OBS-3A Turbidity and Temperature Monitoring System
10.1 Particle Size
The size of suspended sediment particles typically ranges from about 0.2 to
500 µm in surface water (streams, estuaries and the ocean). Everything else
being equal (size, shape, and color), particle area normal to a light beam will
determine the intensity of light scattered by a volume of suspended matter.
Results from laboratory experiments and natural material support this and
indicate a wide range of backscatter associated with very fine mud and coarse
sand (about two orders of magnitude). Laboratory tests with coarse silt to
medium sand material show that sensitivity changes by a factor of about 3.5
(see FIGURE 10-1). The significance is that size variations between the field
and laboratory and within in a survey area cannot be ignored.
10
100
1000
10000
100000
Sediment Concentration (mg/l)
100
1000
10000
OB
S Si
gnal (m
V
)
Clay
Silt
Sand
FIGURE 10-1. Response to sand, silt and clay
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