Using physical oceanography to improve transmission loss calculations in undersampled environments

Abstract

The vertical sound speed profile (SSP) is a critical input to any acoustic propagation model. However, even when measured SSPs are available they are frequently noisy “snapshots” of the SSP at a single moment in time and space and do not fully capture changes such as solar heating and wind-driven mixing that can significantly affect shallow water propagation on time scales of less than a day. Furthermore, SSPs measured in the field may not extend to the ocean bottom and are often based on measured profiles of temperature with an implicit assumption of constant salinity. In April–May 2013, the Target and Reverberation Experiment (TREX) was conducted in the Northeastern Gulf of Mexico near Panama City, Florida, a region strongly affected by local wind forcing, freshwater inputs, and the presence of a warm-core Gulf of Mexico Loop Current eddy ("Eddy Kraken") offshore of the experimental site. “Synthetic” SSPs were constructed for the trial area by combining knowledge of the physical oceanography and water masses in the area with the measured SSPs that were available. Transmission loss was modelled using both synthetic and measured SSPs and the results will be compared with measured transmission loss.