A prototype underwater camera system has been developed by U.S. Geological Survey (USGS) scientists to take repetitive microscopic images of the seabed from a tripod on the sea floor.
The images, which record changes in seabed sediment over time, are used in studies of how changes in sediment grain size influence rates of sediment movement. Understanding sediment movement is important to applied researchabout sea-floor habitats, for example, or about pollutants, which move like sedimentand to basic research about the sea floor.
The camera system was developed as part of the multinational Strataform Project, a program funded by the Office of Naval Research that seeks to understand geologic processes on the continental shelf and slope that form sedimentary strata over a continuum of scales. Dubbed the "Poking Eyeball," the system performed well in its first sea trial, begun last fall during a cruise to investigate sediment transport in the Adriatic Sea.
The new camera system consists of five major components: power pack, water pump, digital camera, electronic controller, and miniwinch, all designed to be mounted on a tripod that sits on the sea floor. So as not to interfere with the current flow or with other data-gathering instruments on the tripod, the camera is winched up and down 1 m from a protective housing every 12 hours. The electronic controller, a modified 12V lawn-irrigation timer, determines the up-and-down movements and the bottom-pause time for the winch motor.
The winch motor is connected to a spool with a line attached to the camera housing to raise and lower it to the seabed. The camera housing, about 10 lb negatively buoyant, contacts the seabed and remains there for about 4 minutes. During this time, the camera's internal timer triggers the camera and a synchronized ring-light flash and the camera takes one photograph. The electronic controller then raises the camera back into its protective polyvinyl chloride (PVC) housing. A mercury switch located at the top of the PVC housing triggers the electronic controller to stop the winch once the camera housing has reached its topmost position.
The electronic controller also determines the start and stop times of a water pump, which circulates pressurized seawater through a series of tubes to the front window of the camera housing, keeping it sediment free. The water pump operates four times each day for 1 minute, just before and after the camera's twice-daily contact with the seabed.
A Canon D60 digital camera with a 6.3-megapixel CMOS (complementary metal-oxide semiconductor) sensor is the heart of the imaging system. The lens, which is capable of 1X to 5X magnification and surrounded by a ring-light flash, produces well-focused images, resolving grain sizes in the silt range, shell fragments, and feces trails and pellets.
After last fall's deployment in the Adriatic Sea, the system successfully operated for 8 days until strobe power and winch malfunction shut the system down. Although 8 days was not the duration of operation we had hoped for (we had hoped the camera would operate for the full 101 days that the tripod was on the sea floor), the design concept was proven to work. Some repair work and system reconfiguration enabled us to redeploy the Poking Eyeball on February 19. We will assess the reconfigured system's performance after it is recovered in late May.
This system and its concept build on a previous system (a.k.a. the "Flying Eyeball"; see article in June 2001 Sound Waves ) that uses low-resolution video technology to capture underwater black-and-white microscopic images of sand on a seabed or riverbed. The added features of the new system are:
Special thanks to the staff of the USGS Marine Facility (Marfac) in Redwood City, CA, for their engineering, mechanical, and logistical expertise in helping get this baby out the door. Considering the short, 2-month timetable to get the entire package together, and that last fall's deployment in the Adriatic Sea was its first saltwater deployment, we think all involved in the new system's production can be proud of its initial results.
in this issue: Adriatic Sea Instrument Redeployment
Prototype Underwater Camera System