Undersea geophysical exploration

Claim 1

A process for geophysical surveying of an undersea floor area to obtain information indicative of physical characteristics of material on the undersea floor comprising: (a) moving an undersea vehicle under water in a forward linear direction at a substantially constant altitude above the undersea floor; (b) transmitting bilaterally from said vehicle two underwater acoustic beams, one at a first frequency and the second at a second frequency, both frequencies being in the transmitting frequency range of 12 to 40 kHz and differing from each other by a difference frequency of at least 2 kHz and each with power sufficient to intersect, and produce perceivable echos from, the undersea floor; (c) said beams being directed bilaterally away from each other, one to the starboard and one to the port, with the acoustic axis of each beam in a plane perpendicular to the forward line of vehicle movement and slanted downward to intersect the undersea floorline at a grazing angle in the angular range of about 20° to 65°; (d) each of said two beams having a portion extending vertically down to the undersea floor and sideward from the vertical at least about one degree from each side of the downward vertical from the vehicle and forming a downwardly directed difference-frequency beam of at least about two degrees width impinging on the undersea floor; (e) perceiving underwater vibrations backscattered from where the starboard and port beams impinge on material of the undersea floor; (f) converting the perceived backscattered vibrations to electric signals indicative of the amplitude of the backscattered vibrations reaching the undersea vehicle; (g) displaying, storing or recording the amplitudes of the backscattered vibration signals; (h) perceiving acoustic vibration at the difference-frequency reflected upward from where the difference-frequency impinges on undersea floor material; (i) converting the perceived difference-frequency vibrations to electric signals indicative of the amplitude of the difference-frequency vibrations; and (j) displaying, storing or recording the amplitudes of the difference-frequency signals.