A method for imaging formations below the bottom of a body of water includes imparting acoustic energy into the formations along a predetermined length swath at a selected geodetic position. Acoustic energy reflected from the formations is detected along a line parallel to the length of the swath. The selected geodetic position is moved a selected distance transverse to the length of the swath. The imparting acoustic energy, detecting acoustic energy and moving the geodetic position are repeated until a selected distance transverse to the length of the swath is traversed. The detected acoustic energy from all the selected geodetic positions is coherently stacked. The detected acoustic energy is beam steered 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.