Nine-term equation for sound speed in the oceans

A simple yet accurate nine-term, eight-variable equation for sound speed in the oceans, suitable for programmable pocket calculators, is presented. Ranges of validity encompass: temperature −2° to 30° C, salinity 30° to 40°/°°, and depth 0 to 8000 m. Good quality oceanographic data at 15 worldwide stations, including two in the Mediterranean, were utilized for the computations. The Del Grosso and Mader J. Acoust. Soc. Am. 52, 961–974 (1972) sound-speed equation was employed as ’’truth’’ after comparisons among Wilson J. Acoust. Soc. Am. 32, 641–644. 1357 (1960) and others. A precise method of computing pressure is detailed. Practical differences in critical depth, excess depth, conjugate depth, deep sound-speed gradients, and echo-sounder corrections are shown to be small between computations based on Wilson or Del Grosso and Mader sound-speed equations.