On equations for the speed of sound in seawater

TLDR

Sound‑speed fields computed using the Del Grosso equation predict acoustic arrival patterns that agree significantly better with long‑range measurements than those computed using the Chen and Millero equation. Long‑range acoustic transmissions with extensive environmental measurements and accurate mooring positions were used to test sound‑speed equations, and predicted ray travel times were calculated from objectively mapped sound‑speed fields derived from CTD and XBT data. Del Grosso’s equation predicts acoustic arrival patterns more accurately than Chen and Millero’s, with a negligible correction of +0.05 ± 0.05 m s⁻¹ at 4000 m depth. References include Del Grosso (1974) and Chen & Millero (1977) for sound‑speed equations.

Abstract

Long-range acoustic transmissions made in conjunction with extensive environmental measurements and accurate mooring position determinations have been used to test the accuracy of equations used to calculate sound speed from pressure, temperature, and salinity. The sound-speed fields computed using the Del Grosso equation [V. A. Del Grosso, J. Acoust. Soc. Am. 56, 1084–1091 (1974)] give predictions of acoustic arrival patterns which agree significantly better with the long-range measurements than those computed using the Chen and Millero equation [C. Chen and F. J. Millero, J. Acoust. Soc. Am. 62, 1129–1135 (1977)]. The predicted ray travel times and travel time error have been calculated using objectively mapped sound-speed fields computed from conductivity, temperature, depth (CTD) and expendable bathythermograph (XBT) data. Using the measured and predicted ray travel times, a negligible correction to Del Grosso’s equation of +0.05±0.05 m/s at 4000-m depth is calculated.