BLOG 5: Mapping

By Chris Meagher

A critical goal of this voyage is the underwater seabed mapping which occurs continuously whenever the ship is moving. The mapping systems onboard the RV Investigator send sound waves down to the seabed and measure the return time of the signal to determine the distance. This is similar to the echolocation systems used by bats. Computer software then interprets this data to develop a detailed map of the shape of the seabed topography or bathymetry. Sonar technology is used as sound waves have been found to travel through water much better than radio waves or other types of radiation.

The RV Investigator is equipped with two main bathymetry mapping systems, used in different water depths. The shallow water echo sounder EM710 emits sound waves at 100 KHz and is used to map features to a depth of 1000m.  The full depth echo sounder EM122 can map features from 100m to seabeds in the deepest part of the ocean using 12 KHz sound waves. Both of these systems use a multibeam echo sounder which simultaneously sends 512 sound signals (or beams) all at slightly different angles.  Waters on this voyage are often 5 km deep and in these areas the multibeam is mapping a strip or swath of seabed 16 km wide.

The sub bottom profile sends down a single beam of very low frequency 12 KHz sound waves which can actually penetrate the seabed and penetrate to a depth of 100 m and provides details of the different sediment layers which lie below the seabed.

Many of the seamounts on the Balleny chain have not been mapped before so the ship must make a number of passes over some of the seamounts. Scientists on board the ship use the mapping data to determine the size and shape of the seamounts so they can then identify the best potential locations to dredge for rocks. Geologists will also use the mapping data back on shore to identify features and thereby help them to understand how the seamounts formed.