Campbell Scientific OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors - Manual (Page 36)

OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors
FIGURE 11-4. Response of an OBS sensor to a wide range of SSC
11.5 IR Reflectivity—Sediment Color
Infrared reflectivity, indicated by sediment color, has a major effect on OBS
sensitivity because with other factors remaining constant, it changes the
intensity of light scattering. Although OBS 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
OBS 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 11-5. 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.
26