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Underwater Robots Clean Up Marine Debris on the Seafloor

By Rachael Z. Miller

An image from the Starfish side scan sonar of a shipwreck with an active trap line along the side and some potential derelict traps (singles) along the bottom of the image. (Photo credit: Rozalia Project for a Clean Ocean)

Marine debris is a problem found everywhere from coasts to rivers to lakes and into the center of the gyres. This man-made debris can take decades or centuries to degrade, and even then, material such as plastic may never fully degrade in the marine environment, only break up into smaller and smaller pieces. This persistent material entangles and strangles marine life, transports alien and invasive species among ecosystems, pollutes beaches, fouls propellers, and has now been found, through ingestion by creatures low on the food chain, to transfer persistent organic pollutants into the human food chain through biomagnification.

The majority of marine debris comes from land rather than ships. While much of it is due to carelessness and runoff, extreme weather and geologic events, such as the tsunami off the coast of Japan and Hurricane Sandy along the Northeast U.S., have made significant contributions to the amount of debris drifting with ocean currents and sitting on the seafloor. Debris poses threats to shipping and the safety of people onshore.

Rozalia Project for a Clean Ocean's mission is to use technology to find and remove marine trash and debris from the surface to the seafloor without having to resort to potentially damaging methods such as grappling (dragging hooks along the seafloor to grab debris). The project also employs towed and hand-held surface nets, as well as shoreline walks.

Cleanup Equipment
In terms of the equipment, Rozalia Project requires portability and a small footprint for the control station, as well as the ability to operate and see in a variety of marine environments, carry out close-in work and wide area searches, identify and mark locations, and pick up a variety of objects.

The project uses a VideoRay LLC (Phoenixville, Pennsylvania) Pro 4 micro-ROV, a BlueView Technologies Inc. (Seattle, Washington) 900-45 multibeam sonar, a KCF Technologies (State College, Pennsylvania) Smart Tether positioning system, a Tritech International Ltd. (Aberdeen, Scotland) StarFish 450F side scan sonar and a LYYN AB (Lund, Sweden) image enhancement system.

Collecting Debris From Boston Harbor
In July 2011, Rozalia Project was operating from the Charlestown Navy Yard in Boston Harbor, running cleanup and education programs. The cleanup focused on an area off the docks of Courageous Sailing Center in 30 to 40 feet of water, with an average visibility of 10 to 18 inches. Though this was a target-rich environment with a seafloor covered in debris, it was still important to stay organized, keep track of areas cleaned and keep the ROV away from a section of dock pilings that posed a fouling hazard for the tether.

The critical piece of equipment for this operation was the BlueView multibeam sonar, mounted on the VideoRay Pro 3 GTO (Greater Thrust Option) ROV system. The BlueView sonar revealed tires, large pieces of discarded metal, piles of beer cans and plastic cups, as well as crabs walking across the bottom. The ROV pilot was repeatedly able to fly the VideoRay directly to specific targets, such as a single can, acquired from over 30 feet away. Once the VideoRay was within 1 to 2 feet of the target, the LYYN image enhancement system allowed enough visibility to use the manipulator to retrieve the object, get it to the surface and return for more.

Cans, cups, utensils and food wrappers are among the most frequently found items of debris recovered from the bottom of waterways, floating on the surface and along the shoreline. In this case, a large number of cans and plastic cups were found clustered together in different sections of this part of Boston Harbor, and underwater cleanup efforts were focused on those objects. The cleanup progress was sped along with the BlueView sonar's ability to reveal piles of cans and cups with enough clarity for the Rozalia team to count them while still 10 to 30 feet away. To continue this article please click here.

Rachael Miller is the co-founder and executive director of Rozalia Project for a Clean Ocean. She has a background in marine studies and underwater archaeology, which she studied at Brown University. She is a trainer for VideoRay LLC and founder of Lake Champlain Shipwrecks, running the first commercial, ROV-supported shipwreck tours in the U.S.

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