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Bathymetric Data from Waverunners
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Project scientists launch a modified
waverunner into the surf off Washington state. The GPS antenna can be seen
at the rear of the boat on top of a yellow box that contains the computer.
The computer screen on the handle bars aids the driver in navigation.
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For the past six months, we have been building and testing a new system to
collect bathymetric data in energetic, nearshore environments. Based on a
system developed by Oregon State University, our system is comprised of a
waverunner, which we have equipped with an echo sounder, GPS receiver and
antenna, and onboard computer running navigation software. The waverunner
is a Yamaha Wave Venture 700, which is large, powerful, and stable. The echo
sounder is an Oceandata Bathy 500, from which we stripped the paper recorder
and mounted the acquisition and processing boards in a waterproof box underneath
the seat. For precise horizontal and vertical positioning, we operate a Trimble
GPS receiver in Real-Time-Kinematic (RTK) mode. The GPS antenna is mounted
on the waverunner directly above the echo sounder. The GPS receiver is enclosed
in a waterproof box and stored underneath the seat. The GPS base station is
set up on a benchmark on land to provide a land-based vertical datum. The GPS
and echo-sounder data are delivered to the navigation software, Hypack, which
is running on a Libretto laptop computer also stored beneath the seat.
A monitor is housed in a waterproof box and mounted above the handlebars,
along with a waterproof keypad. The entire system is run by two 12-volt
batteries, which are also housed in a waterproof box and attached to a mount
on the back of the boat.
Three-dimensional model of nearshore sea floor off
Oysterville, Washington, derived from data collected by the waverunner. Elevation
is relative to North American Vertical Datum of 1988 in meters. Lateral distance
is relative to North American Datum of 1983 in meters. Northing and easting are
ways of describing latitudinal and longitudinal differences among data points,
respectively.
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A waverunner is the optimal boat for collecting nearshore bathymetry through
the surf zone. The boats operate with a jet-propulsion system, so they are
safer and have a shallower draft than a propeller-driven system. The boats
are extremely maneuverable, and, best of all, they can be easily righted
after they flip over (I know from personal experience!). The echo sounder
operates at 8 Hz and the GPS at 5 Hz, so surface waves are easily resolved
and accounted for in the data. Getting through the waves as they are breaking
in the surf zone is another matter.
Many people helped assemble this new data-collection system. Jamie MacMahan,
a Ph.D. student at the University of Florida working under a cooperative
agreement with the USGS, was responsible for integrating all of the components
of the new system. Jamie worked closely with Peter Ruggiero from the Washington
Department of Ecology (DOE) and Guy Gelfenbaum from the Menlo Park office to
design the system. We had lots of advice and even some help from Dave Wegener,
Phil Thompson, Mark Hansen, Keith Ludwig, and Terry Kelley from the St. Petersburg
Field Center, and Jessica Cote from the Woods Hole Field Center. Dave and Phil
were also recruited as field operators to check the boats for safe operation.
After a three-day comparative test in South Carolina, the waverunners were
delivered to the Washington coast for the summer field season. As part of the
Southwest Washington Coastal Erosion Study, the waverunners have been working
all summer collecting nearshore bathymetry across the 165-km-long Columbia River
littoral cell. Peter Ruggiero is responsible for the data collection, and, along
with Jamie MacMahan, has been assisted in the field this summer by Troy Warnick,
Josh McInnis, and Emily Lindstrum from DOE, and by Guy Gelfenbaum and Britt
Argow from Menlo Park. Bathymetric data are being collected in cross-shore
profiles from mean sea level out to depths of 11 to 12 m. In selected areas
within each sub-cell, profiles are spaced 200 m apart and are gridded to produce
3-D bathymetric surface maps. Between these surface maps, profiles are collected
every 1 km. Thanks to small swell (1-2 m, 7-9 s) and light winds (< 20 knots),
the field crew has collected over 125 profiles, and they are still going strong.
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September 1999
in this issue:
cover story:
Seeing the Bottom
Bathymetric Data: Waverunners
Sediment Database
Mamala Bay Web Site
Hurricane Camille
DOI Environmental Award
Hein Elected IMMS President
Robbins Attends FWC Ceremony
Visitors
September Publications List
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U. S. Department of the Interior | U.S. Geological Survey
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