Comparison of data and model predictions for Heard Island acoustic transmissions

Propagation paths and signal characteristics from the Heard Island Feasibility Test are modeled using a combination of adiabatic mode theory, coupled mode theory, and parabolic equation (PE) methods. Adiabatic mode theory predicts the horizontal propagation paths (including small grazing angle reflections from bathymetry), group travel times, and estimates of signal loss due to bottom interaction. The PE calculations are performed primarily to illustrate modal coupling near sharp oceanic fronts and bathymetry intruding into the sound channel. They are carried out in depth and range along selected horizontal ray paths. For the Heard Island to Christmas Island path, we carry out a time domain pulse transmission using coupled mode equations. The result gives a pulse envelope in approximate agreement with observations.