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Deepseawaters
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Human Occupied Vehicle
Human
Occupied Submersible Hydrothermal vents were first discovered
in 1977 using the human occupied submersible Alvin. After
40 years of scientific research that led to the discovery
of new life forms and helped confirm the theory of plate tectonics,
the National Science Foundation is providing funding to replace
Alvin with a new, deeper-diving vehicle. The replacement vehicle
will be capable of reaching more than 99 percent of the seafloor
to depths of 6.5km (4 miles), 40% deeper than Alvin, which
currently dives to 4.5km (2.8 miles).
There
are six critical areas in which occupied submersibles far
exceed the capabilities of ROVs, engagement of the
operator, visibility from the vehicle,
maneuverability, unobtrusiveness,
reliability, and the capacity for
education, outreach and recruitment.
Engagement
Anyone who has dived
in a submersible knows what this means. When you are in the
submersible you are conscious of every sensation and you are
focused the whole time. To achieve this same level of engagement
of the human consciousness one would require nothing short
of complete virtual presence. We can't do that with ROVs yet.
Indeed the whole idea behind achieving virtual reality is
to simulate the human presence .
Visibility
The difference in
perception gained from looking out the porthole of a submersible
with the human eye in situ vs that from looking at video monitors
is the same as your view of this room right now vs what your
view of the room would be if you saw it with only one eye
while looking through a rectangular hole cut in the end of
a black box taped to your face.
Where ROVs visiting the same spot that had been visited previously
(and marked) by submersibles were unable to locate targets
because the field of view and the perception of the surroundings
are less complete. For example, at the same spot visited with
the Pisces V submersible a day before, an ROV driver never
found the target. A researcher spent a day looking for a given
type of small animal with an ROV and never found one, but
came back the next day with the Johnson Sea Link submersible
and immediately found many. Scientist revisited an Ocean Drilling
Program drill site target area marked previously using the
Shinkai 6500 submersible and could not recognize my marker
though staring directly at it for 5 minutes with a camera
mounted on the end of the drill pipe. And when ROV pilots
get a chance to dive with Alvin to areas where they have worked
many times, their customary reaction is surprise. "Patricia
Fryer, senior research scientist in Marine Geology
at the University of Hawaii. He never realized it was this
rugged down here."
For biological studies, observation of complex biosystems
is far better performed by human observers in situ, particularly
for perturbation experiments. Something critical may be happening
beyond the field of view of ROV cameras that an observer at
the site in a sub would catch with peripheral vision. The
same is true for some geological applications, the most effective
way to perform geological mapping is to have a skilled person
in situ looking at the structural relationships in 3-D and
tracing formation contacts. In some instances shimmering water
from gently effusive springs, which is critical for identifying
sampling sites, simply can't be seen with an ROV because of
the optical interference from video transmissions (screen
flutter).
Sampling is much easier with the parallax vision afforded
by the pilot looking out a view port than it is from a flat
video monitor in an ROV control room. The rate of sampling
is thus faster with a sub. Today's precision biological sampling
requirements demand the visibility afforded from a view port.
For many operations, including deploying large and awkward
seafloor observatory equipment, the power and lift capabilities
of a submersible are critical.
Maneuverability
The chief problem
ROV operators have in complex terrain is the difficulty of
avoiding fouling the tether. In active hot hydrothermal regions
you cannot land on up close to active vents with a tethered
vehicle and do detailed work for extended periods. The tether
would be in danger of destruction in the hot effluent. In
the recent efforts to examine and recover remains from the
Ehime Maru the first attempt to observe the ship failed because
the tether of the first ROV used was fouled in the ship's
rigging. Such problems do not present themselves for untethered
occupied submersibles. The Hawaii Undersea Research Laboratory
has been operating at Loihi Seamount, the active seafloor
volcano south of the Big Island, for years. After the 1996
eruptions at the summit, the topography of the site changed
dramatically with new pit craters and collapse features. The
Pisces V made numerous dives to the new site helping to establish
a seafloor observatory at the site and a 3-D map of the complex
new terrain. Both JAMSTEC and the Monterey Bay Aquarium Research
Institution had considered operations with their ROVs in the
new eruption site until they discussed the topography with
the Pisces V chief pilot. In the end, they both refused to
perform lowerings because of potential fouling hazards for
their tethers. Thus, whatever new scientific discoveries might
have been accomplished there with the ROVs will never be known.
Problems of managing the tether for an ROV become increasingly
difficult as current complexity, velocity, and as ocean depth
increase. JAMSTEC's Kaiko ROV, capable of operating at depths
in excess of 10,000 m (the world's deepest-capability ROV)
was designed to enable scientific work to be performed at
the Challenger Deep the deepest point in the world's deepest
trench, the Mariana Trench. On its maiden voyage the ROV was
deployed to the Challenger Deep, but was unable to move across
the seafloor because of the difficulty in managing its tether.
Essentially, it performed no better than the Trieste, which
got there first with two observers.
Unobtrusiveness
Fish
habitat studies require unobtrusive presence and the capability
sometimes to be able to observe from a silent and dark vantage
point. The slightest movement of an ROV is translated to its
tether and propagated along the tether's length. A submersible
can maintain station or be set to move nearly imperceptibly
slowly and soundlessly across the seafloor. A submersible
can essentially become part of a reef and observations (even
hand feeding of fish at bait stations) can take place unobtrusively.
Reliabilty
Frequent
recertifications of occupied vehicles makes them reliable
platforms. During his Midway Expedition when it came time
to lower the ROV into the water Bob Ballard was heard to comment
to the effect that "these things always break down." The ROV
he was using did fail at first, though as soon as replacement
parts arrived, Bob, as usual, succeeded in his quest and found
the USS Yorktown. Alvin's remarkable success record stems
from the fact that basically the sub has been in use for many
years and the bugs have been worked out. It is an incredibly
reliable work-horse, but it could be much more versatile with
the improvements envisioned by the NDSF.
Capacity for Outreach, Education, and Recruitment
The
best way to communicate the excitement of scientific discovery
to the people who ultimately fund our efforts, the pubic,
is to get them to see our science through our eyes. If there
is a reason for them to want to do so, if our eyes have looked
out the view port of a submersible, the task is much easier.
Human beings will identify with a person more readily than
with a robot, with an astronaut on EVA more readily even than
with the popular Mars Rover. Recruiting youngsters to become
the scientists of the future is more effective if they know
they can share personally in the goal of discovery.
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