Discrete volumetric sonar method and apparatus for sub-seabed surveying

A method for imaging formations below the bottom of a body of water, comprising:

• imparting acoustic energy into the formations along a predetermined length swath at a selected geodetic position using at least one acoustic transmitter mounted to a carriage assembly;
• detecting acoustic energy reflected from the formations along a line parallel to the length of the swath at the selected geodetic position using a line array of acoustic receivers mounted to the carriage assembly;
• detecting acoustic energy reflected from the formations using at least two substantially orthogonal line arrays of acoustic receivers deployed on the bottom of the body of water;
• moving the selected geodetic position a selected distance transverse to the length of the swath;
• repeating the imparting acoustic energy, detecting acoustic energy and moving the selected geodetic position until a selected distance transverse to the length of the swath is traversed;
• coherently stacking the detected acoustic energy from all the selected geodetic positions;
• and
• beam steering the detected acoustic energy to each of a plurality of depths and positions along the length of the swath to generate an image for each such depth and position.