A seabed region (18) that lies under a seabed surface area of over one square meter, is analyzed by comparing a core sample taken near the middle of the region and/or data from a geotechnical insitu cone penetrometer installed at the middle of the region, to an acoustic analysis of the region. Locations of the acoustic analysis are precisely correlated to the location of the core test sample or cone test by mounting an acoustic imaging apparatus (16) that holds acoustic transducers (44, 46), on a carriage (26) that is positioned on the core drill (12) or cone penetrometer barrel staff. The carriage of the acoustic imager apparatus is clamped to the core drill when the core drill is not rotating. An arm (30 and/or 32) is supported on the carriage through a frame (28), with at least one acoustic generator (44) and one acoustic echo detector (46) mounted on the arm. The arm can be rotated to positions lying about the drill axis (14) to accurately scan a wide area.