Campbell Scientific OBS-3A Turbidity and Temperature Monitoring System - Manual (Page 69)

OBS-3A Turbidity and Temperature Monitoring System
10.7 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 and/or detectors
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 coatings to develop on an OBS sensor that obscure 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. See Section 9.6, Antifoulant Coatings, for alternatives to cleaning.
11. References
Conner, C.S. and A.M. De Visser. 1992. A Laboratory Investigation of
Particle Size Effects on an Optical Backscatterance Sensor. Marine Geology,
108, pp.151-159.
Downing, John and W.E. Asher. 1997. The Effects of Colored Water and
Bubbles on the Sensitivity of OBS Sensors. American Geophysical Union, Fall
Meeting, San Francisco, CA.
Downing, John and Reginald A. Beach. 1989, Laboratory Apparatus for
Calibrating Optical Suspended Solids Sensors. Marine Geology, 86, pp. 243-
249.
Gippel, C.J. 1995. Potential of Turbidity Monitoring for Measuring the
Transport of Suspended Solids in Streams. Hydrologic Processes, Vol.9, pp.
83-97.
International Standard ISO 7027. Second Edition 1990-04-15. Water Quality –
Determination of Turbidity. International Organization for Standardization.
Genève, Switzerland. 6 pages.
Lewis, Jack. 1996. Turbidity - Controlled Suspended Sediment Sampling for
Runoff-Event Load Estimation. Water Resources Research, Volume 32, No.
7, pp. 2299-2310.
Ludwig, K.A. and D.M. Hanes. 1990. A Laboratory Evaluation of Optical
Backscatterance Suspended Solids Sensors Exposed to Sand-Mud Mixtures.
Marine Geology, 94, pp.173-179.
Papacosta, K., J.A. Spair and M. Katz. The Rationale for the Establishment of
a Certified Reference Standard for Nephelometric Instruments. Advanced
Polymer Systems, Inc. Redwood City, CA.
Sadar, M. 1995. Turbidity Standards. Technical Information Series-Booklet
No. 12. Hach Company. Loveland, Colorado. 18 pages.
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