Multiple beam generation with a digital computer for echosounding at low and high frequencies

The fact that the velocity of sound in (sea)water does not vary much enables us to determine through ray theory the direction from which underwater sound is received. In the same manner the direction can be chosen in which underwater sound is emitted. These principles are applied in echosounders for hydrographic use (Glenn, 1970, Burke and Robson, 1975) sidelooking sonars (Belderson, et al., 1972), sectorscanning sonar (Tucker, 1960, Ballard and van Andel, 1977, Wolff, 1976) and imaging echosounders (Metherel et al., 1969). The class of hydrographic echosounders can be divided into narrowbeam systems and multi-beam systems. The former use an antenna, i.e. an array of transducers, to generate a single beam with a small beamwidth, the latter generate several beams with different azimuths. Up to now the most sophisticated deep-sea multibeam echosounders (Sonarray Subsystem, Glenn, 1970, and Seabeam, Renard et Allenou, 1979) generate simultaneously beams with different azimuths, utilizing electronic circuits. These beams lie in a plane perpendicular to the ship's track. In that way information in three dimensions is gathered along one track, hence the name threee-dimensional echosounders.