Hard and soft bottom
The basis of NGU's "Hard and Soft Bottom" maps is information collected from multibeam echosounders. This instrument is used for detailed mapping of water depths (bathymetry), but researchers can also interpret the morphology and composition of the seabed through the strength of the signals reflected back. When the bottom reflectivity data (back scatter) are processed, it is possible to acquire detailed information on variations in the types of seabed.
Bottom reflectivity depends upon several factors. A hard or coarse-grained, cobble type of seabed usually gives a strong signal; whereas, weaker signals are reflected by fine-grained sediments which tend to absorb signals. Other factors influencing the bottom reflectivity are evenness of the surface, and how well the sediments are sorted.