Browsing by Author "Hermand, J.-P."
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- Acoustic sensing techniques for the shallow water environment: inversion methods and experimentsPublication . Caiti, A.; Chapman, Ross; Hermand, J.-P.; Jesus, S. M.This volume contains the collection of papers from the second workshop on Experimental Acoustic Inversion Techniques for Exploration of the Shallow Water Environment. The workshop theme followed the original concept of the first workshop, held in Carvoeiro, Portugal, in 1999, i.e., to focus on experiments and experimental techniques for acoustic sensing in the shallow ocean. More than forty leading international scientists were invited to meet in the picturesque town of St. Angelo on the island of Ischia, in June 2004, to discuss progress in the application of new experimental techniques for exploration and assessment of shallow water environments. Acoustic techniques provide the most effective means for remote sensing of ocean and sea floor processes, and for probing the structure beneath the sea floor. No other energy propagates as efficiently in the ocean: radio waves and visible light are severely limited in range because the ocean is a highly conductive medium. However, sound from breaking waves and coastal shipping can be heard throughout the ocean, and marine mammals communicate acoustically over basin scale distances.
- AOB - Acoustic Oceanographic Buoy: concept and feasibilityPublication . Jesus, S. M.; Soares, C.; Silva, A.; Hermand, J.-P.; Coelho, E.The AOB - Acoustic Oceanographic Buoy is the single node of a network of “smart” buoys for acoustic surveillance, 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, underwater 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.
- AOB - an easily deployable, reconfigurable and multifunctional acoustic-oceanographic systemPublication . Jesus, S. M.; Soares, C.; Silva, A.; Hermand, J.-P.; Coelho, E.The concept of an easy to use and easy to deploy ocean acoustic tomographic OAT system is presented. The system is composed of a network of buoys and a data inversion online processor. This study concerns the individual node of that network—the acoustic-oceanographic buoy AOB —the data inversion technique and the testing of the system at sea. The AOB is a lightweight surface buoy with a vertical array of acoustic and temperature sensors to be hand deployed in a free-drifting configuration from a small boat. The data are locally stored and transmitted online to a remote station for processing and monitoring. Data inversion is based on a broadband matched-field tomography technique where known and unknown parameters are simultaneously searched for focalization . In situ recorded temperature data serve for algorithm initialization and calibration. The AOB was successfully deployed in several consecutive days during two rapid environmental assessment sea trials in 2003 Mediterranean and 2004 Atlantic . Data collected at sea also show that the AOB can be reconfigured as a receiving array for underwater coherent communications in the band up to 15 kHz.
- A buoy network system for acoustic monitoringPublication . Jesus, S. M.; Hermand, J.-P.; Legac, J. C.Continuous evolution of both methodologies and required technologies for REA; support of sea-based operations as demonstrated through MREA-BP-RADAR acoustic/oceanic model integration; spatially coherent processed buoys/sparse arraysinclude adaptive geoacoustic estimation
- 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.