Environmental variations, such as changes in sound speed profile caused by internal waves, lead to fluctuations in transmission loss from an acoustic source at specific ranges and depths. Data collected by NUWC Division Keyport and APL-UW in 2020 using a mid-frequency, vertical aperture receiving array in relatively shallow water (∼180 m depth) allowed for the measurement of both environmental and resultant acoustic fluctuations. The statistical analysis of the variability in 3.5 kHz source transmissions over a 5.5-km range is presented using histograms of the signal vertical angle of arrival and transmission loss over time. Additionally, factors like freshwater runoff, tidal actions, and wind significantly influence the observed 3.5 kHz source arrivals (including direct path and surface bounce) on the vertical array.
Grant C. Eastland (Tue,) studied this question.