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Remote Sens. 2017, 9(5), 462; doi:10.3390/rs9050462

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

1
Research Unit for Water, Environment and Infrastructure Resilience (WEIR), University of Bath, Bath BA2 7AY, UK
2
UMR EPOC (Université de Bordeaux/CNRS), Talence 33615, France
3
Géosciences Environnement Toulouse (GET), UMR 5563, CNRS/IRD/UPS, Observatoire Midi-Pyrénées (OMP), 14 Avenue Edouard Belin, Toulouse 31400, France
4
Laboratoire d’Études en Géophysique et Océanographie Spatiales (LEGOS), UMR 5566, CNRS/IRD/UPS, Observatoire Midi-Pyrénées (OMP), 14 Avenue Edouard Belin, Toulouse 31400, France
*
Author to whom correspondence should be addressed.
Academic Editors: Guoqing Zhou and Prasad S. Thenkabail
Received: 24 March 2017 / Revised: 28 April 2017 / Accepted: 3 May 2017 / Published: 10 May 2017
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Abstract

The secondary wave field associated with undular tidal bores (known as whelps) has been barely studied in field conditions: the wave field can be strongly non-hydrostatic, and the turbidity is generally high. In situ measurements based on pressure or acoustic signals can therefore be limited or inadequate. The intermittent nature of this process in the field and the complications encountered in the downscaling to laboratory conditions also render its study difficult. Here, we present a new methodology based on LiDAR technology to provide high spatial and temporal resolution measurements of the free surface of an undular tidal bore. A wave-by-wave analysis is performed on the whelps, and comparisons between LiDAR, acoustic and pressure-derived measurements are used to quantify the non-hydrostatic nature of this phenomenon. A correction based on linear wave theory applied on individual wave properties improves the results from the pressure transducer (Root mean square error, R M S E of 0 . 19 m against 0 . 38 m); however, more robust data is obtained from an upwards-looking acoustic sensor despite high turbidity during the passage of the whelps ( R M S E of 0 . 05 m). Finally, the LiDAR scanner provides the unique possibility to study the wave geometry: the distribution of measured wave height, period, celerity, steepness and wavelength are presented. It is found that the highest wave from the whelps can be steeper than the bore front, explaining why breaking events are sometimes observed in the secondary wave field of undular tidal bores. View Full-Text
Keywords: undular bore; non-hydrostatic processes; LiDAR scanner; wave-by-wave analysis undular bore; non-hydrostatic processes; LiDAR scanner; wave-by-wave analysis
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Martins, K.; Bonneton, P.; Frappart, F.; Detandt, G.; Bonneton, N.; Blenkinsopp, C.E. High Frequency Field Measurements of an Undular Bore Using a 2D LiDAR Scanner. Remote Sens. 2017, 9, 462.

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