The multibeam echosounder

What is a multibeam echosounder ?

The system, mounted on the hull of a ship, measures the water depth from the surface at several points simultaneously from port to starboard.  The swath can reach up to 20 km wide and 5 000 m deep.

How does it work?

To measure water depth, the system emits acoustic waves in a fan shape beneath the transceiver of the multibeam echosounder. The length of time it takes for the sound waves to reflect off the seabed and return to the receiver is used to calculate the water depth.

What does it study?

This tool is primarily used to obtain the bathymetry (= depth) of the oceans. Depth is the basic information required for studying the morphology of the ocean floor, and therefore all geological structures: oceanic ridges, volcanoes, faults, canyons, landslides, Knowledge of the morphology of the seabed makes it possible to draw up navigational maps, to decide on the development of a coastline, or to determine the ideal route of an underwater cable.

But this tool also measures the intensity of reflected echo, which is called reflectivity. The intensity of the echo is directly related to the nature of the seafloor:

• looser sediments (mud, mud), provide lower reflectivity.
• Conversely, a harder and more consolidated seafloor (pebbles, rock), provides greater reflectivity.

It is therefore possible to determine both the nature and shape of the seabed simultaneously which can be useful for example to draw up a habitat map: we now know that Norway lobster live preferentially on flat and muddy areas.