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Water Quality of San Francisco Bay
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Calibration of Optical Backscatter Sensor (OBS)

We determine the concentration of suspended particulate matter (SPM) in the water column using a submersible Optical Backscatter Sensor (OBS). The OBS operates by sending a beam of infrared light into the water, the beam is scattered by suspended particles and the OBS then measures the quantity of light that is reflected back to its sensor. The instrument is calibrated each sampling date by comparing the OBS values to collected water samples. We filter the water samples onto pre-weighed filters and re-weigh the filters after they are dried, the difference in weight is due to the SPM. This plot shows the agreement between the discrete (collected) SPM concentrations and those calculated from the OBS. The points on this plot represent all the measurements made in South Bay during 1996. The average deviation between calculated SPM from the OBS and measured/sampled SPM is 2.2 milligrams per liter, equivalent to a mean error of 8%.

See examples of SPM vertical profiles.

OBS Sensor Calibration Plot

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