Discrete volumetric acoustic and resistivity method and apparatus for sub-seabed surveying

A sub-bottom geophysical imaging apparatus includes a carriage assembly having at least one acoustic transmitter, and at least one acoustic receiver proximate the transmitter. A position determining transponder is mounted on the carriage. A plurality of position transponders is disposed at spaced apart positions to communicate with the transponder mounted on the carriage. A pair of tracks is provided for moving the carriage to selected positions above the bottom. Electrodes are provided for a resistivity sensor and a shear acoustic transmitter and receiver disposed in at least one of the pair of tracks. A signal processing unit is configured to coherently stack and beam steer signals detected by the line array, the electrodes and the shear transmitter and receiver. The signal processing unit is configured to record signals detected by the line array of acoustic receivers, the electrodes and the shear acoustic transmitter and receiver.