Détection de courants marins côtiers à partir de séquences vidéo
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Date
2014
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Abstract
Les courants marins à proximité d’une côte contrôlent le transport de sédiment et son évolution. Or leur estimation par des instruments sur site est difficile et coûteuse. Les systèmes de télédétection reposant sur des observations constituent une alternative prometteuse lorsque la mousse dérivante laissée après le passage de vagues déferlantes est visible. Pourtant, seules quelques méthodes ont été proposées à ce jour dans la littérature.Dans cet article, nous décrivons deux nouvelles méthodes : l’une basée sur les images vidéos considérées dans leur globalité et l’autre basée sur des timestacks le long de la côte. La première approche est une extension de la méthode Particle Image Velocimetry (PIV). La seconde approche produit une estimation de la composante parallèle à la côte des courants de surface en utilisant la transformée de Radon sur des séries temporelles de données en une dimension. Cette dernière nécessite moins de données.Les vidéos utilisées dans cet article proviennent d’une campagne menée sur la zone de l’embouchure de Mataquito dans la région de Maule au Chili. Elles font partie d’une étude sur l’évolution côtière de la zone de Mataquito après le tsunami chilien de 2010. Une comparaison a été également réalisée avec les mesures d’un courantomètre prises lors de la campagne du Truc Vert de 2008 en Aquitaine, France. Elle a eu lieu lors d’une tempête qui a provoqué l’évolution d’une barre sableuse.
In nearshore applications, the estimation of currents is of primary importance since it controls the sediment transport and coastal evolution. Direct estimation of currents using in-situ instruments is difficult and costly. Low cost remote sensing systems based on video observations constitute a promising alternative when the drifting sea foam left after the passage of breaking waves is visible. Only few methods have been proposed in the literature to take advantage of this.In this paper we describe two new methods: one based on the full video frames and one based on longshore timestacks that necessitates less data. The first approach is an extension of Particle Image Velocimetry method. The second approach uses the Radon transform applied on the time series derived from timestacks to produce an estimate of the longshore component of nearshore surface currents detected from the foam signature in video images.The videos used in this article come from a field campaign conducted in the Mataquito rivermouth area in the Maule region (Chile). They are part of a study on the post-tsunami coastal recovery of the Mataquito area after 2010 Chilean Tsunami. Field tests comparison was also made against in situ current meter from the 2008 Truc Vert experiment in Aquitaine (France). It took place during a tempest which has provoked a sandbar evolution.
In nearshore applications, the estimation of currents is of primary importance since it controls the sediment transport and coastal evolution. Direct estimation of currents using in-situ instruments is difficult and costly. Low cost remote sensing systems based on video observations constitute a promising alternative when the drifting sea foam left after the passage of breaking waves is visible. Only few methods have been proposed in the literature to take advantage of this.In this paper we describe two new methods: one based on the full video frames and one based on longshore timestacks that necessitates less data. The first approach is an extension of Particle Image Velocimetry method. The second approach uses the Radon transform applied on the time series derived from timestacks to produce an estimate of the longshore component of nearshore surface currents detected from the foam signature in video images.The videos used in this article come from a field campaign conducted in the Mataquito rivermouth area in the Maule region (Chile). They are part of a study on the post-tsunami coastal recovery of the Mataquito area after 2010 Chilean Tsunami. Field tests comparison was also made against in situ current meter from the 2008 Truc Vert experiment in Aquitaine (France). It took place during a tempest which has provoked a sandbar evolution.