|
|
|
| Registros recuperados: 10 | |
|
| |
|
| |
|
|
| Lurton, Xavier; Eleftherakis, Dimitrios; Augustin, Jean-marie. |
| The sediment backscatter strength measured by multibeam echosounders is a key feature for seafloor mapping either qualitative (image mosaics) or quantitative (extraction of classifying features). An important phenomenon, often underestimated, is the dependence of the backscatter level on the azimuth angle imposed by the survey line directions: strong level differences at varying azimuth can be observed in case of organized roughness of the seabed, usually caused by tide currents over sandy sediments. This paper presents a number of experimental results obtained from shallow-water cruises using a 300-kHz multibeam echosounder and specially dedicated to the study of this azimuthal effect, with a specific configuration of the survey strategy involving a... |
| Tipo: Text |
Palavras-chave: Azimuth dependence; Seafloor backscatter; Multibeam echosounder; Sand ripples. |
| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00386/49782/50326.pdf |
| |
|
|
| Kan, Hironobu; Urata, Kensaku; Nagao, Masayuki; Hori, Nobuyuki; Fujita, Kazuhiko; Yokoyama, Yusuke; Nakashima, Yosuke; Ohashi, Tomoya; Goto, Kazuhisa; Suzuki, Atsushi. |
| Submerged tropical karst features were discovered in Nagura Bay on Ishigaki Island in the southern Ryukyu Islands, Japan. The coastal seafloor at depths shallower than similar to 130 m has been subjected to repeated and alternating subaerial erosion and sedimentation during periods of Quaternary sea-level lowstands. We conducted a broadband multibeam survey in the central area of Nagura Bay (1.85 x 2.7 km) and visualized the high-resolution bathymetric results over a depth range of 1.6-58.5 m. Various types of humid tropical karst landforms were found to coexist within the bay, including fluviokarst, doline karst, cockpit karst, polygonal karst, uvalas, and mega-dolines. Although these submerged karst landforms are covered by thick postglacial reef and... |
| Tipo: Text |
Palavras-chave: Submerged karst; Coral reef; Multibeam echosounder; SCUBA; Ryukyu Islands; Japan. |
| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00352/46285/45961.pdf |
| |
|
| |
|
|
| Trenkel, Verena; Berger, Laurent; Bourguignon, Sebastien; Doray, Mathieu; Fablet, Ronan; Masse, Jacques; Mazauric, Valerie; Poncelet, Cyrille; Quemener, Gael; Scalabrin, Carla; Villalobos, Hector. |
| This paper provides an overview of the progress Ifremer has made recently in fisheries acoustics and the study of small pelagic fish by: i) pushing observation frontiers using a range of platforms including an autonomous underwater vehicle, AUV, ii) developing measuring instruments and methods and iii) studying fish distributions. Presently, information from several frequencies of single-beam echosounders is routinely collected together with data from the ME70 multibeam echosounder. For onboard data acquisition control the HERMES software was developed. The new MOVIES 3D software includes modules for simultaneous realistic 3D visualisation and post-processing such as bottom detection, school extraction and calculation of descriptors and integration of all... |
| Tipo: Text |
Palavras-chave: Multibeam echosounder; Oceanographic AUV; Pelagic fish; Fisheries acoustics. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/00000/11165/7517.pdf |
| |
|
|
| Bourguignon, Sebastien; Berger, Laurent; Scalabrin, Carla; Fablet, Ronan; Mazauric, Valerie. |
| Multibeam echosounders and sonars are increasingly used in fisheries acoustics for abundance estimation. Because of reduced side-lobe levels in the beam-array pattern, the new Simrad ME70 multibeam echosounder installed on board Ifremer's RV "Thalassa" has been designed to allow improved detection of fish close to the seabed. To achieve this objective, precise and unambiguous detection of the water-bottom interface is required, which raises the issue of bottom detection, especially in the outer beams. The bottom-detection method implemented in the ME70 is based on the amplitude of the reverberated echo. Such an approach is efficient for vertical beams, but less accurate for beams with higher incidence angles, typically 30°40° for the beam configurations... |
| Tipo: Text |
Palavras-chave: Multibeam echosounder; Fisheries; Bottom detection; Acoustics. |
| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/publication-6629.pdf |
| |
|
| |
|
|
| Malik, Mashkoor; Lurton, Xavier; Mayer, Larry. |
| Multibeam echosounders (MBES) have become a widely used acoustic remote sensing tool to map and study the seafloor, providing co-located bathymetry and seafloor backscatter. Although the uncertainty associated with MBES-derived bathymetric data has been studied extensively, the question of backscatter uncertainty has been addressed only minimally and hinders the quantitative use of MBES seafloor backscatter. This paper explores approaches to identifying uncertainty sources associated with MBES-derived backscatter measurements. The major sources of uncertainty are catalogued and the magnitudes of their relative contributions to the backscatter uncertainty budget are evaluated. These major uncertainty sources include seafloor insonified area (1–3 dB),... |
| Tipo: Text |
Palavras-chave: Multibeam echosounder; Calibration; Incidence angle. |
| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00429/54018/57435.pdf |
| |
|
| |
| Registros recuperados: 10 | |
|
|
|
