This is a continuous sub-bottom profiling system designed to give high resolution whilst retaining good penetration. By mounting the output transducer in the bottom of a fibreglass dinghy, towed well astern of the survey ship, the shortest possible output pulse has been achieved, and by using a line hydrophone towed between the ship and dinghy a very low background noise level has been obtained.Using this system, surveys are carried out at 7½ knots with a resolution of 6 ft and a penetration of up to 1000 ft.