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Acoustic Seafloor - Crossref

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Last Updated: 03 May 2022

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Performance of Seismic Observation by Distributed Acoustic Sensing Technology Using a Seafloor Cable Off Sanriku, Japan

Applying a DAS sensor to the seafloor cable is highly cost-effective in a marine area since the number of data can be significantly increased. The Earthquake Research Institute, the University of Tokyo, in 1996, a seafloor seismic tsunami monitoring cable system using an optical fiber for data transmission was installed off the coast of Sanriku. Using the phase data from the DAS survey, the arrivals of P- and S-waves of the earthquake with a magnitude of 3 were evidently visible. We compared results from the DAS test with those from the seismometer because there are conventional seismometers in Sanriku's cable system. The noise levels of the DAS measurement were determined, and there was no temporal variation of the noise levels. A seismic investigation using the DAS system and airguns was conducted in November 2020, and the DAS system accurately recorded signals from the airguns.

Source link: https://doi.org/10.3389/fmars.2022.844506


A Multi-Frequency Acoustic Investigation of Seafloor Methane Seep Sites at Omakere Ridge, Hikurangi Margin, New Zealand

The Hikurangi Margin, east of the North Island of New Zealand's south, is an anticlinal thrust ridge with water depths of 1100–1700mon, and it is a region of active seafloor methane seepage associated with a large gas hydrate province. Localised buildups of authigenic carbonate and chemosynthetic seep fauna on a seafloor that is otherwise defined by soft, muddy sediments, providing a rare glimpse into the gas hydrate system's workings. Three recently-acquired acoustic datasets on Omakere Ridge have been successfully photographed; a P-CableTM high-resolution 3D seismic reflection database; a multibeam sonar backscatter registry; and a ParasoundTM subbottom profiler dataset ; and a ParasoundTM subbottom profiler dataset ; and a ParasoundTM subbottom profiler dataset. Since correcting for beam pattern effects and angular variation in backscatter after taking into account the bathymetry, Sonar backscatter mosaics were created. At five seep sites on Omakere Ridge, three-dimensional seismic attributes, multibeam backscatter intensity, and shallow subsurface reflection characteristics all provide new insight into the previously unknown extent of authigenic carbonate build-ups, methane migration pathways, and seep formation mechanisms. Carbonate deposits of at least 6–7 meters thickness and high multibeam backscatter density are expected in areas where the carbonates are less developed, according to areas with low seismic reflection coefficient and moderate/high sonar backscatter intensity.

Source link: https://doi.org/10.26686/wgtn.17000113.v1


A Multi-Frequency Acoustic Investigation of Seafloor Methane Seep Sites at Omakere Ridge, Hikurangi Margin, New Zealand

The Hikurangi Margin, east of the North Island of New Zealand, is an active seafloor methane hydrate province with a large gas hydrate province. Localised buildups of authigenic carbonate and chemosynthetic seep fauna on a seafloor that has otherwise been defined by soft, muddy sediments, giving a unique window into the gas hydrate system's workings. Sites on Omakere Ridge have been successfully photographed using three recently acquired acoustic datasets: a P-CableTM high-resolution 3D seismic reflection database; a multibeam sonar backscatter registry; and a ParasoundTM subbottom profiler database. After correcting for beam pattern effects and angular difference in backscatter after taking into account the bathymetry, Sonar backscatter mosaics were created. At five seep sites on Omakere Ridge, a comparison of 3D seismic attributes, multibeam backscatter intensity, and shallow subsurface reflection methods provides new insight into the previously unknown extent of authigenic carbonate buildups, methane migration pathways, and seep initiation mechanisms. Carbonate formations of at least 6–7 m thickness are estimated as carbonate deposits with low seismic reflection coefficient and moderate/high sonar backscatter fidelity in areas where the carbonates are less developed, according to areas with low seismic reflection coefficient and moderate/high backscatter intensity.

Source link: https://doi.org/10.26686/wgtn.17000113


Applying a Multi-Method Framework to Analyze the Multispectral Acoustic Response of the Seafloor

New marine geological and benthic biological research has been prompted by advances to acoustic seafloor mapping devices. Multibeam echosounders have become a common device for acoustic remote sensing of the seabed. We investigate the possibility of seabed discrimination based on multispectral backscatter results within a multi-method framework here. We present a new MBES survey obtained near the Doce River mouth, which is located on the eastern Brazilian continental shelf. This approach yielded an efficient way to synthesize these results spatially to determine two specific acoustic seabed classes, with four subclasses within one of the larger classes that closely matched seafloor sediment samples collected at the site. The analysis found that the integration of image-based and angular range analysis techniques with multispectral MBES results would yield significant benefits for seafloor characterization and mapping.

Source link: https://doi.org/10.3389/frsen.2022.860282


Applying a multi-method framework to analyze the multispectral acoustic response of the seafloor

Novel benthic geological and biological research has been prompted by advances to acoustic seafloor mapping systems. Multibeam echosounders have become a common tool for acoustic remote sensing of the seabed, and more recently, multispectral MBES backscatter has been introduced to characterize the seabed in greater detail, but methods for using this data are still being investigated. Here, we investigate the likelihood for seabed discrimination based on multispectral backscatter results within a multi-method framework. We present a new MBES survey obtained using four operating frequencies near the Doce River mouth, which is located on the eastern Brazilian continental shelf. For the majority of muddy areas, the median uncalibrated backscatter values from the mosaics were low. The angular response curve in these regions shows significant backscatter level loss, with a more pronounced backscatter level loss in the higher frequency. Also, the multifrequency acoustic data provided greater differentiation of muddy and fine sand sediments in this area than coarser sediments. Backscatter data has been investigated in various ways within the context of seafloor classification, including: visual interpretation of mosaics, textural analysis, image-based analysis, and angular range estimation. Several novel supervised and unsupervised methods have been used in seabed classification, including various clustering methods. Further research into the discrimination ability of multispectral backscatter and comparison of clustering methods may help determine the application of these techniques for mapping seabed sediments.

Source link: https://doi.org/10.5194/egusphere-egu22-12128


How to detect slow slip and long-term seafloor deformation? Lessons from two acoustic ranging campaigns on the submerged flank of Mt Etna

The installation of seafloor geodetic systems to accurately monitor fault displacement and strain accumulation in the last decade has greatly enhanced our understanding of seafloor deformation and offshore dangers in the recent decade. Mount Etna's Southeast flank slides seawards at a rate of 3 cm/yrs, according to On-land geodetic networks. The first acoustic ranging measurements between 2016 and 2018 revealed offshore active deformation and seafloor displacement by detecting a st-event of up to 4 cm with a right-lateral offset. We therefore performed our second acoustic geodetic deployment at the same site offshore Mount Etna between September 2020 and November 2021, using a new network architecture. Our findings show that the direct-path acoustic ranging technique is well-suited to detect various forms of fault slip at faults with solid surface traces.

Source link: https://doi.org/10.5194/egusphere-egu22-9770


GNSS/Acoustic positioning of acoustic beacons on the seafloor using an autonomous surface vehicle. Example from the FOCUS experiment offshore Sicily (Italy)

Using laser reflectometry, the European Research Council's FOCUS project, which is funded by the European Research Council, aims at monitoring deformation across a flooded submarine fault with an optical fiber. A network of eight seafloor geodetic stations was deployed on both directions of the cable and fault to calibrate the measured strains in an absolute reference frame, such as the International Terrestrial Reference Frame. We use a GNSS/Acoustic positioning system to locate the acoustic beacons related to the ITRF. It's a challenge to locate acoustic beacons on the seafloor within 1 cm by GNSS/A. The lever arm between the GNSS and acoustic antennas on the surface platform must be precisely identified; the platform's movement must be precisely tracked. Then, in addition to reducing the uncertainty in GNSS positioning, an acquisition policy must be developed to minimize the uncertainties in the acoustic ranging results, due to the unknown sound-speed field in the water column and its variability during the ranging sessions. We positioned the ASV relative to several beacons at once and tested various trajectories: quasi-static stations of the ASV at the barycenter of 3 beacons, or a series of straight profiles equidistant to pair of beacons. In addition, when the ASV was gathering GNSS/A records, a number of vertical temperature/pressure/salinity profiles was obtained from the support vessel to track changes in the sound-speed. Then the acoustic range data can be combined with the sound-speed data to find the beacon barycenter, providing a minimum-squares inversion.

Source link: https://doi.org/10.5194/egusphere-egu22-3758


Overview of the seafloor geodetic observation conducted by the Japan Coast Guard using the GNSS-Acoustic ranging combination technique

The Japanese Islands lie in subduction zones where the Pacific Plate and the Philippine Sea Plate subduct, making the islands one of the world's most seismically active zones. One of the government branches that carry out geodetic studies to advance megathrust earthquake study is the Hydrographic and Oceanographic Department of the Japan Coast Guard. GNSS-A's ability allows us to determine the global coordinates of a seafloor reference point in precision of centimeters by simultaneously completing GNSS monitoring of a sea surface platform and trilateration of seafloor benchmarks using acoustic ranging. The Seafloor Geodetic Observation Array Array, as of now, is on display at 27 seafloor sites along the Japan Trench and Nankai Trough, as well as the Nankai Trough.

Source link: https://doi.org/10.5194/egusphere-egu22-1652


The COSMUS Expedition: Seafloor Images and acoustic bathymetric data from the PS124 expedition to the southern Weddell Sea, Antarctica

RV Polarstern, the research icebreaker, carried out an extensive multidisciplinary study expedition across Antarctica's southern Weddell Sea, between February 3rd and March 2021. The Ocean Floor Observation and Bathymetry System was used 20 times during the Continental Shelf Multidisciplinary Flux Study expedition to gather high resolution seafloor image and acoustic data with a 26-megapixel resolution camera, HD video camera, forward facing acoustic camera, and multibeam side-scan system from heights of between 1. 5 and 4. 5 meters above the seafloor. We have provided the complete image dataset set from various deployments, as well as raw side-scan results, and estimated high resolution bathymetric maps derived from this acoustic data after the cruise. http://doi. pangaea. com/PANGAEA. 939341, forward facing acoustic camera data at www. doi. pangaea. de/10. 1594/PANGAEA. 939341.

Source link: https://doi.org/10.5194/essd-2021-444


Detailed S-Wave Velocity Structure of Sediment and Crust off Sanriku, Japan by a New Analysis Method for Distributed Acoustic Sensing Data Using a Seafloor Cable with Seismic Interferometry

To eliminate DAS instrument noise and effectively remove surface waves from short-time data, we first applied a frequency-wavenumber filter to the DAS data. For each subarray, the estimated phase velocities of the fundamental- and first higher-mode Rayleigh waves were then used to determine one-dimensional V s structures. Our new analysis system, which utilizes seismic interferometry to marine DAS results, will broaden the horizons for determining heterogeneous V s and V p/ V s structures of sediment layers and upper crusts in subduction zones. These results show that adding both frequency-wavenumber filtering and seismic interferometry to marine DAS data can be a new tool for determining the heterogeneous V s and V p/ V s structure of sediment layers and the upper crust in subduction zones.

Source link: https://doi.org/10.21203/rs.3.rs-1371937/v1

* Please keep in mind that all text is summarized by machine, we do not bear any responsibility, and you should always check original source before taking any actions

* Please keep in mind that all text is summarized by machine, we do not bear any responsibility, and you should always check original source before taking any actions