samplers. The system will incorporate high-capacity data processing pipelines able to gather, transmit, process, and display monitoring data in close to real-time to facilitate prompt actions for preventing major harm to the environment. Last but not least, it will offer systemic and technological solutions for predicting probable impacts of applying the developed monitoring and mitigation techniques.
- Monitoring bubble production in a seagrass meadow using a source of opportunityPublication . Felisberto, Paulo; Rodríguez, Orlando; Silva, João P.; Jesus, Sergio; Ferreira, Hugo Q.; Ferreira, Pedro P.; Cunha, Maria E.; de los Santos, Carmen B.; Olivé, Irene; Santos, RuiUnder high irradiance, the photosynthetic activity of dense seagrass meadows saturates the water forming oxygen bubbles. The diel cycle of bubble production peaks at mid-day, following light intensity pattern. It is well known that bubbles strongly affect the acoustic propagation, increasing signal attenuation and decreasing the effective water sound speed, noticeable at low frequencies. Thus, the diurnal variability of bubbles may show an interference pattern in the spectrograms of low frequency acoustic signals. In an experiment conducted in July 2016 at the Aquaculture Research Station of the Portuguese Institute for the Sea and Atmosphere in Olhão, Portugal, the spectrograms of low frequency (<20kHz) broadband noise produced by water pumps in a pond of 0.48ha covered by the seagrass Cymodocea nodosa showed interference patterns that can be ascribed to the variability of the sound speed in the water. Preliminary analysis suggests that the daily cycle of bubble concentration can be inferred from these interference patterns.
- On bottom properties estimation from towed array dataPublication . Jesus, S. M.; Jesus, M. C.Estimating seabottom structure from the analysis of acoustic returns of an explosive source (air-gun, sparker...) has been used for a long time as a routine survey technique. Recent work showed the possibility of using well-suited numerical numbers to invert the acoustic field for inverting detalied sedimental physical properties.
- Iterative range estimation in a sloping-bottom shallow-water waveguide using the generalized array invariantPublication . Cho, Chomgun; Song, H. C.; Hursky, P.; Jesus, SergioThe array invariant theory was generalized by incorporating the waveguide invariant beta, referred to as the generalized array invariant. In this paper, the generalized array invariant is extended to mildly range-dependent environments with a sloping bottom where the waveguide invariant is variable in range. Assuming knowledge of the bottom slope, the array invariant can be applied iteratively to estimate the source range starting with beta=1 (i.e., range-independent), which converges toward the correct source range by updating b at the previously estimated range. The iterative array invariant approach is demonstrated using a short-aperture vertical array (2.8-m) in a sloping-bottom shallow-water waveguide from the Random Array of Drifting Acoustic Receivers 2007 experiment, where a high-frequency source (2-3.5 kHz) close to the surface (6-m) was towed between 0.5 and 5 km in range with the water depth varying from 80 to 50 m. (C) 2017 Acoustical Society of America.
- 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.
- Shallow water tomography with a sparse array during the INTIMATE'98 sea trialPublication . Felisberto, P.; Jesus, S. M.; Stephan, Y.; Demoulin, X.Invert acoustic data using sparse arrays - at the limit with a single hydrophone - is a challenging task. The final goal is to obtain a rapid environmental assessment with systems both easier to deploy and less expensive than full vertical arrays. In this paper, it is shown that using a known broadband source signal and an array with few hydrophones, ocean acoustic tomography can be performed, even in a complex internal waves induced highly variable ocean. The inversion approach presented herein is based on an arrival matching processor and a genetic algorithm search procedure. Due to the poor accuracy on the a priori knowledge of the source range, source depth and water depth, the inversion procedure was split in two stages: in the first stage the geometric parameters where estimated and in the second stage sound speed estimates where obtained. This procedure was applied to field data, acquired during the INTIMATE'98 sea trial, in a shallow water area off the coast of France in the Gulf of Biscay. That area is expected to have a relatively high internal wave activity, specially during the summer. A 4 sec long - 700 Hz bandwidth linear frequency modulated signal was transmitted from a ship suspended sound source and received on a 4 element vertical array at a range of approximately 10.5 km, over a relatively range-independent area. The results from the inversion of the acoustic data are in line with those obtained by concurrent non acoustic data like GPS source range, measured source depth, XBT casts and temperature sensors.
- A sensitivity study for full-field inversion of geoacoustic data with a towed array in shallow waterPublication . Jesus, S. M.This paper presents some of the preliminary work aimed at estimating the ocean bottom morphological structure in coastal waters using a towed array. In order to obtain an idea of the expected performance of the system and draw some conclusions on its operation this study presents the sensitivity of three processors to variations of: array length, source and receiver positions, sensor noise, source frequency and frequency band. Conclusions tend to demonstrate that cost function sensitivity to sound speed variations is higher on the bottom top layers and it increases with array length. An increased sensitivity is generally acompanied by a cost function non-monotonic behavior creating local minima and making it more di cult to reach the global minimum. Attenuations have in general small in uence on the acoustic eld structure and are therefore di cult to estimate. Increasing the signal frequency band by incoherent module averaging has no signi cant in uence on sensitivity. A cost function relaying on the conventional matched lter has shown low sensitivity to sensor noise and is being extended to matching directional data from bottom arrivals at several frequencies. Mismatch cases, mainly those related to array/source relative position, will be also presented.
- Editorial: observing ocean soundPublication . Delory, Eric; Širovic, Ana; Jesus, SergioOcean sound is emerging as a key health indicator of marine ecosystems, increasingly at risk of anthropogenic stressors (Duarte et al., 2021). The full potential of this Essential Ocean Variable (EOV) keeps developing (Tyack, 2018). The science and methods resulting from this EOV address an increasing number of domains, from geophysics to bio- and eco-acoustics. It also offers opportunities to respond to questions as varied as geohazard and marine life occurrence, and provides potentially cost-effective solutions to monitor biodiversity and ecosystems at large.
- Medium frequency (800-1600Hz) geoacoustic inversions with drifting sparse arrays during the MREA BP07 experimentPublication . Legac, J. C.; Hermand, J.-P.; Jesus, S. M.In order to evaluate properly the acoustic propagation characteristics in shallow water environments, it is well established that appropriate knowledge of the acoustic properties of the seabottom is required. In the last decade, full-field geoacoustic inversion techniques have been demonstrated to provide adequate methodologies to assess those properties. However, several of the developed techniques may suffer a lack of adequacy to the design of low-frequency active sonar systems (LFAS) for which the assessment of seabottom characteristics are drawn. For instance most matched-field inversion techniques demonstrated so far use acoustical signals at much lower frequencies than those of the sonar (few tens to hundreds Hertz to be compared to the 1-2 kHz range of standard LFAS). Furthermore, some of the techniques may be difficult to be handled in an â€oeoperationally relevant context― since they are based on relatively complex designed systems such as highly instrumented vertical line arrays spanning the whole water column. In this paper, we investigate the potentialities of medium frequency acoustical signals (800-1600 Hz) received at several ranges (from 1 km to 10 km) along a field of drifting sparse arrays eventually reduced to a couple of hydrophones or even a single one for spatial coherent geoacoustic inversion purposes. The experimental datasets of the Maritime Rapid Environmental Assessment BP’07 seatrials South of Elba Island in the Mediterranean Sea are used to support this study.
- Geophysical seafloor exploration with a towed array in shallow waterPublication . Caiti, A.; Jesus, S. M.The quantitative measurement or estimation of the geophysical properties of the seafloor upper sedimentary strata is a requirement in several marine applications, from geotechnical engineering to underwater acoustics. Traditional methods employ in-situ instrumentation (cone penetrometers, coring, etc.) and are able to probe the seafloor at selected points. This project aims at exploring the feasibility of seafloor model identification by acoustic means. In particular, the project has considered the use of an acoustic system, in which a ship tows both an acoustic source and an horizontal array of receivers. From the acoustic field measured at the receiving array, the seafloor parameters are estimated by suitable inversion algorithms. The project focused in particular on the use of such a system in shallow waters, and considered the advantages and limitations of the method from the point of view of system requirementes, signal processing and inversion strategies. Sensitivity studies show that it is indeed possible to recover the seafloor parameters in shallow water with a moderate aperture towed array, and experimental results are shown to demonstrate the feasibility of the concept. Possible improvements and further lines of research are also discussed.