A study of waveguide invariant using multiple parameters

Abstract

When a surface ship of opportunity passes a single hydrophone, a distinct pattern known as the "bathtub" feature can be identified on the spectrogram of the received signal. If the ship speed and distance to the recorder are known, then useful information about the physical properties of the waveguide can be extracted using the waveguide invariant parameter (beta) describing the characteristics of the ocean acoustic waveguide. For a simple waveguide, beta can be approximated as one for all frequencies and ranges and is invariant to mode pairs. ☐ This research, through the use of the normal mode model KRAKEN, and with acoustic data gathered during the Shallow Water Canada Basin Acoustic Propagation Experiment, illustrates that beta in a complex Arctic environment does in fact change with the properties of the waveguide such as water depth, sound speed profile in the water, sediment layer structure, and the seafloor physical properties. The value of waveguide invariant also changes with the frequency and mode pair selected.