E-1
Appendix E. Factors that Affect
Turbidity and Suspended-Sediment
Measurements
This appendix summarizes some of the factors that affect OBS measurements
and shows how ignoring them can lead to erroneous data. If you are certain that
the characteristics of suspended matter will not change during your survey and
that your OBS was factory-calibrated with sediment from your survey site, you
only need to skim this section to confirm that no problems have been
overlooked.
E.1 Particle Size
The size of suspended-sediment particles typically ranges from about 0.2 to
500
μm in surface water (streams, estuaries
, and ocean). With size, shape, and
color remaining constant, particle area normal to a light beam will determine
the intensity of light scattered by a volume of suspended matter. Results of
tests with sediment shown in FIGURE
indicate a wide range of sensitivity
is associated with fine mud and coarse sand (about two orders of magnitude).
The significance of these results is that size variations between the field and he
laboratory and within a survey area during monitoring will produce shifts in
apparent TU and SSC values that are unrelated to real changes in sediment
concentration.
10.0
100.0
1000.0
Median Particle Size (D
50
)
0.01
0.10
1.00
O
B
S
S
e
n
s
iti
v
ty
,
S
(m
V
p
e
r
m
g
l
-1
)
S ~ 1/D50
FIGURE E-1. Normalized sensitivity as a function of grain diameter
