Speed of sound

Speed of sound in seawater is a function of salinity, temperature, and pressure. The units of measurement are m/s (metres per second).

It is not always possible to measure the speed of sound in seawater directly. However, we can derive it from measurable properties: electrical conductivity, temperature, and pressure, obtained by your RBR instrument, such as RBRconcerto³ C.T.D. RBR CT instruments (such as RBRduo³ C.T, without a pressure sensor) will calculate the speed of sound if you enter depth in the table under the Parameters tab in Ruskin. See Ruskin User Guide: Standard Instruments³.

We derive salinity first, via the PSS78 method, and then use it in the algorithm, often referred to as the UNESCO equation. See Speed of sound in seawater as a function of salinity, temperature, and pressure by G.S.K. Wong and S. Zhu for more details.

In the oceans, the speed of sound varies between 1450 and 1570m/s. It increases about 1.3m/s per each 1PSU increase in salinity, 4.5m/s per each 1°C increase in temperature, and 1.7m/s per each 1dbar increase in pressure.