Jenna Hare, doctorante au département d'Océanographie de l'Université Dalhousie, présentera une conférence le 19 février 2019 à 13h30, à la salle 2301 du Centre Eau Terre Environnement de l'INRS.
Sa conférence s'intitule Underwater Interaction of Sound and Sediment : Measuring Sediment Transport using MHz Frequencies.
Bienvenue à tous !
Résumé : Simultaneous measurements of nearbed flow and sediment transport represent a major challenge in aqueous environments. During the past 20 years, significant advances have been made using acoustic remote sensing for the study of sediment dynamics in the ocean. These developments have included broadband MHz frequency acoustic systems capable of simultaneous measurements of backscatter amplitude and phase at mm-scale range resolution. The overall research objective is to extend acoustic measurements to allow an acoustic estimation of bedload parameters. As an analogue for bedload transport, sub-aqueous granular flow on a sloping bed is investigated using a chute fully immersed in water. The thickness and velocity of the moving layer are measured with a wide bandwidth coherent Doppler profiler. High (MHz) frequencies are needed to resolve the moving layer, but sound attenuation at these frequencies may limit penetration through the layer and thus, prevent the measurement. In order to explore the range of frequencies which might be suitable, transmission loss, reflection loss and sound speed measurements within water-saturated granular material were made using a pair of broadband, calibrated transducers over 1 to 2 MHz. Natural sand and glass beads with median grain sizes ranging from 0.22 mm to 0.50 mm were used. The results are compared to Schwartz and Plona’s (1984) multiple scattering theory as well as to previous experimental results reported in the literature.