the amount of sound radiated by a sound source. It is defined as the intensity of the radiated sound at a distance of 1 meter from the source, where intensity is the amount of sound power transmitted through a unit area in a specified direction. Source level is given as a relative intensity in units named decibels (dB). In underwater sound, decibels are referenced to a pressure of 1 microPascal (µPa). Therefore, source level is reported in units of dB re 1 µPa @ 1 m.