SandyDuck '97 Facts and Instrument Descriptions
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Participants: over 250
Organizations: 26 total, 22 US, 3 Canadian, 1 United Kingdom
Sponsors: US Army Corps of Engineers, Office of Naval Research, US Geological Survey
Sensors: over 400
Cables: 150 cables installed to connect sensors to the shore stations
Computers: 115 computers to collect, exchange and process data.
Portable Trailers 12
Different Investigations 30 (though they vary widely in size and complexity)
Years in Planning 7
SandyDuck '97 Schedule
15 June - 21 September 1997: Deployment of Instruments
22 September - 31 October 1997 Experiment
November 1997 Instrument removal
During SandyDuck, state-of-the-art instruments and technologies will be used to make measurements of the coastal environment under
all conditions. Some of the unique instruments being used include:
Fiber Optic Backscatter Sensors (FOBS)- A major problem with most instruments that measure sediment movement is that the
physical size of the sensor is much larger than sand grains. The innovative FOBS solves this problem by using small optical fibers and
light to measure the movement of individual sand grains.
Acoustic Instruments - a whole range of new oceanographic instruments are using underwater acoustics to make new or better
observations. Some of the acoustic instruments being used are:
- Acoustic Altimeters - In the past, our knowledge of how much the beach eroded was gained by comparing maps of the nearshore
zone collected before and after a storm. Although this provides a measure of the amount of sand eroded from the beach and
deposited offshore, it doesn't provide any information on how the sand actually moved. During SandyDuck acoustic altimeters
(sonars) will be deployed in shore-perpendicular and shore-parallel lines. Each sonar will continuously record the changing height
of the bottom under it and collectively they will provide accurate maps of ocean bottom as it changes. In one investigation a line of
altimeters placed very close together (called a Multiple Transducer Array) will be used to make fine-scale measurements of the
movement of ripples on the seafloor.
- Current meters - Unlike most current meters which interfere somewhat with the water flow by their very presence, acoustic
current meters use sound to measure the water movement some distance away. This improvement helps collect better and more
accurate current measurements.
- Side-scan Sonars - Like the one used to locate the Titanic, Side-scan sonars of various types will be used to literally use sound to
paint pictures of the ocean bottom as it changes. Of particular interest are the development and movement of "megaripples", large
ripples in the sediment that appear to be of great importance in the movement of sediment. Small side-scan sonars will be
permanently placed underwater and used to observe megaripples as they move around. A larger system will be mounted on the
CRAB and used to provide an overall map of where the megaripples are.
- Secscan Sonars - This sonar is capable of looking sideways through the water and measuring the currents. Two of these sonar
devices will be installed offshore in 6.5 m (20 ft) water depth in such a way as to develop a map of the currents in a 200x500 m
(650x1600 ft) region close to the shore. These measurements will complement the point measurement of the other current meters
and should provide some of the most detailed observations of rip currents ever collected.
- Acoustic Concentration Profiler - Like the acoustic current meters, the Acoustic Concentration Profiler is able to measure
without intruding into the flow. It detects the amount of sediment being moved and can also provide a measure of how the
concentration of sediment varies with height above the bottom.
Video Cameras - Nearly every wave passing through the SandyDuck experiment will be recorded by video cameras located on special
towers. Although video cameras are no in themselves unique, by cleverly processing the collected images, SandyDuck scientists will
be able to map the ocean bottom, measure surface currents, measure waves, and identify important motions in the coastal ocean that
are difficult to observe with the naked eye, or measure with conventional instruments.
Radars - The same type of radar systems used to locate ships at sea can also be tuned to make measurements of waves and currents
and to remotely sense the underlying shape of the nearshore bottom. Several marine radars will be used to complement the point
measurements of the other instruments. In a completely different application, Ground Penetrating Radar will be used to map out the
geologic structure of the beach.
Pressure Sensors - Pressure sensors placed underwater measure the weight of the water above and are used to measure waves and
water levels. Many pressure sensors will be installed in different configurations called arrays. Three large arrays of pressure sensors
and several smaller ones will be used to obtain detailed information about the waves, including their direction of approach to the
shore. Pressure sensors will also be used to provide a precise measure of the water level close to shore, useful in measuring the storm
surges associated with hurricanes and passing nor'easters.
Hydrophones - Hydrophones are underwater microphones which will be used to listen to wave breaking and to measure the natural
sounds in the ocean. These will also be installed in multiple hydrophone arrays.
Electromagnetic current meters (EMCM)- Though not as elegant as the newer non-invasive acoustic current meters, the
electromagnetic current meter has long been the workhorse of oceanographers trying to measure nearshore currents. These current
meters work on the principle that a conductor (the water) flowing through a magnetic field (generated by the current meter probe)
produces a voltage proportional to its velocity. Numerous EMCM will be deployed as part of multi-instrument packages.
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