Impacts of range-dependent bottom type on mid-frequency propagation

Abstract

The Target and Reverberation Experiment in 2013 (TREX13) focused on mid-frequency propagation and reverberation in shallow water off the coast of Panama City Beach, FL. The seafloor at the site primarily consisted of long-wavelength (150–200 m), small-amplitude (∼1 m) sand ridges with narrow (20–30 m wide) regions of mud in the swales. Backscatter measurements using a multibeam sonar indicated that roughly 10%–20% of the seafloor was covered in mud. During the experiment, a source transmitting tones from 1.5 to 4.0 kHz was towed past two stationary vertical line arrays to measure the transmission loss (TL) along the track. The measured TL was found to be midway between the predictions for pure sand and puremud sediments, despite the limited amount of mud at the site. Range-dependent propagation models which incorporate this variation in sediment type, indicate that the mud regions act as sinks of acoustic energy producing a significant increase in loss. Also, the spatial distribution is such that the mud regions cannot be discerned in the TL range-dependence. The implications of this range-dependence on both inversion and reverberation will be discussed. [Work supported by the U.S. Office of Naval Research.]