Sediment interval velocities from a monostatic multibeam sonar

Common‐depth‐point seismic reflection data were generated on a computer using simple ray tracing and analyzed with processing techniques currently used on actual field recordings. Constant velocity layers with curved interfaces were used to simulate complex geologic shapes. Two models were chosen to illustrate problems caused by curved geologic interfaces, i.e., interfaces at depths which vary laterally in a nonlinear fashion and produce large spatial variations in the apparent stacking velocity. A three‐layer model with a deep structure and no weathering was used as a control model. For comparison, a low velocity weathering layer also of variable thickness was inserted near the surface of the control model. The low velocity layer was thicker than the ordinary thin weathering layers where state‐of‐the‐art static correction methods work well. Traveltime, moveout, apparent rms velocities, and interval velocities were calculated for both models. The weathering introduces errors into the rms velocities and traveltimes. A method is described to compensate for these errors. A static correction applied to the traveltimes reduced the fluctuation of apparent rms velocities. Values for the thick weathering layer model were “over corrected” so that synclines (anticlines) replaced false anticlines (synclines) for both near‐surface and deep zones. It is concluded that computer modeling is a useful tool for analyzing specific problems of processing CDP seismic data such as errors in velocity estimates produced by large lateral variations in overburden.

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Smart Ocean: A New Fast Deconvolved Beamforming Algorithm for Multibeam Sonar

Sensors ◽

10.3390/s18114013 ◽

2018 ◽

Vol 18 (11) ◽

pp. 4013 ◽

Cited By ~ 2

Author(s):

Jie Huang ◽

Tian Zhou ◽

Weidong Du ◽

Jiajun Shen ◽

Wanyuan Zhang

Keyword(s):

High Frequency ◽

Real Data ◽

Side Lobe ◽

Tunnel Effect ◽

Computation Complexity ◽

Acoustic Image ◽

Multibeam Sonar ◽

Sonar System ◽

Topographic Survey ◽

Beamforming Algorithm

A new fast deconvolved beamforming algorithm is proposed in this paper, and it can greatly reduce the computation complexity of the original Richardson–Lucy (R–L algorithm) deconvolution algorithm by utilizing the convolution theorem and the fast Fourier transform technique. This algorithm makes it possible for real-time high-resolution beamforming in a multibeam sonar system. This paper applies the new fast deconvolved beamforming algorithm to a high-frequency multibeam sonar system to obtain a high bearing resolution and low side lobe. In the sounding mode, it restrains the tunnel effect and makes the topographic survey more accurate. In the 2D acoustic image mode, it can obtain clear images, more details, and can better distinguish two close targets. Detailed implementation methods of the fast deconvolved beamforming are given, its computational complexity is analyzed, and its performance is evaluated with simulated and real data.

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Observations of Shallow Methane Bubble Emissions From Cascadia Margin

Frontiers in Earth Science ◽

10.3389/feart.2021.613234 ◽

2021 ◽

Vol 9 ◽

Author(s):

Anna P. M. Michel ◽

Victoria L. Preston ◽

Kristen E. Fauria ◽

David P. Nicholson

Keyword(s):

Water Column ◽

Water Depth ◽

Dissolved Methane ◽

Multibeam Sonar ◽

Surface Ocean ◽

Transient Nature ◽

Technological Approach ◽

Open Questions ◽

Cascadia Margin ◽

Methane Bubble

Open questions exist about whether methane emitted from active seafloor seeps reaches the surface ocean to be subsequently ventilated to the atmosphere. Water depth variability, coupled with the transient nature of methane bubble plumes, adds complexity to examining these questions. Little data exist which trace methane transport from release at a seep into the water column. Here, we demonstrate a coupled technological approach for examining methane transport, combining multibeam sonar, a field-portable laser-based spectrometer, and the ChemYak, a robotic surface kayak, at two shallow (<75 m depth) seep sites on the Cascadia Margin. We demonstrate the presence of elevated methane (above the methane equilibration concentration with the atmosphere) throughout the water column. We observe areas of elevated dissolved methane at the surface, suggesting that at these shallow seep sites, methane is reaching the air-sea interface and is being emitted to the atmosphere.

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