Acoustic mode coupling effect predicted by new criterion of adiabatic invariance resulting
from both internal wave and shelf break
Linus Y.S. Chiu1, Andrea Y.Y. Chang1, and Chi-Fang Chen1
Department of Engineering Science and Ocean Engineering, Nation Taiwan University, No. 1, Sec.
4, Roosevelt Road, Taipei, 10617 Taiwan, Republic of China, E-mail: f91525002@ntu.edu.tw
1
Abstract
Acoustic inversion is the approach of using acoustic data to determine the model input parameters
used in computational models. Robustness of acoustic forward propagation model therefore
contributes to accuracy of acoustic inversion. Propagation through a medium having a
range-dependent sound speed profile can result in energy transferring between acoustic modes. The
absence of mode coupling between two particular modes is termed adiabatic invariance. We
proposed a new criterion of adiabatic invariance to determine the environmental regimes in which
adiabatic invariance or mode coupling will hold true for mode pairs, and to examine the acoustic
coupling effect resulting from both slope-bathymetry (shelf break) and internal wave. Analytic
solution is proposed in this paper, and is manifested by numerical experiments and measured data.
Different parameters such as wave-length, horizontal scale of internal wave, and sloping rates of
bathymetry affecting the coupling strength of acoustic mode pairs are also illustrated. The results
showing the higher order modes appear as the internal wave is propagating via shelf break, can be
manifested and predicted by the new criterion of adiabatic invariance. This new criterion can
potentially form the forward modeling of acoustic propagation coupled from variations both of
bathymetry and water.