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Frequently Asked Questions

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Software & Data Processing

The spike seen in the pump out phase is due to the commencement of flow and reagents/material that is outside the optical path initially but is swept through the optical path during flush out. The spike is accepted as normal behavior of the system and does not affect data quality.

Whether the tau correction is applied depends on where the system is being deployed.nnIf the system is to be used in shallow, coastal waters where large vertical gradients that change quickly are expected, the tau correction should be applied, as it accounts for the response time and puts the interface between two different water masses in the right place.nnIf the system is to be used in deep water (>200 m) where the vertical gradients are small, the tau correction should be turned off – in areas where the gradients are small, the calculation adds more noise.

CAPO4 is the phosphate concentration that the instrument reports as its measurement. CAPO4 is the calculated concentration of an ambient sample using the CAS slope, where CAS is the manufacturer’s scale factor, which is provided by Sea-Bird. nnVAPO4 is used in a QC process to monitor potential drift or spot pump failures or other mechanical problems. VAPO4 is the calculated concentration of an ambient sample using the VAS slope, where VAS is a variable slope calculated in-situ using the on board standard. VAS is only calculated during the Cal Spike frequency runs, used on subsequent samples between the Cal Spike. So, VAS and VAPO4 are not always good values and can affect whole groups of samples between the Cal Spike runs.nnThe calibration for CAPO4 does not include a variable ambient sample of unknown quantity as VAPO4 does.

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