K. Martins, P. Bonneton, D. Lannes, C. Blenkinsopp


In recent years, remote sensing technology (e.g., lidar or stereo-video imagery) has seen tremendous developments and now allow 
the collection of accurate and direct measurements of the sea-surface elevation in the nearshore region. In this presentation, 
we will focus on recent experiments that employed both traditional pressure sensors and 2D lidar scanners to monitor the time-varying 
free surface elevation associated with breaking and broken waves in the surf zone. In contrast to the traditional ‘single-point’ 
in-situ instrumentation, lidars directly capture the wave profile and thus provide unprecedented levels of detail on wave transformation 
processes around breaking in the field. Non-linear and non-hydrostatic effects are found important everywhere in the surf zone: 
from the outer surf region, where waves initiate breaking, to the inner surf region where they propagate as bores. 
Yet, traditional methods for the reconstruction of the free surface from pressure measurements in the surf zone either 
neglect these non-hydrostatic effects or approximate them with linear wave theory. At the wave-by-wave scale, this results in 
the underestimation of the steepness and wave crest maximal elevations as seen by the pressure sensors. 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. 
The performance of this irrotational method supports the hypothesis that the flow under broken waves is dominated by irrotational motions.