Reciprocal transmission tomography experiments in the Florida Straits have yielded a month-long time history of reciprocal pulse responses over three ranges approximately 22 km in length and 250 m in depth. A transmitted pulse of 8.75 ms in duration is spread out approximately 150 ms. The detectable time spread, or pulse width, is observed to vary by as much as 120 ms over time scales on the order of days. In a previous paper a strong correlation was reported between the sound-speed gradient at mid-depth and the total pulse width. A plausible explanation that changes in the sound- speed profile shape was causing the ray arrivals to focus and defocus in time was set forth as a hypothesis for this study, to be examined with range- dependent ray and PE models. The models predict a different and unexpected relation. Variations in the sound-speed profile from the average profile shape to a more convex profile increase the bottom grazing angle to the early arrivals. This results in an attenuation of the early arriving portion of the pulse below ambient noise and therefore an apparent narrowing of the pulse. Likewise, changes in the sound-speed profile from the average profile shape to a linear profile, produce smaller bottom grazing angles for the fastest arrivals, less loss, and an overall wider appearing pulse.
ASJC Scopus subject areas
- Arts and Humanities (miscellaneous)
- Acoustics and Ultrasonics