Precision In-Situ Sound-Speed Measurements Aboard DEEPSTAR-4000 and Comparisons with Extant Equations

Abstract

Accurate measurements of in-situ sound speed, temperature, salinity, and pressure have been achieved during numerous replicating dives aboard Westinghouse DEEPSTAR-4000 to depths of 1200 m. Manned deep submergence vehicles offer optimum methods for observing the actual ocean environment. Advantages of submersibles include: capabilities of mounting multiple equipments with short cables, visually monitoring instruments during data acquisition, and controlling proximity to the seafloor—significant improvements over suspending sensors with miles of cables from rolling, pitching surface craft. Instrument packages have consisted of three precision velocimeters (two NUS TR-4's and one TR-5), two Dymec temperature sensors, one Bissett-Berman salinometer, one or two Vibrotrons, and four Fjarlie bottles with four reversing thermometers each. Accuracy is enhanced by meticulous calibrations before and after dive series, delicate handling of all equipment, intercomparison of several instruments, consistently careful measurements, and correct assessments of thermal lags and pressure effects. Results are compared with existing equations for sound speed versus temperature, salinity, and pressure.