a higher frequency, creating a much higher-resolution image.
With SAS, only one pass would be made, and the resolution
would be just as good if not better than the highest-resolution
side-scan image, all while covering hundreds of times more
bottom than the side-scan. The downside of SAS is cost and
size; even for a shallow-water version I was recently quoted
$160,000 for a 10-day search. That’s unaffordable for most
people (including me), but for institutions and those with deep
pockets, SAS is an incredibly useful tool — especially if it can
be combined with other search tools.
A magnetometer is similar to a compass in that it detects
the earth’s magnetic field, but a “mag” is infinitely more
sensitive. As with many search tools, a mag is towed behind a
boat while an operator watches a screen for variations in the
magnetic field. As the fluctuations get stronger, the operator
can follow the anomaly and identify it using sonar, side-scan
or some other device capable of “seeing” the bottom.
An interesting question might arise if you come to an
area with a magnetic anomaly but without any visible sonar
evidence. This is where sub-bottom profilers may be very
useful. Designed to characterize layers of sediments sometimes
hundreds or thousands of feet down, these tools are, at least in
theory, incredibly handy when searching for buried shipwrecks.
Unfortunately, they have not yet lived up to the hype, but there
is still hope that sub-bottom profilers one day will provide
detailed images of wrecks that lie beneath the sediment.
Another instrument commonly used by wreck hunters is a
fish finder. Fish finders emit and detect reflected sound waves
and display a simple representation of the water column and
the bottom under the boat. Fishermen use them for the obvious
reason, and boaters use them to ensure there is enough water
beneath the keel. Dive operators often watch the fish finder for
the bump on the bottom that signifies a wreck, and crews of
wreck hunters often keep a pair of eyes glued to the fish finder
as they “mow the lawn,” searching the ocean floor.
Mags, side-scan and fish finders have been the principal tools
used to find almost all shipwrecks that have been discovered.
The common factor in all these tools is the human interface.
From running boats to watching cables to putting eyes on the
screen, human control has been the connective tissue that
allows all these technologies to work. However, like the rest
of society, ocean exploration is undergoing a quantum leap in
technology, and the way we find wrecks is beginning to change.
This change is largely being fueled by the use of robotics,
especially autonomous underwater vehicles (AUVs).
AUVs
AUVs represent a great technological leap forward in ocean
exploration and shipwreck hunting. They have been in
development since the 1960s but have only recently, with the
creation of remote environmental monitoring units (REMUS)
at Woods Hole, come to the forefront of exploration. REMUS
vehicles look like torpedoes, but instead of carrying explosives
these AUVs carry various arrays of remote-sensing tools (side-
scan, multibeam, sub-bottom profilers and more) along with
cameras and lights. An AUV is programmed for a mission
and then deployed off the stern, which leaves researchers on
the ship free to perform other tasks. While on its mission, an
AUV uses internal sensors and sonars to avoid objects and
follow the contours of the bottom.
Such capabilities are very exciting for those whose
searches take place in areas with canyons or extensive
coral formations. Side-scan and other towed sensors can
be stymied by high-relief bottom topography, but REMUS
vehicles are able to get inside these difficult areas, making
searching them incredibly more efficient. REMUS AUVs
have already mapped miles of ocean around the Titanic,
found a lost Air France plane off Brazil and found countless
shipwrecks across the world. Although AUVs can search
the bottom based on preprogrammed missions, data still
must be downloaded and interpreted when the units surface.
Depending on the data, this may take hours, days or even
months. Humans are not out of the game quite yet.
Archaeologist Brendan Foley uses AUVs to help find
shipwrecks and shed light on ancient trading practices.
Foley is part of the upcoming generation of maritime
archaeologists that embraces the use of technology in the
search for lost shipwrecks. Not only has he successfully used
AUVs in his hunt for Minoan shipwrecks in Greece, he is
also one of the few in the archaeological community using
closed-circuit rebreathers for exploration.
The Future of Exploration
Today we are experiencing something of a renaissance in
the world of science and exploration. Most of us are used
to seeing the government fund or encourage many of the
technologies used for research expeditions. However, as
government coffers run dry, agencies such as the National
Science Foundation (NSF) and the National Oceanic and
Atmospheric Administration (NOAA) are cutting back on
what they are able to spend to fund these projects.
Harkening back to the days of Michelangelo, when well-
off patrons subsidized many of the world’s greatest artists,
a portion of the world’s wealthiest people have taken a
profound interest in ocean exploration and shipwrecks they
believe to be culturally significant. Across the world, there
is now a fleet of “research yachts” that carry equipment
such as submarines and AUVs with advanced scientific and
imaging capabilities. Many of these new patrons to science
and archaeology are beginning to fund expeditions that,
at least in part, involve shipwreck hunting. Although the
government is not funding these endeavors to the extent it
once was, governmental agencies including NOAA and the
National Park Service (NPS) continue to document what
exists along our coasts and in our lakes and rivers.
As technology gets better and cheaper, it’s easy to imagine
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fall 2012