3. The SPM samples collected by the Niskin rosette water sampler are heavily biased towards calm conditions as it may be unsafe to take water samples during storm conditions. In contrast, the turbidity tank experiences a wider range of suspended sediment concentrations which may show any non‐linear response that some OBS sensors can demonstrate (but generally at higher concentrations than found during this work).


4.


In poor weather conditions, the vertical movements of the CTD/rosette system can vary by several metres as waves pass under the ship. This can result in water samples taken at (say) either 2m above the seabed or 4m. The Booner tube samples collect sediment continuously.


5.


It is well known that collecting either very heavy (large) or very light (small with slow settling velocity) particles is intrinsically difficult with CTD/rosette systems. The turbidity tank methodology is less sensitive to particle size changes in the water column.


6. Although Day grab sea bed samples were taken, the particle size distributions observed were significantly different to the sediment collected by the Booner tubes and was not therefore used for turbidity tank calibration.


In spite of the significant advantages of using Booner tube samples in a calibration tank, several issues arose with some of the particular samples collected during this project. The most noticeable concern was the sediment samples collected in June, July and September. The samples were very dark and contained significant quantities of decayed organic matter.


Following each turbidity tank calibration, suspended sediment concentration was plotted against OBS analogue input ADC count recorded by the AWAC (see figure 10 for an example).


EAST ANGLIA THREE – CEFAS FINAL TECHNICAL REPORT


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