A vessel towed platform for deepwater high resolution benthic imaging

Towed underwater imaging systems are increasingly used for a wide variety of science applications in the deep ocean. These systems augment data collected by physical sampling such as dredging and trawling, but also provide an important sampling alternative where extractive methods are unnecessary or unsuitable - such as in sensitive habitats or for repeated sampling in marine reserves. Specific applications of image-based sampling are to ground-truth habitat maps at scales of kilometers and quantitatively map benthic biodiversity, i.e. along transects with robust statistical properties (straight with constant speed and height off bottom). The opportunities for scientists to study the deep ocean was boosted in 2015 with the arrival of Australia's new custom built research vessel, RV Investigator. Deep water imaging was identified as a critical capability for the new vessel, and the past experience of engineers and scientists at the Commonwealth Scientific and Industrial Research Organization (CSIRO) have been combined to design and develop a system suited to a variety of user groups and applications - specifically to provide a system capable of repeated, rapid deployments to the seabed to depths of 4000 m. The study of the deep ocean is particularly challenging with vessel-towed gear because of the engineering considerations in design of depth rated components and remoteness of the platform from the vessel (typically kilometers). The system is towed by an electro-mechanical fiber optic cable. This allows the imaging system and sensor suite to be monitored and controlled in real time from the ship's science operations room during all phases of a deployment. The platform is equipped with several imaging systems, with options for future expansion. A high resolution DSLR camera paired with a high definition video camera provide the benthic science data. These two cameras are focused on the bottom to give an oblique perspective, with illumination provided by four LED lights. The settings of both the DSLR camera and lighting system can be adjusted in real time. A pair of lasers with known separation is used to scale the field of view of both the video and the digital stills system. To aid in navigation and obstacle avoidance, a forward looking camera is used. In addition to imaging, the system is equipped with a CTD and altimeter, and has the capability to accommodate additional sensors. A USBL beacon permits accurate targeting of particular seabed features.