The dependency of the magnitude of acoustic variability in the open ocean on parameters characterizing the medium and the acoustic system itself is examined on the basis of in‐situ measurements of transmission loss and concurrent environmental and meteorological conditions. The spectrum of conditions considered consists of frequencies of 2.2 kHz, 8 kHz, 16 kHz, and 25 kHz; transmission ranges up to 24 000 yds; source and receiver depths up to 500 ft; and the environmental conditions experiences in the North Atlantic Ocean. Acoustic variability is observed to depend upon frequency in a nonmonotonic manner; to increase with time between transmissions for values of Δt up to approximately 40 min; to be a maximum at a range of approximately 4000 yds; to decrease significantly at sea state 4 and above; to depend upon the path that the energy travels; and to be higher when encountering the thermocline than when transmission is entirely in the mixed layer.

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