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Section 8. Factors Affecting OBS

Response

This section summarizes some of the important factors that affect OBS-3A

measurements and shows how ignoring them can lead to erroneous data. If you

are certain that the characteristics of suspended matter will not change during

your survey and that your OBS was factory calibrated with sediment from your

survey site, you only need to skim this section to confirm that no problems

have been over looked.

8.1 Particle Size

The size of suspended sediment particles typically ranges from about 0.2 to

500μm in surface water (streams, estuaries and the ocean). Everything else

being equal (size, shape, and color), particle area normal to a light beam will

determine the intensity of light scattered by a volume of suspended matter.

Results from laboratory experiments and natural material support this and

indicate a wide range of backscatter associated with very fine mud and coarse

sand (about two orders of magnitude). Laboratory tests with coarse silt to

medium sand material show that sensitivity changes by a factor of about 3.5

(see FIGURE 8.2-1). The significance is that size variations between the field

and laboratory and within in a survey area cannot be ignored.

10 100 1000 10000 100000

Sediment Concentration (mg/l)

100

1000

10000

OBS Signal (mV)

Clay

Silt

Sand

FIGURE 8.1-1. Response to Sand, Silt and Clay

8-1

1 2 ... 42 43 44 45 46 47 48 49 50 51 52 ... 57 58

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Campbell OBS-3A Especificaciones Pagina 47