 Gas plumes now commonly identified in midwater multibeam data are termed flares.A multibeam echosounder is a device typically used by hydrographic surveyors to determine the depth of water and the nature of the seabed.Most modern 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).