Salinity substandard

All bench salinometers must be standardized with SSW. While strongly diseouraged for achieving WOCE standards in salinity, substandards may be used together with SSW to control the stability of the salinometer if less than the best aehievable accuracy is acceptable in... 

Only lAPSO recognized SSW provides a reliable standard for conductivity ratio measurements. It should be used to standardize each bench salinometer before being used for sample salinity measurements and to detect and eventually trace any drift. The use of so-called substandards for standardization is not recommended, as it will significantly decrease accuracy (see Section 3.5.7 for exceptions if a decrease in accuracy is acceptable). 

Immediately after the salinometer has been standardized with SSW (see Sections 3.5.3 and 3.5.4 for the AUTOSAL and the RSIO, respectively), the saUnities of three substandard bottles are measured successively. If each salinity differs from their average by less than the accuracy that is required for individual samples during the cruise, the substandard is accepted, with the average as the salinity of the substandard and the maximum difference between the three individual substandard sample salinities as its uncertainty. 

Individual substandard samples then serve to identify any drift in the salinometer calibration. If a substandard measurement differs by more than the substandard s uncertainty from its estimated salinity, a second substandard sample is taken for control. If the second value is outside the uncertainty interval as well, a SSW sample is measured for control of any instrumental drift within the required accuracy. 

If an AUTOSAL is operated under otherwise WOCE conditions (see Section 3.5.4), the accuracy for individual salinity samples can still be of the order of 0.002 when substandard samples instead of SSW are used to identify instrumental drifts. For the RSIO, it can be better than 0.01 depending on the operating conditions. 

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