Seawater Salinity Estimating Module Based on the Sound Velocity Measurements

А. P. Tolstosheev✉, E. G. Lunev, S. V. Motyzhev, V. Z. Dykman

Marine Hydrophysical Institute of RAS, Sevastopol, Russian Federation

✉ e-mail: tolstosheev@marlin-yug.com

Abstract

Purpose. Reliability of knowledge about the ocean dynamics and climate variability is largely limited for lack of systematic in situ observations of the sea surface layer salinity, which is one of the basic hydrological parameters determining circulation and stratification of the water masses. The study is aimed at developing an autonomous device for long-term monitoring of salinity in the seawater upper layer.

Methods and Results. One of the most effective tools for in situ observations of the ocean upper layer is the global network of surface drifting buoys – drifters. At present, the network consists of more than 1500 buoys, but only a few of them provide sea surface salinity observations within the framework of a limited number of pilot experiments. In the drifters, salinity is calculated by the traditional method using the results of the electrical conductivity and temperature measurements. There are a few problems related both to the principle of determining salinity by this method and to providing long-term stable running of conductivity sensors under the conditions of pollution and biological fouling. A drifter equipped with the module for the sound velocity and temperature measurements used for calculating salinity by an alternative method just aboard the drifter, was developed in Marine Hydrophysical Institute, Russian Academy of Sciences. The sound velocity and temperature module includes a specially designed time-of-flight sound velocity sensor with the fixed base and a quartz temperature sensor. In course of two years, numerous laboratory and in situ tests of several prototypes of the sound velocity and temperature module were performed. The laboratory tests showed that the repeatability limits for the results of the sound velocity measurements in the distilled water were ±0.02 m/s. According to the data of the long-term in situ tests performed at intensive biological fouling, the error of salinity estimation resulted from of the sound velocity and temperature measurements were within ±0.05 ‰. This result permits to expect that the sound velocity and temperature module parameters will remain stable in real conditions of long-term autonomous operation.

Conclusions. The obtained results make it possible to recommend application of the drifters equipped with the modules for the sound velocity and temperature measurements as an effective tool for regular operational monitoring of the salinity field of the upper sea layer.

Keywords

drifting buoy, seawater, sound velocity, temperature, salinity

Acknowledgements

The authors are grateful to the reviewers for their valuable comments and methodological assistance. The study was carried out within the framework of the state task on theme "Development of methods and means of operational oceanology for studying the variability of the Black Sea fields" ("Black Sea" code) of the Program of fundamental scientific research of the Presidium of the Russian Academy of Sciences No. 20 "New challenges of the Earth's climate system" for 2019 at the financial and technical support of “Marlin-Yug” Ltd.

Original russian text

Original Russian Text © The Authors, 2021, published in MORSKOY GIDROFIZICHESKIY ZHURNAL, Vol. 37, Iss. 1, pp. 132-142 (2021)

For citation

Tolstosheev, A.P., Lunev, E.G., Motyzhev, S.V. and Dykman, V.Z., 2021. Seawater Salinity Estimating Module Based on the Sound Velocity Measurements. Physical Oceanography, [e-journal] 28(1), pp. 122-131. doi:10.22449/1573-160X-2021-1-122-131

DOI

10.22449/1573-160X-2021-1-122-131

References

  1. Motyzhev, S.V., Lunev, E.G. and Tolstosheev, A.P., 2016. The Experience of Barometric Drifter Application for Investigating the World Ocean Arctic Region. Physical Oceanography, (4), pp. 47-56. doi:10.22449/1573-160X-2016-4-47-56
  2. Motyzhev, S.V., Lunev, E.G. and Tolstosheev A.P., 2017. The Experience of Using Autonomous Drifters for Studying the Ice Fields and the Ocean Upper Layer in the Arctic. Physical Oceanography, (2), pp. 51-64. doi:10.22449/1573-160X-2017-2-51-64
  3. Reverdin, G., Morisset, S., Boutin, J., Martin, N., Sena-Martins, M., Gaillard, F., Blouch, P., Rolland, J., Font, J., Salvador, J., Fernandez, P. and Stammer, D., 2014. Validation of Salinity Data from Surface Drifters. Journal of Atmospheric and Oceanic Technology, 31(4), pp. 967-983. doi:10.1175/JTECH-D-13-00158.1
  4. Hormann, V., Centurioni, L. and Reverdin, G., 2015. Evaluation of Drifter Salinities in the Subtropical North Atlantic. Journal of Atmospheric and Oceanic Technology, 32(1), pp. 185-192. doi:10.1175/JTECH-D-14-00179.1
  5. Centurioni, L.R., Hormann, V., Chao, Y., Reverdin, G., Font, J. and Lee, D.-K., 2015. Sea Surface Salinity Observations with Lagrangian Drifters in the Tropical North Atlantic during SPURS: Circulation, Fluxes, and Comparisons with Remotely Sensed Salinity from Aquarius. Oceanography, 28(1), pp. 96-105. doi:10.5670/oceanog.2015.08
  6. Dong, S., Volkov, D., Goni, G., Lumpkin, R. and Foltz, G. R., 2017. Near-Surface Salinity and Temperature Structure Observed with Dual-Sensor Drifters in the Subtropical South Pacific. Journal of Geophysical Research: Oceans, 122(7), pp. 5952-5969. doi:10.1002/2017JC012894
  7. WMO, 2011. Sea Surface Salinity Quality Control Processes for Potential Use on Data Buoy Observations. DBCP Technical Document No. 42. [online] Available at: https://library.wmo.int/doc_num.php?explnum_id=7078 [Accessed: 24 May 2020].
  8. Allen, J.T., Keen, P.W., Gardiner, J., Quartley, M. and Quartley, C., 2017. A New Salinity Equation for Sound Speed Instruments. Limnology and Oceanography: Methods, 15(9), pp. 810-820. doi:10.1002/lom3.10203
  9. Von Rohden, C., Fehres, F. and Rudtsch, S., 2015. Capability of Pure Water Calibrated Time-of-Flight Sensors for the Determination of Speed of Sound in Seawater. The Journal of the Acoustical Society of America, 138(2), pp. 651-662. doi:10.1121/1.4926380
  10. Babiy, V.I. and Tolstosheev, A.P., 1999. [Working Instruments for Measuring the Velocity of Sound in the Marine Environment]. Sevastopol: MHI, 36 p. (in Russian).
  11. Meleshko, E.A., 1978. [The Integrated Circuit in the Nanosecond Nuclear Electronics]. Moscow: Atomizdat, 216 p. (in Russian).
  12. Babii, V.I., 2017. On the Metrology of the Speed of Sound in Liquids. Acoustical Physics, 63(3), pp. 275-287. https://doi.org/10.1134/S1063771017030034
  13. Del Grosso, V.A. and Mader, C.W., 1972. Speed of Sound in Pure Water. The Journal of the Acoustical Society of America, 52(5B), pp. 1442-1446. doi:10.1121/1.1913258
  14. Delauney, L., Compère, C. and Lehaitre M., 2010. Biofouling Protection for Marine Environmental Sensors. Ocean Science, 6(2), pp. 503-511. doi:10.5194/os-6-503-2010

Download the article (PDF)

We use Yandex Metrics. Read more.

Мы используем Яндекс Метрику. Подробнее.