6 4 YACHTING JANUARY 2018INSIGHTS ELECTRONICSM
a r i t i m e w i s d o m holds that there are two kinds of boaters:
those who have found the bottom, and those who will. I joined
the former club in 1988 while cruising the Chesapeake Bay with
my dad and his buddies. We were fl ying our brightly colored
spinnaker when Windancer — my parents’ C&C 37 — “discov-
ered” an uncharted sandbar. Dousing the kite wasn’t problematic, but refl oating
our vessel involved the crew dangling from the starboard shroud and rocking
her keel free. We eventually found deeper soundings, but not before I learned
some creative expletives from my dad, who wasn’t thrilled with his brand-new-
but-already-obsolete paper charts. As we learned that day, sandbars sometimes
move faster than survey crews. ¶ The National Oceanic and Atmospheric Ad-
ministration is using forward-leaning technology to close that knowledge gap.
One tool NOAA’s Remote Sensing Division uses to collect data is light detection and ranging laser-pulse technology ( lidar).heights of roughly 1,000 to 2,000 feet.
W hile previous-generation lidar equip-
ment could collect “a few” data points
per square meter, Imahori says, the Riegl
collects as many as nine points per me-
ter in shallow water (down to 56 feet).
“It’s an immense amount of detail,”
Imahori says, adding that lidar works
in places where NOA A’s vessels previ-
ously found it diffi cult to operate. The
technology works best, she says, with
bright, light-ref lective bottoms and
calm, crystal-clear waters.
NOAA’s King Air, meanwhile, carries
two 80-megapixel cameras. One collects
“red-green-blue” color imagery, the other
near-infrared imagery. Both are accurate
to 35 centimeters from 10,500 feet. This
ultra-high-resolution imagery is used for
photogrammetry, the science of taking
precise measurements using photography.
Given the speeds of these aircraft,
when compared with a slower, ship-towed
sonar array, the sensing division can
cover ground quickly, a critical ability
when collecting post-hurricane data.
However, given the sheer volume of
nearshore bathymetric data that must
be compiled, Imahori says, the division
also contracts work out to commercial
survey companies and is researching the
use of eBee drones. The drones would
collect aerial photography to produce
3D models accurate to 3 centimeters.
While the sensing division is doing its
work, the hydrographic division devel-
ops project instructions for in-house and
third-party survey missions across 3.4
million square miles. It then takes that
data — along with sensing-division data
— and reviews it for quality-control be-
fore applying it to offi cial NOAA products,
including the bathymetry database or
nautical charts. One of the hydrographic
division’s most important resources is
its Hydrographic Health Model, which
factors the age, acquisition technique
and seafl oor type of all existing NOAANOA A produces and maintains all offi cial
cartography for U.S. waters, including
a staggering 95,000 miles of shoreline.
The agency’s traditional methods for
collecting bathymetric measurements
work well for soundings deeper than
30 feet, but recent years have seen the
rise of remote-sensing technologies,
which allow NOA A to acquire precise,
high-resolution bathymetric data for
shorelines and nearshore waters.
“We maintain the shoreline on NOA A
nautical charts, which is considered the
nation’s legal shoreline,” says Gretchen
Imahori from NOA A’s Remote Sensing
Division, whose tools include light
detection and ranging laser-pulse
technology (lidar). “Aside from being
able to derive our shoreline from our
topographic-bathymetric lidar data, it
also allows us to help update nearshore
and back-bay areas on NOA A charts. It
is more effi cient for us to survey these
areas, and safer than sending in launch-
es with sonar.”
NOAA employs its remote-sensed data
to update its nautical charts quickly and
accurately, and to support emergency
eff orts after major storms (see sidebar).
The agency’s charts are available to all
mariners to download for free, and vir-
tually all third-party cartography com-
panies use NOAA data as the U.S. base
maps underpinning their proprietary
off erings. The sensing division, Imahori
says, works closely with NOAA’s Hydro-
graphic Surveys Division and Marine
Chart Division to coordinate survey-col-
lecting eff orts. The sensing division uses
two specially equipped planes to collect
shoreline, nearshore and back-bay survey
data, while the hydrographic division
surveys waters deeper than 13 feet.
NOA A’s DHC-6 Twin Otter aircraft
serves as the slow, low-fl ying operat-
ing platform for the agency’s Riegl VQ-
880-G airborne laser-scanning system.
The Riegl lidar uses a green laser in an
elliptical scanning pattern to measure
the distance to a surface from surveyPOST-STORM SURVEY WORK
Given the number and intensity
of hurricanes that hammered the
Caribbean and U.S. mainland this
past autumn, there’s zero chance that
harbors and shipping lanes remained
unscathed. However, NOAA has a
solution to the problem of mariners
having out-of-date charts. Accord-
ing to Tara Wallace, chief of NOAA’s
Nautical Data Branch, the agency
maintains six mobile navigation teams
that oversee 175 major ports nation-
wide. These teams act like bathymet-
ric fi rst responders who negotiate
storm-tossed harbors, do survey work
and help the harbors reopen.