Possibilities of measuring the local density of seawater in probe instruments

V.A. Gaisky,  P.V. Gaisky

Institute of Natural and Technical Systems, Russian Federation, Sevastopol, Lenin St., 28

Email: gaysky@inbox.ru

DOI: 10.33075/2220-5861-2021-1-61-67

UDC 621.384

Abstract:

   In modern expeditionary research carried out on research vessels, the local density of seawater is not measured, but calculated using the TEOS-10 thermodynamic equation of state based on cumulative measurements of pressure, temperature and electrical conductivity or speed of sound. The equation of state with satisfactory accuracy is valid only for oceanological waters, and is used with corrections for the waters of the marginal and inland seas. These corrections are permanently refined and will be refined in the future. It is desirable to have direct measurements of the local density of any waters directly in the environment with sufficient accuracy, which is now 4·10-6. Laboratory measurements made by various methods and with different devices, not always automated, give accuracy ~ . Attempts to automate these measurements and introduce them into sounding devices have been made several times. Experimental samples of vibration, refractometric and hydrostatic devices have been created and tested, none of which have been introduced into the practice of expeditionary work for various reasons. However, scientific and technological progress makes possible technical solutions previously difficult to implement. This also applies to modifications of the hydrostatic method for measuring the local density, which have recently attracted the interest of developers.

   The paper analyzes the possibilities of implementing the hydrostatic method using multi-element resistor distributed pressure and temperature sensors, resistance profilers of these sensors and determining the spatial pressure drop on a given base by measuring and subtracting sensor resistances, taking into account temperature correction. The use of three such sensors, mounted on three rods, oriented downward along the axes of a rectangular coordinate system, provides the possibility of measuring the local density with an arbitrary orientation of the probe relative to the vertical. The analysis shows the possibility of measuring the local density of seawater by the hydrostatic method with the required accuracy in probe instruments.

Keywords: thermodynamic equation of state, fluid density, oceanographic probe.

To quote: Gaisky, V.A., and P.V. Gaisky. “Possibilities of Measuring the Local Density of Seawater in Probe Instruments.” Monitoring Systems of Environment no. 1 (March 25, 2021): 61–67. doi:10.33075/2220-5861-2021-1-61-67.

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