Synthetic aperture side-looking sonar apparatus

Synthetic aperture side looking sonar apparatus comprising:

• a) an elongated side looking sonar receiver transducer having a forward end and an aft end and being of a length L;
• b) said receiver transducer being made up of a plurality of elements, arranged end to end and each providing a respective output signal in response to reflected acoustic energy from a target area sonified by repetitive acoustic transmissions during travel over said target area;
• c) first and second transmitter transducers each of a length <L, respectively positioned proximate said forward and aft ends of said receiver transducer and separated by a distance t;
• d) transmitter means operable to provide a first transmitter signal of frequency F1 and a second transmitter signal of frequency F2 and to simultaneously apply said F1 signal to said first transmitter transducer and said F2 signal to said second transmitter transducer for propagation of acoustic energy, when said apparatus is at a position along said course of travel;
• e) said transmitter means being additionally operable, when said apparatus is at a next subsequent position to reverse the application of said F1 and F2 signals so as to apply said F1 signal to said second transmitter transducer and said F2 signal to said first transmitter transducer, and thereafter at each next subsequent position to reverse said application of said F1 and F2 signals from that of the previous position;
• f) receiver means operable to receive reflected acoustic energy resulting from said acoustic transmissions and to store the output signals of said elements from one transmission and combine them with the output signals resulting from a next transmission to form a plurality of receiver beams, characterized by respective beam signals;
• and
• g) means for utilizing said beam signals.