Deepwater Technology
Faced with alarming declines in the health of marine ecosystems, scientists urgently need the ability to monitor marine biota - to 'see' beneath the ocean’s surface. Beyond 20 meters, this requires expensive technology and operational expertise. Scuba divers simply can’t work for very long at 20 meters (only about 60 minutes), and beyond 60 meters, scuba surveys are generally not feasible.
The technologies currently available for visual marine observation are remotely operated vehicles, manned submersibles, autonomous underwater vehicles and tow sleds.
MARE provides ROV surveys to depths of 650 meters and manned submersible surveys to 300 meters.
Remotely Operated Vehicles (ROVs)
ROVs are highly maneuverable underwater robots operated in real time by a person aboard a surface vessel. They are linked to the ship by an umbilical cable that transmits visual and other data between the operator and the vehicle.
ROVs can operate continuously, 24 hours a day, and can easily fly close to the seafloor, even over rugged terrain. They also have the ability to carry manipulators, sensors, and samplers.
Manned Submersibles
Manned submersibles are extremely expensive to operate but allow direct species and habitat observation with or without the use of cameras. A few can go as deep as 6,000 meters.
There are two main classes of manned submersibles. Conventional submersibles, such as the Delta or Alvin, use ballast systems for buoyancy control. They are very stable, slow and can hover. Winged submersibles, such as Deep Flight, are highly maneuverable and can fly at rapid speeds over rugged terrain. With no ballast system, they are positively buoyant and rely on forward movement to remain submerged.
Photos: Woods Hole Oceanographic Institution (left), Hawkes Ocean Technologies (right)
Autonomous Underwater Vehicles (AUVs)
AUVs fly pre-programmed paths to collect video and still images. They are dropped off and then retrieved up to 48 hours later, which reduces staff costs and is a benefit for launch in rough seas or constricted areas (i.e. ice). AUV communication with the surface is limited; they usually calculate their position based on their movements, and accuracy declines over the duration of the dive. If lost, all the data for that dive is lost, too.
Photo: NOAA
Tow Sleds
Tow sleds, like ROVs, are connected to the surface by an umbilical cable. Without thrust, however, sleds are simply towed behind a vessel and have limited ability to follow the seafloor over rocky, rapidly changing terrain. Most can be maneuvered only by using a winch to shorten or lengthen the tether or by varying boat speed.The sled flies lower at slower speeds and higher at faster speeds.