Campbell Scientific OBS-5+ Sediment Concentration Monitor and Pressure Sensor - Manual (Page 49)

Appendix A. Turbidity Standards
We must emphasize that unlike SSC, which has physical units, turbidity values
(NTUs, FTUs, etc.) do not. Therefore, if you measure water turbidity to be 100
NTU, you cannot directly infer any physical quantities from it. Turbidity
values do not represent particular SSC values, indicate light levels at the
bottom of a stream, or quantify biological process’. Moreover, it is often
assumed that turbidity standards behave optically like sediment. This is
possible when the size, NIR reflectivity, refractive index, and shape of the
sediment and the turbidity standard are similar; this is an extremely rare
occurrence. For example, even the median diameters of the two approved
calibration standards differ by a factor of more that five and the shape of
SDVB and formazin particles also differ; see NTU-SSC relationships.
Reference:
John Downing. 2005. Turbidity Monitoring. Chapter 24 in: Environmental
Instrumentation and Analysis Handbook. John Wiley & Sons, Pages: 511-
546. 2005.
Sadar, M. 1998. Turbidity Standards. Hach Company Technical Information
Series – Booklet No. 12. 18 pages.
Papacosta, K. and Martin Katz. 1990. The Rationale for the Establishment of
a Certified Reference Standard for Nephelometric Instruments. In:
Proceedings, American Waterworks Assoc. Water Quality Technical
Conference. Paper Number ST6-4, pp. 1299-1333.
Zaneveld, J.R.V., R.W. Spinrad, and R. Bartz. 1979. Optical Properties of
Turbidity Standards. SPIE Volume 208 Ocean Optics VI. Bellingham,
Washington. pp. 159-158.
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