Appendix E. Factors that Affect Turbidity and Suspended-Sediment Measurements
E-4
FIGURE E-4. Response of an OBS sensor to a wide range of SSC
E.5 IR Reflectivity—Sediment Color
Infrared reflectivity, indicated by sediment color, has a major effect on
sensitivity because with other factors remaining constant, it changes the
intensity of light scattering. Although turbidity sensors are color blind, tests
have shown that “whiteness”, color, and IR reflectivity are correlated. Calcite,
which is highly reflective and white in color, will produce a much stronger
turbidity signal on a mass-concentration basis than magnetite, which is black
and IR-absorbing. Sensitivity to colored silt particles varies from a low of
about one for dark sediment to a high of about ten for light gray sediment; see
FIGURE
. In areas where sediment color is changing with time, a single
calibration curve may not work. Resulting errors will depend on the relative
concentrations of colored sediments.
