Shannon Steele

Combined Honours in Earth Sciences and Oceanography

B.Sc. (Honours) Thesis

MODELLING MID-FREQUENCY SCATTERING AND REVERBERATION IN THE NORTHERN GULF OF MEXICO

(PDF - 7.9 Mb)

Accurate sonar target detection requires the prediction of reverberation, which masks the target signal. Scattering and reverberation at mid-frequencies(1-10kHz) has not been as well studied as high-frequencies (above 10kHz). Thus, in this study, the validity of a high-frequency reverberation model for mid-frequencies was tested using environmental data collected during Target and Reverberation Experiment 2013 (TREX13). During the TREX13 sea trial it was observed that reverberation varied counterintuitively: with peak reverberation occurring within the troughs of the sand dunes. In order to investigate this spatial variation in reverberation environmental data collected during TREX13 was utilized in a high-frequency seafloor scattering model known as the composite roughness approximation (CRA). The results from this model were incorporated into a high-frequency reverberation model and compared to measured reverberation. Sub-bottom profiler data was used to visualize and quantify the spatial variation and physical mechanisms of scattering. Results from both the CRA and sub-bottom profiler indicate that volume scattering is the dominant scattering mechanism at mid-frequencies in the northern Gulf of Mexico. The peak scattering appears to be caused by the concentration of sub-surface volume scatterers in the transition zones between the peaks and troughs of the sand dunes. This study found the CRA empirical estimates of volume scattering underestimated the measured volume scattering, suggesting the CRA model should only be utilized for mid-frequency scattering if the volume scattering parameter can be calculated. This correction to the CRA model accurately predicts bottom reverberation, however the total reverberation model deviates significantly from the measured data, indicating that the other sub-models utilized in the reverberation model require validation for mid-frequencies.

Keywords: 
Pages: 65
Supervisor: David Barclay (Oceanography) and Sean Pecknold (DRDC)