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Instrument Calibrations and Water Column Profile Surveys of a
Grace M. Battisto, Virginia Institute of Marine Science (VIMS)
This work is being conducted in support of an ongoing investigation on
sediment dispersal and evolution of a mixed-sediment disposal mound by the
US Army Corps of Engineers. Repetitive water column surveys, suspended
sediment concentration samples and bottom sediment grabs are being collected
for calibration of Acoustic Doppler Current Profilers (ADCP) and Optical
Backscatter Sensors (OBS) deployed by Carl Miller of the USACE Field Research
Facility on the site of the disposal mound and immediate vicinity. The Virginia
Institute of Marine Science, College of William and Mary, under the direction of
Grace M. Battisto, will be performing the work.
Scope of Work
Preliminary Bottom Grab and Suspended Sediment Results
Profiler - The profiler allows all the instruments (LISST, OBS, ADV,
CTD, and compass) to be lowered through the water column at the same rate.
LISST - Laser in-situ Scattering Transmissometer
- The LISST is used to measure the grain size distribution of suspended
sediment from 5 to 500 microns (silts, clays, and fine sands).
CTD Gauge - The CTD measures the conductivity, temperature, and depth at
the sensor height as the profiler is lowered through the water column. The conductivity and
temperature are used to determine the salinity at each depth.
OBS - Optical Backscatter Sensor - Backscattered light within the OBS sampling
volume is used to estimate suspended sediment concentration at the sensor height.
ADV - Acoustic Doppler Velocimeter - Sound emitted by an Acoustic transmitter
is backscattered off of suspended particles within the sampling volume and detected by three
receivers to estimate water velocity at a single location.
ADCP - Acoustic Doppler Current Profiler - The ADCP measures the water
velocities in 0.25 m (0.8 ft) bins from just below the instrument to the bottom of the water
column, when mounted on a vessel.
Smith-Mac Sediment Grab - Bottom sediments collected using the Smith-Mac allow
coupling of sediment type and porosity (trapped water) with the water column properties measured
with the ADCP and profiler.
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