Human activity in the marine environment is an important component of the total oceanic acoustic
background. Sound is used both as a tool for probing the ocean and as a byproduct of other activities.
Anthropogenic noise sources vary in space and time, but may be grouped into general categories: (a) large
commercial ships, (b) airguns and other seismic exploration devices, (c) military sonars, (d) ship-mounted
sonars, (e) pingers, (f) acoustic harassment devices (AHDs), (g) polar ice-breakers, (h) offshore drilling
implements, (i) research sound sources, and (j) small ships.