Campbell Scientific OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors - Manual (Page 38)

OBS-3+ and OBS300 Suspended Solids and Turbidity Monitors
organic matter and interference from these materials can therefore be ignored
most of the time. One notable exception is where biological productivity is
high and sediment production from rivers and re-suspension is low. In such an
environment, OBS signals can come predominately from plankton.
11.8 Biological and Chemical Fouling
Sensor cleaning is essential during extended deployments. In salt water,
barnacle growth on an OBS sensor can obscure the IR emitter, the detector, or
both and produce an apparent decline in turbidity. Algal growth in marine and
fresh waters has caused spurious scatter and apparent increases of OBS output.
The reverse has also been noted in fresh water where the signal increases after
cleaning the sensor window. Prolonged operation in freshwater with high
tannin levels can cause a varnish-like coating to develop on an OBS sensor that
obscures the IR emitter and caused an apparent decline in turbidity. Cleaning
algal and tannin accumulation off OBS sensors is required more often during
the summer because warm water and bright sunlight increase biological and
chemical activity.
Campbell Scientific sells two wipers from a third-party manufacturer: the
Hydro-Wiper C with its own controller, or the Hydro-Wiper D that is
controlled by a datalogger.
12. References
Bohren, C.F. and D.H. Huffman. Absorption and Scattering of Light by Small
Particles, John Wiley & Sons, New York, 1983.
Downing, John. 2006. Twenty-five Years with OBS Sensors: the Good, the
Bad, and the Ugly. Continental Shelf Research 26, 2299-2318.
Downing, John, Turbidity Monitoring, Chapter 24 In: Environmental
Instrumentation and Analysis Handbook, John Wiley & Sons, New York, pp.
511-546, 2005.
Downing, John and R.A. Beach. 1989. Laboratory apparatus for calibrating
optical suspended solids sensors. Marine Geology 86, 243-249.
Lewis, Jack. 1996. Turbidity-controlled Suspended Sediment Sampling for
Runoff-event Load Estimation. Water Resources Research, 32(7), pp. 2299-
2310.
Sadar, M. 1998. Turbidity Standards. Hach Company Technical Information
Series – Booklet No. 12. 18 pages.
Sutherland T.F., P.M. Lane, C.L. Amos, and John Downing. 2000. The
Calibration of Optical Backscatter Sensors for Suspended Sediment of Varying
Darkness Level. Marine Geology, 162, pp. 587-597.
U.S. Geological Survey. 2005. National Field Manual of the Collection of
Water-Quality Data. Book 9, Handbooks for Water-Resources Investigations
Zaneveld, J.R.V., R.W. Spinrad and R. Bartz. 1979. Optical Properties of
Turbidity Standards. SPIE 208 Ocean Optics VI. Bellingham, Washington, pp.
159-158, 1979.
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