Equation of Mackenzie

c(D,S,T) =   1448.96 + 4.591T - 5.304 x 10-2T2 + 2.374 x 10-4T3 + 1.340 (S-35) + 1.630 x 10-2D + 1.675 x 10-7D2 - 1.025 x 10-2T(S - 35) - 7.139 x 10-13TD3
 
  T = temperature in degrees Celsius
S = salinity in parts per thousand
D = depth in metres

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Range of validity: temperature 2 to 30 C, salinity 25 to 40 parts per thousand, depth 0 to 8000 m

The above equation for the speed of sound in sea-water as a function of temperature, salinity and depth is given by Mackenzie equation (1981).

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Reference

    K.V. Mackenzie, Nine-term equation for the sound speed in the oceans (1981) J. Acoust. Soc. Am. 70(3), pp 807-812