Precision of Oceanographic Data for Sound-Speed Calculations

The precision of sound speeds calculated from oceanographic data, consisting of measurements of temperature and salinity at various depths, depends on systematic errors of the empirical formula relating sound speed to the oceanographic variables and on the errors of the measured variables. Estimates of precision, defined as twice the standard deviation, range from 0.021°–0.025°C for temperature, 0.016‰–0.072‰ for salinities determined by titration, and 7–12 m for depths to 1000 m. Systematic errors of the sound-speed formula are estimated to be about 0.5 m/sec. In a homogeneous layer of the ocean, the errors of measurement of temperature and salinity limit the precision of sound speed to 0.12 m/sec. In a stratified layer, the precision less (larger standard deviation) because of the uncertainty in the depth determination.