High-energy events, boulder deposits and the use of very high resolution remote sensing in coral reef environments

Abstract

Collin, A., Etienne, S. and Planes, S., 2013. High-energy events, coastal boulder deposits and the use of very high resolution remote sensing.In recent years, coastal boulders have become a trendy proxy in studying high-energy marine inundation events. From their morphology and spatial distribution, authors are able to characterize a singular event in terms of intensity (wave height, flow velocity). Recent post-catastroph studies (e.g. Indian Ocean 2004 and Japan 2011 tsunamis) have demonstrated also the interest of boulder deposits in reconstructing the event kinematics through a multi-proxy approach. But as boulder studies require a statistically robust dataset they are field-time consuming and sometimes fieldwork takes place in remote areas with low facilities. The use of very high resolution remote sensing could overcome some of these limits. In this paper, we evaluate the possibility to identify meter-size coral boulder thrown on a reef flat during the hit of a tropical cyclone. Image analysis allows for the discrimination of major geographical object encountered on coralline islands: submerged coral boulder, emerged coral boulder, perched reef, sand beach. Within emerged boulder population, specific bands available with WorldView-2 images (i.e. red and NIR2 band) allow the spectral discrimination and mapping of fresh and weathered elements.