Dual-frequency Acoustic Seabed Classification on the Scotian Shelf, Canada

Acoustic seabed classification is typically done using single acoustic frequencies, although it is known that different frequencies can potentially provide additional information on the seabed. This thesis explores the potential of using two acoustic frequencies, 38 kHz and 120 kHz, from a single beam echo sounder for acoustic seabed classification on the Scotian Shelf, Canada. The main goals were to assess the characteristics of near-nadir acoustic backscatter as a function of seabed substrate properties and acoustic frequency, analyze differences in frequency response at different spatial scales, and to compare single frequency and dual-frequency classifications of seabed substrate types. Univariate and multivariate statistical methods were used to determine the statistical characteristics of single and dual-frequency near-nadir acoustic backscatter and to identify frequency differences. Both supervised and unsupervised classification techniques were used to classify the data. Results revealed trends in dual-frequency near-nadir backscatter such as higher frequencies and larger sediments generally produce higher backscatter and more heterogeneous and rough seabeds produce variable backscatter. It was found that differences in frequency responses of backscatter occurred at scales of hundreds of meters. Finally, it was concluded that dual-frequency classification improved upon single frequency classification at near-nadir incidence angles.