New Equations for Sea Water Density Calculation Based on Measurements of the Sound Speed

Density is one of the most important properties of seawater and is used in various marine research and technology. Traditionally, in the practice of oceanographic research, it is customary to consider density as a dependent  parameter, which is a function of several other parameters taken  as independent.  Usually the following three parameters are used as the independent  parameters: temperature, hydrostatic  pressure  and  salinity.  The  issues  of  temperature  and  hydrostatic  pressure  measuring  in  situ  are  technologically  well developed,  while in the salinity measuring there are still unsolved problems. This is due to the fact that salinity is such a property that it is simply impossible to determine  directly in situ. To  eliminate  the problems associated  with measurements  of salinity, the authors developed  the special new kind  equation.  That  equation  of the new kind  express the density  of sea water through independent  and in situ measured  parameters:  temperature, hydrostatic  pressure and  sound  speed.  The  novelty  of this approach  is that  using of the sound speed as the independent  parameter makes  it possible to exclude measurements  of salinity. The authors developed two such new equations  for the different cases of using. The  first new equation  is intended  for use in technical  applications and reproduces the sea water density in a wide range of the aquatic environment  parameters with a root mean square deviation  of 0.062  kg/m³. The  second more precise new equation  is intended  for scientific applications  and  reproduces the sea water density  in a narrower oceanographic range of parameters with a root mean  square deviation  of 0.0018  kg/m³.

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