Refraction and scattering into a sandy ocean sediment in the 30-40-kHz band

Chotiros, Nicholas P.; Smith, Eric; Piper, James N.

doi:10.1109/joe.2002.1040924

Cited by 12 publications

(9 citation statements)

References 18 publications

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“…In addition to their effect on turbulence and sediment transport processes, ripples can also play an important role in biogeochemical processes [e.g., Huettel et al ., ; Precht and Huettel , ; Rocha , ] as well as penetration of acoustic energy in the seabed [e.g., Chotiros et al ., ; Jackson et al ., ; Thorsos and Richardson , ].…”

Section: Introductionmentioning

confidence: 98%

Temporal and spatial evolution of wave‐induced ripple geometry: Regular versus irregular ripples

Nelson

Voulgaris

2014

JGR Oceans

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Concurrent observations of inner shelf near bed hydrodynamics and acoustic imagery of the seabed are used to relate wave-induced ripple geometry (wavelength and orientation) to near bed directional wave velocities. The observations were collected on the continental shelf of the South Atlantic Bight at water depths of 9.5 and 30 m off the coasts of South Carolina (median size 177 mm) and Georgia (388 mm), respectively. 2-D spectral analysis techniques are performed on the imagery to automate detection of ripple wavelength, orientation, and irregularity. Our analysis shows that ripple irregularity is a time-dependent process dependent on magnitude, direction, and duration of wave forcing. During energetic events, ripple geometry changes rapidly and the ripples align with the main wave direction. During periods of low energy, close to the critical conditions for initiation of sediment motion, ripple evolution occurs at a much slower rate often leading to irregularities such as terminations and bifurcations along the ripple crest. Under constantly changing wave direction, the rippled bed becomes highly disorganized. Six types of ripples are defined based on newly developed irregularity parameters: linear, bifurcating-linear, linear-bifurcating, bifurcating and cross, irregular, and disorganized beds. Ripple irregularity depends on the time history of the bed; ripples remain irregular until their wavelength and orientation attain a nearly equilibrium geometry. The observations collected provide significant information on the response of the seabed to wave forcing and identify processes that should be reproduced by any time-dependent ripple prediction model. Ripple irregularity can only be predicted using such timedependent models.

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Section: Introductionmentioning

confidence: 98%

Temporal and spatial evolution of wave‐induced ripple geometry: Regular versus irregular ripples

Nelson

Voulgaris

2014

JGR Oceans

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“…The state of relict ripples immediately after the transition to subcritical conditions is the initial condition for subsequent ripple degradation processes, which are often biologically controlled by a variety of burrowing organisms [ Wheatcroft , 1994]. Ripples have also recently been shown to enhance the amount of acoustic energy that penetrates into the seafloor at subcritical acoustic grazing angles [ Chotiros et al , 2002; Jackson et al , 2002]. Since the use of acoustics to detect buried objects usually occurs in subcritical conditions, the morphology of relict ripples is of first order importance to these issues.…”

Section: Introductionmentioning

confidence: 99%

Observations of wave orbital scale ripples and a nonequilibrium time‐dependent model

Traykovski¹

2007

J. Geophys. Res.

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[1] Measurements of seafloor ripples under wave-dominated conditions from the LEO15 site and the Martha's Vineyard coastal observatory were used to develop a time-dependent model for ripple geometry. The measurements consisted of backscatter imagery from rotary side-scan sonars, centimeter resolution bathymetric maps from a two-axis rotary pencil-beam sonar, and forcing hydrodynamics. During moderate energy conditions the ripple wavelength typically scaled with wave orbital diameter. In more energetic conditions the ripples reached a maximum wavelength of 0.8 to 1.2 m and did not continue to increase in wavelength or decrease in height. The observations showed that the relict ripples left after storms typically had wavelengths close to the maximum wavelength. The time-dependent model is based on an equilibrium model that allows the ripples to maintain wavelength proportional to wave orbital diameter until a suspension threshold determined by wave velocity and grain size is reached. The time-dependent model allows the ripple spectra to follow the equilibrium solution with a temporal delay that is based on the ratio of the ripple cross-sectional area to the sediment transport rate. The data was compared to the equilibrium model, a simplified version of the time-dependent model (where the ripples were assumed to follow the equilibrium model only when the bed stress was sufficient to move sediment), and the complete time-dependent model. It was found that only the complete time-dependent model was able to correctly predict the long wavelength relict ripples and that the other approaches underpredicted relict ripple wavelengths.

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“…Therefore, many recent studies have been focused on examining using sonar with sub-critical incidence at the seabed (Schmidt, 1999). In the process of improving such techniques, it has been found that the presence of sand ripples on the seafloor enhances sonar penetration into the sediment at sub-critical acoustic angles (Chotiros, et al, 2002;Jackson, et al,2002).…”

Section: Mine Detectionmentioning

confidence: 99%

Seafloor ripples created by waves from Hurricane Ivan on the west Florida shelf

Bowers¹

2006

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Recent studies have shown that the presence of sand ripples on the seabed improves sonar detection of buried mines at sub-critical angles. Sidescan sonar data of ripples off on the west Florida shelf were collected as part of ONR's Ripples Departmental Research Initiative (DRI) September 26-29 th and November 7-9 th , 2004. Hurricane Ivan, the strongest storm of the 2004 hurricane season, passed over the experiment site a week before the first data collection. This study focuses on the ripples created by Ivan. Average relict ripple wavelengths left after the storm were found to increase with water depth (50 cm, 62 cm, and 83 cm in 20, 30, and 50 meter water depths) despite the fact that orbital diameter decreases with water depth.Ripple prediction requires information about surface gravity waves and sediment grain size. The most reliable offshore wave field available was created with Wavewatch III by Naval Postgraduate School scientists. These waves were inputted into Delft3D WAVE, incorporating the nearshore wave model SWAN to predict waves at the locations where ripples were measured. Orbital motions at the seabed and grain size were inputted into a time-dependent ripple model with varying dissipation parameters to estimate sand ripples created by Hurricane Ivan. Ripple wavelength was found to be more strongly dependent on grain size than wave dissipation.

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Refraction and scattering into a sandy ocean sediment in the 30-40-kHz band

Cited by 12 publications

References 18 publications

Temporal and spatial evolution of wave‐induced ripple geometry: Regular versus irregular ripples

Temporal and spatial evolution of wave‐induced ripple geometry: Regular versus irregular ripples

Observations of wave orbital scale ripples and a nonequilibrium time‐dependent model

Seafloor ripples created by waves from Hurricane Ivan on the west Florida shelf

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