| In most applications, the
answer is yes. This is because the window of an OBS
sensor must remain clean for the sensor to accurately measure
light scattering. Any material that buildups
on the window will change how the sensor “sees”
the sample through its window, and depending on whether the
sensor detects more or less light, it will indicate more or
less turbidity or suspended sediment. Chemical films, biological
growth, and dirt all affect sensor accuracy. Chemical films
look like the left hand photo shown below, which produced the
apparent decline in background turbidity shown on the chart.
The film was a tannin-based compound common in streams and swamps.
|
|
Barnacle
growth on moored OBS sensors is very common in a shallow marine
environment. The right hand photo shows barnacle
growth over the IRED and photodetectors of an OBS sensor moored
off the California coast. The barnacles obscured the light
emitter and produced declining turbidity. Fouling does not
always result in an apparent decline in turbidity. For example,
rapid algal growth on an OBS sensor in Tampa Bay caused turbidity
to increase because algae grew into the sample volume and
reflected light into the photodetectors and this created a
turbidity-like signal. The resulting effects were both severe
and rapid in onset (~ 1 week).
|
|
)
