About the of calibration uncertainty of conductivity sensors of CTD-probes «Sea Bird» in measurements and in practical salinity calculations

The factors determining combined standard uncertainty (CSU) in the calibration of precision CTD probes conductivity sensors are considered. Calculation of standard uncertainties (SU) of individual components is done and analysis of their contribution into CSU calibrations of conductivity sensors of five basic models CTD-probes «Sea Bird» is done. It is shown that expanded CSU calibration of conductivity sensors of CTD-probes reviewed models at any points in the range from 53 mS/cm till 27 mS/ cm will not exceed (2.2÷1.0)·10^–3 mS/сm; relative extended CSU calibration of these sensors will not exceed 4.2·10^–5 and will be determined by CSU value of reference conductivity cell calibration. Expanded CSU of salinity US determination according to СТp measurements dat at coverage factor К=2 will be equal to 0.0031÷0.0034 upon contribution of CTD-probe CSU calibration at the level 0,0007÷0,0010 for 31≤S≤39; –2≤T≤25 °С; 27≤С≤53 mS/cm and 0≤р≤10000 dbar. According to experimental data the characteristics of sensitivity coefficient ∂f/∂С dependencies of standard deviations of input frequency s( f_i) and sensor readings s(Cз_i) from sea water electrical conductivity are calculated. Analysis of calibration characteristics of conductivity sensors temporal drift between calibrations is conducted.

1. Levashov D.E. 2003. Tekhnika ekspedicionnyh issledovanij: Instrumental’nye metody i tekhnicheskie sredstva ocenki promyslovo-znachimyh faktorov sredy [Facilities and technique for marine surveys: Instrumental methods and components for estimating the fishing-significant characteristics of water medium]. M.: Izd-vo VNIRO. 400 s.

2. Pohodun A.I. 2006. Eksperimental’nye metody issledovanij. Pogreshnosti i neopredelennosti izmerenij [Experimental research methods. Errors and measurement uncertainties]. Uchebnoe posobie. SPb: SPbGU ITMO. 112 s.

3. Ramazin A.N. 2016. Nekotorye nauchno-metodicheskie aspekty metrologicheskogo obespecheniya izmerenij elektroprovodnosti i temperatury morskoj vody s pomoshch’yu STD-zondov [Some scientific and methodological aspects of metrological supply of conductivity and sea water temperature measurements with CTD-probes] // Trudy VNIRO. T. 159. S. 167–182.

4. Ramazin A .N., Levashov D.E., 2016. Metodicheskie rekomendacii po kalibrovke i metrologicheskomu obespecheniyu izmeritelej parametrov vodnoj sredy [Guidelines for calibration and metrological support of measuring instruments for the parameters of the aquatic environment]. M.: Izd-vo VNIRO. 127 s.

5. Ramazin A.N. 2017. Raschyot pogreshnosti opredeleniya prakticheskoj solyonosti po dannym STr-izmerenij [Error calculation of practical salinity determination according to the CTP-date measurements] // Sistemy kontrolya okruzhayushchej sredy. Sevastopol’: IPTS. Vyp.9 (29), S.7–18.

6. Ramazin A.N. 2018. Ocenka neopredelyonnosti kalibrovki i izmerenij datchikov temperatury CTD-zondov «Sea Bird» [Evaluation of calibration and measurement uncertainty of temperature sensors of CTD-probe “Sea Bird”] //Sistemy kontrolya okruzhayushchej sredy. Sevastopol’: IPTS. Vyp.14 (34), S.33–42.

7. Ramazin A.N. 2021. Ocenka neopredelyonnosti kalibrovki etalonnoj yachejki elektroprovodimosti kalibratora ST01 «Idronaut» «Ustanovki dlya izmereniya specific electrical conductivity morskoj vody VNIRO» [Evaluation of calibration uncertainty reference conductivity cell of calibrator СT01«Idronaut» “Installations for measuring specific electrical conductivity of sea water VNIRO”] // Trudy VNIRO. T. 184. S. 99-111.

8. Rekomendacii po standartizacii R50.01.097–2014. 2015. Statisticheskie metody. Primery izmerenij pri analize povtoryaemosti i vosproizvodimosti. [ISO/TR 12888:2011. Selected illustrations of gauge repeatability and reproducibility studies (IDT)]. M. Standartinform. 34 s.

9. Rukovodstvo po vyrazheniyu neopredelennosti izmereniya. 1999.Perevod s angl. pod nauch. red. prof. Slaeva V.A. SPb.: VNIIM im. D.I. Mendeleeva. 134 s. (Guide to the Expression of Uncertainty in Measurement. 1993. First edition. ISO, Switzerland. 101 pp.)

10. IOC, SCOR and IAPSO. 2010. The international thermodynamic equation of seawater — 2010: Calculation and use of thermodynamic proper-ties. Intergovernmental Oceanographic Com-mission, Manuals and Guides 56, UNESCO (English), 196 pp. http://www.teos-10.org/TEOS-10_Manual.pdf. 20.08.2019.

11. Menn M.L.2011.About uncertainties in practical salinity calculations // Ocean Science. Copernicus, V.7, рр. 651–659. https://www.researchgate.net/publication/307769547_About_uncertainties_in_practical_salinity_calculations. 20.08.2019.

12. Pederson A.M., Gregg M, C.1979. Development of a Small In situ Conductivity Instrument // IEEE J Ocean Engineering. V. OE-04. N 3. pp. 69–75.

13. Perkin R.G., and E. L. Lewis, 1980: The practical salinity scale1978: Fitting the data // IEEE J. Oceanic Engineering. V. OE5, no.1. рр. 9–16.

14. Saunders, P. M., Mahrt, K.-H., and Williams, R. T. 1991. Standard and Laboratory Calibration, WHP Operations and Methods, Juli, рр. 0–11. https://cchdo.github.io/hdoassets/documentation/manuals/pdf/91_1/saunders.pdf. 26.09.2019.