Alex E. Hay
Dept. of Phys., Memorial Univ., St. John's, NF A1B 3X7, Canada
Sediment transport in the oceanic bottom boundary layer involves threefold coupling among: (1) the motion of sediment grains; (2) the response of the bed; and (3) the fluid forcing. The appeal of acoustic remote sensing methods is that in principle all three components of the problem can be addressed with minimal disturbance to the system. This paper reviews the progress that has been made to date toward developing acoustic instrumentation systems for sediment transport measurements in the nearshore zone, where sand is the principal component of the bottom sediments. Instrument developments are discussed in relation to several types of measurement requiring multiple acoustic beams: (1) range-gated multifrequency backscatter to obtain profiles of suspended sediment concentration and size, and the associated inverse problem; (2) bedform imaging with fan-beam sonars; (3) suspended sediment fluctuations under waves. The results provide revealing insights into the sediment transport process, and thus demonstrate the effectiveness of the multibeam approach. The results also raise a number of fundamental questions. Some of these questions can be addressed with the instrumentation currently at hand. Others will require a new generation of instruments.