An evaluation of the use of a multibeam echo-sounder for observations of suspended sediment

The theory relating the acoustic backscatter from suspended sediments to the mass concentration of particles has been developed over several decades and is now routinely applied to provide measurements for commercial and scientific applications. Single-beam instruments, such as acoustic Doppler current profilers (ADCP), permit acquisition of backscatter along one-dimensional spatial profiles. However, commercially available multibeam echo-sounders (MBES), designed principally for bathymetric surveying, now offer water column backscatter data-logging across their two-dimensional interrogation swaths, enabling suspended sediment to be instantaneously imaged across much larger volumes. This paper addresses issues relating to the processing of suspended sediment backscatter recorded with an MBES system, drawing on the theory developed for single-beam instruments. A processing methodology is developed and the performance limits estimated from an analysis of the data acquired in the near-field of a Teledyne-RESON MBES in a controlled test facility. Results derived from the application of the methodology to field-data collected with an MBES and an ADCP in the Missouri River, USA, are presented that demonstrate the potential gains in spatial and temporal resolution and near-bed imaging than can be achieved by the use of an MBES system.