A Normal Mode Reverberation and Target Echo Model to Interpret Towed Array Data in the Target and Reverberation Experiments

Reverberation measurements obtained with towed arrays are a valuable tool to extract information about the ocean environment. By superimposing a polar plot of reverberation beam time series on bathymetry maps, bottom features (often uncharted) can be located. As part of Rapid Environmental Assessment exercises, Preston and Ellis used directional reverberation measurements to extract environmental information using model-data comparisons. This early work used range-independent (flat bottom) ray-based models for the model-data comparisons, while current work includes range-dependent models based on adiabatic normal modes. Here, we discuss a range-dependent shallow-water reverberation model using adiabatic normal modes that has been developed to handle bottom scattering and clutter echoes in a range-dependent environment. Beam time series similar to those measured on a horizontal line array can be produced. Comparisons can then directly be made with data, features identified, and estimates of the scattering obtained. Of particular interest will be data obtained on the triplet line array during the 2013 Target and Reverberation EXperiments in the Gulf of Mexico off Panama City, FL, USA, where interesting effects in sea bottom sand dunes were observed. Particular attention has been paid to calibration to get estimates of scattering strengths. In addition to the reverberation, a preliminary investigation of the target echo is presented.