A multibeam echosounder is a type of sonar that is used to map the seabed. This is a device typically used by hydrographic surveyors to determine the depth of water and the nature of the seabed. Like other sonar systems, multibeam systems emit sound waves in a fan shape beneath a ship's hull. The time it takes for sound waves to bounce off the seabed and return to a receiver is used to determine water depth. Unlike other sonars, multibeam systems use beamforming algorithms to extract the directional information from the returning soundwaves, producing a swath of depth readings from a single ping.
Most modern echo sounder systems work by transmitting a broad acoustic fan shaped pulse from a specially designed transducer across the full swath acrosstrack with a narrow alongtrack then forming multiple receive beams (beamforming) that are much narrower in the acrosstrack (around 1 degree depending on the system). From this narrow beam, a two way travel time of the acoustic pulse is then established utilizing a bottom detection algorithm. If the speed of sound in water is known for the full water column profile, the depth and position of the return signal can be determined from the receive angle and the two-way travel time.
In order to determine the transmit and receive angle of each beam, a multibeam echosounder requires accurate measurement of the motion of the sonar relative to a cartesian coordinate system. The measured values are typically heave, pitch, roll, yaw, and heading. To compensate for signal loss due to spreading and absorption a time-varied gain circuit is designed into the receiver. For deep water systems, a steerable transmit beam is required to compensate for pitch through the process of beamforming. To change the directionality of the array when transmitting, a beamformer controls the phase and relative amplitude of the signal at each transmitter, in order to create a pattern of constructive and destructive interference in the wavefront.