Sometimes there are different terms which mean the same thing. Turbidity is a quantity measured by optical back-scatter of light and OBS stands for Optical Back-Scatter. TSS or Total Suspended Solids is also a quantity measured using optical back scattering.

Turbidity and TSS are essentially the same parameter. Although turbidity purports to measure approximately the same water quality property as TSS, the latter is more useful because it provides an actual weight of the particulate material present in the sample. The relationship between turbidity and TSS (total suspended solids) depends on the nature of the solids, but all turbidity sensors measure optical back scatter.

Here is the description from the Seapoint site:

“The Seapoint Turbidity Meter is a very low-power, miniature sensor that detects light scattered by particles suspended in water, generating an output voltage proportional to turbidity or suspended solids.”

And here is the description from the D&A site:

“The OBS®-3+ sensor measures suspended solids and turbidity by the optical back-scatter method (ASTM 6677). It features a compact micro probe that responses almost linearly over a 1000-fold change in sediment concentration (SSC) and turbidity.”

It amounts to exactly the same thing. The responsibility for calibration from turbidity to TSS in either case rests with the user.