Multibeam, multifrequency sonar method and apparatus

Abstract

The present invention relates to a sonar method and apparatus of tracking objects underwater. Specifically, the method and apparatus can be used to acoustically track a multitude of objects in a hemi-spherical volume 360° azimuth and 180° elevation relative to the location of the apparatus. The method and apparatus of the present invention provide four-dimensional, real-time tracking of underwater objects.

1 . A sonar head arrangement for detecting objects, comprising:
 four arrays of sonar elements in an azimuthal plane arranged so that each said array is angularly displaced from the next adjacent array by substantially 90°, said sonar elements projecting sonar beams outwardly and downwardly in a direction orthogonal to the said azimuthal plane such that the beams projected from each array intersect with beams projected from each angularly adjacent array and wherein said sonar elements are adapted to detect said projected beams when reflected from the object.   
   
   
       2 . The sonar head arrangement of  claim 1 , wherein:
 each array comprises a plurality of sets of sonar elements, each set comprising at least two sonar elements, each sonar element projecting beams within a predetermined angular range, wherein the totality of all the predetermined angular ranges of all of the beams in the array are substantially equal to 180°.   
   
   
       3 . The sonar head arrangement of  claim 2 , further comprising:
 at least one sonar element at the center of said array projecting sonar beams downwardly in a direction orthogonal to the said azimuthal plane.   
   
   
       4 . The sonar head arrangement of  claim 3 , wherein:
 each array has at least four sets of sonar elements.   
   
   
       5 . The sonar head arrangement of  claim 4 , wherein:
 each sonar element in each set oppositely projects beams to either side of said array within an angular range from horizontal, namely: the first set substantially within the angular range of 0° to 12°, the second set substantially within the range of 12° to 25°, the third set substantially within the in the angular range of 25° to 43° and the fourth set substantially within the angular range of 43° to 70°, and wherein said at least one center sonar element projects a conical beam having a width of about 40°.   
   
   
       6 . The sonar head arrangement of  claim 5  having two center sonar elements wherein; 
     the first center sonar element projects a conical beam having a width of substantially 40° and a second centre sonar element projects a conical beam having a width of substantially 10°. 
   
   
       7 . A sonar head arrangement according to  claim 1 ,  claim 2  or  claim 3 , wherein:
 said sonar elements detect sonar waves of a particular frequency which is different from that detectable by the other said sonar elements.   
   
   
       8 . A method for locating an object in a body of water, comprising the steps of:
 providing a sonar head of  claim 1 ;   determining the depth of the body of water and adjusting the rate of transmission of a transducer of each sonar element in the sonar head arrangement based on the depth of the body of water;   transmitting sonar beams at each sonar element at a particular frequency;   receiving sonar beams reflected by the object in at least one sonar element of at least one pair of angularly adjacent arrays; and   determining the position of the object based upon distance and downward angle.