Fine-scale variability in temperature, salinity, and pH in the upper-ocean and the effects on acoustic transmission loss in the Western Arctic Ocean
Col, Stephen M.D.
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Acoustic propagation in the ocean is dependent on the sound speed profile, which is a function of temperature, salinity, and pressure. In the upper ocean, these variables can change quickly as a result of fronts, internal waves, diurnal heating and other mechanisms. Transmission loss (TL) is a function of geometrical spreading, absorption, and scattering. Absorption is a function of temperature, salinity, pressure, and pH. pH variability is typically omitted from TL calculations. This thesis studied the effects of variability in the vertical structure of temperature, salinity and pH on acoustic TL in the Arctic Ocean. These parameters were measured in the Beaufort Sea in March 2009 during ICEX2009 over a period of 15 days. Frequencies considered in this study were 100Hz, 1kHz, and 10kHz. This range of frequencies brackets the boric acid relaxation frequency and is of interest to the U.S. Navy for anti-submarine warfare. Expected absorption losses were estimated by integrating the loss over individual ray paths. Calculations were performed with constant pH as well as by using the measured depth dependent pH. The resulting difference in total absorption losses computed with constant versus variable pH was less than 2dB over a 50km distance. The error in transmission loss calculations due to ignoring pH variability is expected to be very small compared to the uncertainties due to ice scatterabsorption. Therefore, routine measurements of the depth dependent pH levels are not recommended for the purpose of transmission loss calculations under Arctic ice cover.
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