Multibeam, multifrequency sonar method and apparatus

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.