High Frequency Field Measurements of an Undular Bore Using a 2D LiDAR Scanner

Martins, Kévin; Bonneton, Philippe; Frappart, Frédéric; Detandt, Guillaume; Bonneton, Natalie; Blenkinsopp, Christopher

doi:10.3390/rs9050462

Cited by 17 publications

(20 citation statements)

References 17 publications

(33 reference statements)

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“…The largest

μ

values, which coincide with the highest

⟨ ζ^{2} ⟩

, correspond to the boundary between the outer surf zone and the shoaling region, where the largest waves first break. The scatter observed in Figure can be explained by the slight intertidal variations in wave conditions observed during the 2 days considered here (Martins, Blenkinsopp, Power, et al, ) as well as by the natural variation of

Q_{b}

in natural surf zones (Stringari & Power, ).…”

Section: Methodsmentioning

confidence: 72%

“…As mentioned above, lidar scanners (mostly in the infrared spectrum) are capable of directly measuring the free surface and are thus very powerful tools to study surf zone waves. The scanners can be stationed near the shoreline (Brodie et al, ; O’Dea et al, ) or mounted on structures such as temporary towers (Martins et al, ) or jetties (Martins, Blenkinsopp, Power, et al, ; Harry et al, ). Two‐dimensional lidars provide highly resolved, direct measurements of wave profiles which, as opposed to single‐point sensors, allow the determination of geometric information about the wave shape, and its cross‐shore evolution (Martins et al, ).…”

Section: In Situ Methods For Characterizing Non‐hydrostatic Wave Procmentioning

confidence: 99%

“…The present study uses lidar and pressure data collected during the field experiments performed at Saltburn by the Sea, UK (Figure a), during April 2016 (Martins, Blenkinsopp, Power, et al, ; Martins et al, ). Similar to Martins, Blenkinsopp, Power, et al () and Martins et al (), we only use data from 9–10 April 2016, corresponding to a swell event characterized by a peak wave period

T_{normalp} = 9 - 11

s and a significant wave height

H_{normals} = 1

m. During these two days, a mean peak wave direction of 16.9°NE was measured at the nearshore buoy deployed in 17‐m depth, with a directional spread of 15.3°. Since the coastline around the pier is oriented toward 18°NE, incident waves were essentially propagating shore normal and parallel to the pier.…”

Section: Methodsmentioning

confidence: 99%

“…This was accomplished by visually estimating

Q_{b}

, the fraction of breaking and broken waves at the ADV location from the lidar data. Following Martins, Blenkinsopp, Power, et al (), waves were considered breaking at the ADV location only when the first features associated with breaking processes (e.g., splashes and active wave face) could already be detected at that position. The results of this detection are presented in Figure , in which we can observe a linear trend between

Q_{b}

and

⟨ ζ^{2} ⟩

, the surface elevation variance measured by the lidar.…”

Section: Methodsmentioning

confidence: 99%

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Non‐hydrostatic, Non‐linear Processes in the Surf Zone

et al. 2020

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In the surf zone, non‐hydrostatic processes are either neglected or estimated using linear wave theory. The recent development of technologies capable of directly measuring the free surface elevation, such as 2‐D lidar scanners, allow for a thorough assessment of the validity of such hypotheses. In this study, we use subsurface pressure and lidar data to study the non‐linear and non‐hydrostatic character of surf zone waves. Non‐hydrostatic effects are found important everywhere in the surf zone (from the outer to the inner surf zones). Surface elevation variance, skewness, and asymmetry estimated from the hydrostatic reconstruction are found to significantly underestimate the values obtained from the lidar data. At the wave‐by‐wave scale, this is explained by the underestimation of the wave crest maximal elevations, even in the inner surf zone, where the wave profile around the broken wave face is smoothed. The classic transfer function based on linear wave theory brings only marginal improvements in this regard, compared to the hydrostatic reconstruction. A recently developed non‐linear weakly dispersive reconstruction is found to consistently outperform the hydrostatic or classic transfer function reconstructions over the entire surf zone, with relative errors on the surface elevation variance and skewness around 5% on average. In both the outer and inner surf zones, this method correctly reproduces the steep front of breaking and broken waves and their individual wave height to within 10%. The performance of this irrotational method supports the hypothesis that the flow under broken waves is dominated by irrotational motions.

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“…The largest

μ

values, which coincide with the highest

⟨ ζ^{2} ⟩

Q_{b}

in natural surf zones (Stringari & Power, ).…”

Section: Methodsmentioning

confidence: 72%

Section: In Situ Methods For Characterizing Non‐hydrostatic Wave Procmentioning

confidence: 99%

T_{normalp} = 9 - 11

s and a significant wave height

H_{normals} = 1

Section: Methodsmentioning

confidence: 99%

“…This was accomplished by visually estimating

Q_{b}

Q_{b}

and

⟨ ζ^{2} ⟩

, the surface elevation variance measured by the lidar.…”

Section: Methodsmentioning

confidence: 99%

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Non‐hydrostatic, Non‐linear Processes in the Surf Zone

et al. 2020

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“…[Madsen et al(2008)], [Tissier et al(2011)] and [Bonneton et al(2015)]). In that case the hydrostatic assumption is no longer valid (see [Martins et al(2017)]).…”

Section: Introductionmentioning

confidence: 99%

Recovering water wave elevation from pressure measurements

Bonneton

Lannes

2017

J. Fluid Mech.

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The reconstruction of water wave elevation from bottom pressure measurements is an important issue for coastal applications, but corresponds to a difficult mathematical problem. In this paper we present the derivation of a method which allows the elevation reconstruction of water waves in intermediate and shallow waters. From comparisons with numerical Euler solutions and wave-tank experiments we show that our nonlinear method provides much better results of the surface elevation reconstruction compared to the linear transfer function approach commonly used in coastal applications. More specifically, our method accurately reproduces the peaked and skewed shape of nonlinear wave fields. Therefore, it is particularly relevant for applications on extreme waves and wave-induced sediment transport. R e −iωt u(t, X)dt.We also denote by f (D) Fourier multipliers in space, and g(D t ) Fourier multipliers in time, defined as f (D)u(t, ·)(ξ) = f (ξ) u(t, ξ) and g(D t )u(·, X)(ω) = g(ω) u(ω, X). Physical background.We consider three-dimensional waves propagating in intermediate and shallow water depths. We denote z = ζ(t, X) the elevation of the free surface above the still water level z = 0, and by z = −h b (X) the bottom elevation. We are looking for a relationship between pressure time series measured at the bottom, P b (t, X 0 ), and the elevation ζ(t, X 0 ) at the same horizontal location X 0 .

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