Figure D9. ADP transects September 2001
Water samples
Two near-bottom water samples were collected in the vicinity of the two
tripod stations on 12 May at 0.5-m elevation above bottom. The samples were
analyzed for Total Suspended Solids (TSS) to document sediment concentration
in the water column during a flood tide.
Calibration of optical backscatter sensors
All OBS-3 sensors deployed with Hydra systems were calibrated for
suspended sediment concentration. OBS signals are recorded by the Hydra
system in "counts" ranging from 100 to 65,000, which must be converted to the
desired units during post-processing. Calibrations were performed in a turbidity
chamber following the specifications recommended by the manufacturer.
Instrument gains were set prior to deployment using tap water (minimum) and
800 nephelometric turbidity units (ntu) Formazin standard solution (maximum).
OBS deployed on the SIDSEP were calibrated over a range of 0 to 32 g/L at four
concentrations (2 g/L, 8 g/L, 16 g/L and 32 g/L) with sand collected from north
beach near mllw. OBS deployed on the jetty tripods were calibrated over a range
of 0 to 24 g/L range at five concentrations (2 g/L, 4 g/L, 8 g/L, 16 g/L and
24 g/L) with sediment from the grab sample obtained near sta OS 6.
OBS calibration data (number of points = 1028 at 4 Hz) were extracted from
the Hydra files and average, standard deviation, minimum, maximum and
coefficient of variation were computed and the series plotted for a visual quality
check. Coefficient of variation was typically 10 percent and not more than 15
percent for acceptable calibration results. Second-order polynomial curves fit to
D13
Appendix D Field Data Collection
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