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www.ocean-sci-discuss.net/6/2461/2009/
doi:10.5194/osd-6-2461-2009
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About uncertainties in practical salinity calculations
French Hydrographic and Oceanographic Service (SHOM), CS 92803, 29228 Brest Cedex 2, France
Abstract. Salinity is a quantity computed, in the actual state of the art, from conductivity ratio measurements, knowing temperature and pressure at the time of the measurement and using the Practical Salinity Scale algorithm of 1978 (PSS-78) which gives practical salinity values S. The uncertainty expected on PSS-78 values is ±0.002, but nothing has ever been detailed about the method to work out this uncertainty, and the sources of errors to include in this calculation. Following a guide edited by the Bureau International des Poids et Mesures (BIPM), this paper assess, by two independent methods, the uncertainties of salinity values obtained from a laboratory salinometer and Conductivity-Temperature-Depth (CTD) measurements after laboratory calibration of a conductivity cell. The results show that the part due to the PSS-78 relations fits is sometimes as much significant as the instruments one's. This is particularly the case with CTD measurements where correlations between the variables contribute to decrease largely the uncertainty on S, even when the expanded uncertainties on conductivity cells calibrations are largely up of 0.002 mS/cm. The relations given in this publication, and obtained with the normalized GUM method, allow a real analysis of the uncertainties sources and they can be used in a more general way, with instruments having different specifications.
Discussion Paper (PDF, 591 KB) Interactive Discussion (Open, 6 Comments) Manuscript under review for OS
Citation: Le Menn, M.: About uncertainties in practical salinity calculations, Ocean Sci. Discuss., 6, 2461-2485, doi:10.5194/osd-6-2461-2009, 2009. Bibtex EndNote Reference Manager XML
