Multibeam Echosounder

A multibeam echosounder is an active sonar system which relies on high-frequency (tens/hundreds of kHz) sound waves to map the seafloor. The three most commonly used outputs are bathymetry, seafloor backscatter, and water column data. Since its advent, this technology has exponentially increased our knowledge of the processes that sculpt the seafloor, revealing a large spectrum of geomorphic features associated with oceanographic, volcano-tectonic, sedimentary, and gravity-driven instability processes. Characterization of such features is used for the assessment of marine geohazards, while repeated bathymetric surveys are used to monitor rapid seafloor changes related to hazardous phenomena such as coastal erosion, landslides, active tectonics, and volcanism. Repeat bathymetric surveys have thus become a complementary tool to on-land remote sensing techniques. This chapter briefly illustrates (1) the architecture of multibeam systems, (2) the main techniques used for data processing, and (3) the uncertainties associated with bathymetric data and computation of depth changes and involved volumes. Finally, an example of repeated multibeam systems used to detect and monitor a complex eruption-driven sequence of submarine/subaerial instability processes at Stromboli volcano is presented.