Developing new ground truthing techniques for seabed mapping

The purpose of the project was to develop a towed video sledge combined with low altitude sidescan system to obtain concurrent visual samples of the seafloor and high resolution acoustic images. It is intended that such a device would bridge the gap between standard sidescan survey and ground truth sampling. The specifications for the device were that the technology would be inexpensive, easy to use, deployable from small vessels and operate in depths of at least 30m.

A system has been designed meeting these specifications - this is known as a camera and low altitude sidescan (CLASS) device. It consisted of a sledge with sidescan trailing 1.3m above the sea floor from an attachment on the sledge towing cable. Bullet cameras were attached close to the sea floor for viewing in low visibility. A StarFish 450kHz chirp sidescan was connected to the surface using a local area network and the transducer unit was rendered slightly positively buoyant and directionally stable by attaching it to a fish with tail fins and net floats.

The design went through a series of tests and modifications. The final design of the sledge was small and light-weight and easily constructed from aluminium sheet and threaded steel bars.