Consulta: subjectFacets:"Backscatter"
Registros recuperados: 13
Data/hora: 29/05/2024 07:24:35

High-resolution mapping of large gas emitting mud volcanoes on the Egyptian continental margin (Nile Deep Sea Fan) by AUV surveys
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Dupre, Stephanie; Buffet, G.; Mascle, J.; Foucher, Jean-paul; Gauger, S.; Boetius, A.; Marfia, Christian.
Two highly active mud volcanoes located in 990-1,265 m water depths were mapped on the northern Egyptian continental slope during the BIONIL expedition of R/V Meteor in October 2006. High-resolution swath bathymetry and backscatter imagery were acquired with an autonomous underwater vehicle (AUV)-mounted multibeam echosounder, operating at a frequency of 200 kHz. Data allowed for the construction of similar to 1 m pixel bathymetry and backscatter maps. The newly produced maps provide details of the seabed morphology and texture, and insights into the formation of the two mud volcanoes. They also contain key indicators on the distribution of seepage and its tectonic control. The acquisition of high-resolution seafloor bathymetry and acoustic imagery maps...
Tipo: Text
Palavras-chave: Eastern Mediterranean; Seafloor morphology; Backscatter; Bathymetry; AUV; Nile Deep Sea Fan; Mud volcanoes.
Ano: 2008
URL: http://archimer.ifremer.fr/doc/2008/publication-6395.pdf

Multi-scale seafloor mapping of active seep-related structures, offshore Egypt
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Dupre, Stéphanie; Woodside, John; Klaucke, Ingo; Mascle, Jean; Foucher, Jean-paul.
The Nile deep sea fan system presents a rich variety of fluid escape structures, gas chimneys, pockmarks and carbonate crust mounds, brines pools, and several types of mud volcano. These seep-related structures were explored for the first time with the Nautile submersible during the 2003 Nautinil expedition and are characterized by high thermal gradients and highly gas-saturated sediments. More recently, high resolution side scan sonar data acquired during the 2004 Mimes expedition brings more detail to the geophysical imagery. The EdgeTech DTS-1 deep tow sonar coupled with a 2-8 kHz chirp subbottom penetrator was deployed around 100 m above the seafloor and operated at a frequency of 75 kHz. Several gas plumes were acoustically detected in the water...
Tipo: Text
Palavras-chave: Free gas emission; Backscatter; Authigenic carbonate crust; Mud volcanism; Gas chimneys; Nile Deep Sea Fan.
Ano: 2006
URL: http://archimer.ifremer.fr/doc/2005/acte-6396.pdf

Widespread active seepage activity on the Nile Deep Sea Fan (offshore Egypt) revealed by high-definition geophysical imagery
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Dupre, Stephanie; Woodside, John; Klaucke, Ingo; Mascle, Jean; Foucher, Jean-paul.
Fluid escape structures on the Nile Deep Sea Fan were investigated during the MEDIFLUX MIMES expedition in 2004. Mud volcanoes, pockmarks and authigenic carbonate structures were surveyed for the first time with a high-resolution deep-towed 75 kHz sidescan sonar and a 2-8 kHz Chirp sediment echosounder. In combination with existing multibeam bathymetry and detailed seafloor in situ geological observations, these new data allowed detailed seep analyses. About 60 gas flares were detected acoustically in the water column from the sidescan sonar raw data at water depths from 770 to 1700 m. These gas flares coincide at the seabed with 1) the centres of the mud volcanoes where mud is also extruded, 2) the borders of the mud volcanoes where the emitted gases...
Tipo: Text
Palavras-chave: Nile Deep Sea Fan; Seepage; Backscatter; Sidescan sonar; High-resolution; Gas chimneys; Mud volcanoes; Authigenic carbonates.
Ano: 2010
URL: http://archimer.ifremer.fr/doc/00013/12457/9766.pdf

Fluid Seepage in Relation to Seabed Deformation on the Central Nile Deep-Sea Fan, Part 1: Evidence from Sidescan Sonar Data
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Dano, Alexandre; Praeg, Daniel; Migeon, Sebastien; Augustin, Jean-marie; Ceramicola, Silvia; Ketzer, Joao Marcelo; Augustin, Adolfo Herbert; Ducassou, Emmanuelle; Mascle, Jean.
The central Nile Deep-Sea Fan contains a broad area of seabed destabilisation in association with fluid seepage: slope-parallel sediment undulations are associated with multibeam high-backscatter patches (HBPs) related to authigenic carbonates. During the 2011 APINIL campaign, a deep-towed sidescan and profiling system (SAR) was used to acquire high-resolution data along three transects across water depths of 1,700-2,650 m. Three seabed domains are distinguished, all developed within stratified sediments overlying mass-transport deposits (MTDs). Upslope of the undulations (&lt;1,950 m), sidescan HBPs record focused fluid seepage via seabed cracks. In the western area of undulations, sidescan HBPs are distinct from intermediate-backscatter patches (IBPs)...
Tipo: Text
Palavras-chave: Fluid seepage; Sediment deformation; Backscatter; Gas flares.
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00226/33752/37059.pdf

Fluid seepage in relation to seabed deformation on the central Nile Deep-Sea Fan, part 2: evidence from multibeam and sidescan imagery
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Praeg, Daniel; Ketzer, Joao Marcelo; Augustin, Adolfo Herbert; Migeon, Sebastien; Ceramicola, Silvia; Dano, Alexandre; Ducassou, Emmanuelle; Dupre, Stephanie; Mascle, Jean; Rodrigues, Luiz Frederico.
On the central Nile deep-sea fan, stratified sediments overlying mass-transport deposits (MTDs) are deformed into slope-parallel seabed undulations associated with fluid seepage. The western part of this system, in water depths of 1,950–2,250 m, is examined using multi-frequency data from hull-mounted and deep-towed swath/profiling systems. Sub-bottom profiles show sub-vertical fluid pipes that terminate both at and below seabed, and gas signatures along fault planes bounding the undulations. Fluid seepage is recorded by high- to intermediate-backscatter patches (HBPs, IBPs) that differ in appearance on multibeam imagery (30 kHz, ≤3 m penetration) and sidescan swaths (170/190 kHz, &lt;0.1 m penetration). Comparison of the two suggests a distinction of (a)...
Tipo: Text
Palavras-chave: Slope undulations; Fluid seeps; Backscatter; Carbonates; Pipes; Faults.
Ano: 2014
URL: http://archimer.ifremer.fr/doc/00158/26956/25251.pdf

Low-Frequency Sea Surface Radar Doppler Echo
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Yurovsky, Yury Yu.; Kudryavtsev, Vladimir N.; Grodsky, Semyon A.; Chapron, Bertrand.
The sea surface normalized radar backscatter cross-section (NRCS) and Doppler velocity (DV) exhibit energy at low frequencies (LF) below the surface wave peak. These NRCS and DV variations are coherent and thus may produce a bias in the DV averaged over large footprints, which is important for interpretation of Doppler scatterometer measurements. To understand the origin of LF variations, the platform-borne Ka-band radar measurements with well-pronounced LF variations at frequencies below wave peak (0.19 Hz) are analyzed. These data show that the LF NRCS is coherent with wind speed at 21 m height while the LF DV is not. The NRCS-wind correlation is significant only at frequencies below 0.01 Hz indicating either differences between near-surface wind...
Tipo: Text
Palavras-chave: Radar; Ocean; Backscatter; Doppler shift; Wave groups; Non-linearity; Modulation.
Ano: 2018
URL: http://archimer.ifremer.fr/doc/00445/55646/57298.pdf

ACTION RECOPLA - Inventaire et bancarisation des données de Géosciences Marines pour les façades Atlantique, Manche et Méditerranée
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Gautier, Emeric; Kerjean, Mathieu; Satra Le Bris, Catherine; Bourillet, Jean-francois.
This report presents the inventory work realized for all the Marine Geoscience dept data acquired on the French continental shelf. It lists the bathymetric, seismic and backscattering data acquired, processed and interpreted in English Channel, Atlantic and Mediterranean. All the maps used for this inventory are available within the GIS "Manche Atlantique" and "Golfe du Lion".
Tipo: Text
Palavras-chave: Inventaire; SIG; Manche; Atlantique; Méditerranée; Bathymétrie; Imagerie acoustique; Sismique; Données brutes; Traitées; Interprétées; GeoBIS; Inventory; GIS; Englsih Channel; Atlantic; Mediterranean Sea; Backscatter; Seismic; Raw; Processed; Interpreted data; GeoBIS.
Ano: 2010
URL: http://archimer.ifremer.fr/doc/00014/12558/9426.pdf

Backscattering from buried sediment layers: The equivalent input backscattering strength model
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Guillon, Laurent; Lurton, Xavier.
Signals received by low-frequency multibeam echosounders are strongly affected by sound penetration inside the upper sediment layers and by backscattering from buried layers down to depths of a few meters; this may lead to serious ambiguities and misinterpretations of experimental data. These phenomena are modeled here using a concept of equivalent input backscattering strength (EIBS), based on a combination of classical models of local backscattering strength and propagation inside fluid layered media. The local backscattering strength at a buried interface is expressed first to account for the impedance adaptation due to the overlying layers, for the angular refraction effects due to the velocity profile, and for the layered structure of the underlying...
Tipo: Text
Palavras-chave: Sound propagation; Sediment structure; Multibeam sonar; Echosounding; Backscatter; Acoustic properties; Sediment properties.
Ano: 2001
URL: http://archimer.ifremer.fr/doc/2001/publication-729.pdf

Shifts in Phytoplankton Community Structure Across an Anticyclonic Eddy Revealed From High Spectral Resolution Lidar Scattering Measurements
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Schulien, Jennifer A.; Della Penna, Alice; Gaube, Peter; Chase, Alison P.; Haëntjens, Nils; Graff, Jason R.; Hair, Johnathan W.; Hostetler, Chris A.; Scarino, Amy Jo; Boss, Emmanuel S.; Karp-boss, Lee; Behrenfeld, Michael J.
Changes in airborne high spectral resolution lidar (HSRL) measurements of scattering, depolarization, and attenuation coincided with a shift in phytoplankton community composition across an anticyclonic eddy in the North Atlantic. We normalized the total depolarization ratio (δ) by the particulate backscattering coefficient (bbp) to account for the covariance in δ and bbp that has been attributed to multiple scattering. A 15% increase in δ/bbp inside the eddy coincided with decreased phytoplankton biomass and a shift to smaller and more elongated phytoplankton cells. Taxonomic changes (reduced dinoflagellate relative abundance inside the eddy) were also observed. The δ signal is thus potentially most sensitive to changes in phytoplankton shape because...
Tipo: Text
Palavras-chave: HSRL; Depolarization; Backscatter; Phytoplankton community composition; Eddy.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00641/75313/75809.pdf

Quantitative characterisation of seafloor substrate and bedforms using advanced processing of multibeam backscatter-Application to Cook Strait, New Zealand
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Lamarche, Geoffroy; Lurton, Xavier; Verdier, Anne-laure; Augustin, Jean-marie.
A comprehensive EM300 multibeam echo-sounder dataset acquired from Cook Strait, New Zealand, is used to develop a regional-scale objective characterisation of the seafloor. Sediment samples and high-resolution seismic data are used for ground-truthing. SonarScope (R) software is used to process the data, including signal corrections from sensor bias, specular reflection compensation and speckle noise filtering aiming at attenuating the effects of recording equipment, seafloor topography, and water column. The processing is completed by correlating a quantitative description (the Generic Seafloor Acoustic Backscatter-GSAB model) with the backscatter data. The calibrated Backscattering Strength (BS) is used to provide information on the physical...
Tipo: Text
Palavras-chave: Backscatter; Multibeam echo-sounder; Sediment waves; Habitat mapping.
Ano: 2011
URL: http://archimer.ifremer.fr/doc/00031/14260/11552.pdf

Insights into the Short-Term Tidal Variability of Multibeam Backscatter from Field Experiments on Different Seafloor Types
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Montereale-gavazzi, Giacomo; Roche, Marc; Degrendele, Koen; Lurton, Xavier; Terseleer, Nathan; Baeye, Matthias; Francken, Frederic; Van Lancker, Vera.
Three experiments were conducted in the Belgian part of the North Sea to investigate short-term variation in seafloor backscatter strength (BS) obtained with multibeam echosounders (MBES). Measurements were acquired on predominantly gravelly (offshore) and sandy and muddy (nearshore) areas. Kongsberg EM3002 and EM2040 dual MBES were used to carry out repeated 300-kHz backscatter measurements over tidal cycles (similar to 13 h). Measurements were analysed in complement to an array of ground-truth variables on sediment and current nature and dynamics. Seafloor and water-column sampling was used, as well as benthic landers equipped with different oceanographic sensors. Both angular response (AR) and mosaicked BS were derived. Results point at the high...
Tipo: Text
Palavras-chave: Multibeam echosounder; Seafloor; Backscatter; Monitoring; Short-term variability; Sensitivity; High-frequency.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00485/59637/62660.pdf

The use of multibeam backscatter and bathymetry as a means of identifying faunal assemblages in a deep-sea cold seep
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Sen, Arunima; Ondreas, Helene; Gaillot, Arnaud; Marcon, Yann; Augustin, Jean-marie; Olu, Karine.
Deep-sea ecosystems have attracted considerable commercial interest in recent years because of their potential to sustain a diverse range of mankind's industrial needs. If these systems are to be preserved or exploited in a sustainable manner, mapping habitats and species distributions is critical. As biodiversity at cold-seeps or other deep-sea ecosystems is driven by habitat heterogeneity, imagery is the obvious choice for characterizing these systems and has indeed proven extremely valuable towards mapping biogenic habitats formed by dense aggregations of large sized species, such as coral reefs, tubeworm bushes or bivalve beds. However, the acquisition of detailed images with resolution sufficient for reliable identification is extremely time...
Tipo: Text
Palavras-chave: Mapping; Cold seeps; Multibeam; Bathymetry; Backscatter; Biogenic habitats.
Ano: 2016
URL: http://archimer.ifremer.fr/doc/00312/42286/41612.pdf

Sea Surface Ka-Band Doppler Measurements: Analysis and Model Development
Provedor de dados: Institutional Archive of Ifreme (ArchiMer)
Autores: Yurovsky, Yury; Kudryavtsev, Vladimir; Grodsky, Semyon; Chapron, Bertrand.
Multi-year field measurements of sea surface Ka-band dual-co-polarized (vertical transmit–receive polarization (VV) and horizontal transmit–receive polarization (HH)) radar Doppler characteristics from an oceanographic platform in the Black Sea are presented. The Doppler centroid (DC) estimated using the first moment of 5 min averaged spectrum, corrected for measured sea surface current, ranges between 0 and ≈1 m/s for incidence angles increasing from 0 to 70∘ . Besides the known wind-to-radar azimuth dependence, the DC can also depend on wind-to-dominant wave direction. For co-aligned wind and waves, a negative crosswind DC residual is found, ≈−0.1 m/s, at ≈20 ∘ incidence angle, becoming negligible at ≈ 60 ∘ , and raising to, ≈+0.5 m/s, at 70∘ . For our...
Tipo: Text
Palavras-chave: Radar; Scatterometer; Ocean; Backscatter; Doppler shift; Doppler centroid; Sea surface current; Wind drift; Modulation; Transfer function; Empirical model.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00489/60077/63399.pdf