The basis of NGU's "Acoustic backscatter" 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. When the seabed reflectivity data (backscatter) are processed, it is possible to acquire detailed information on variations in the types of seabed.
Seabed 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 seabed reflectivity are evenness of the surface, and how well the sediment sorting.