The sub-bottom profiler emits acoustic pulses at low frequencies which penetrate the seafloor and are reflected due to density changes within the sediments. The sound waves return to the vessel at slightly different times and are displayed as a series of layers. This reveals past sedimentation patterns for the area.
There is good acoustic penetration through sand and soft sediments, up to 30 m, but this decreases through gravels, bedrock and gaseous sediments.
There are two general systems; a ‘pinger’ transmits a single frequency (~4 kHz) and the ‘chirp’ transmits a sweep of frequencies (e.g. 2-7 kHz) in a single pulse.