Side looking sonar beam forming utilizing the chirp Z-transform

Claim 1

Side looking sonar beam forming apparatus for travel over a target area for imaging the target area substantially laterally of the direction of travel of the apparatus, in response to acoustic returns from successive range increments as a result of acoustic transmissions sonifying said area, comprising: (A) a plurality of active elements arranged in an elongated line array with each being operable to provide an output signal in response to said acoustic returns; (B) means for providing a plurality of reference signals to simulate output signals of a plurality of fictitious elements added onto said array; (C) signal processing means responsive to all of said output signals for generating, for each said range increment, a plurality of beam signals indicative of acoustic returns received by a set of receiver beams radially extending from a position on said array; (D) means for indexing said position along said array and generating a different set of said receiver beams for each indexed position; and (E) means for selecting and displaying the same numbered beam signal of each said set formed as a result of said indexing.