The influence of mode coupling on waveguide invariant

Abstract

The waveguide invariant β is typically discussed in terms of either a range-independent environment or a range-dependent environment under the adiabatic approximation, with few studies considering the effects of mode coupling. In this work, how internal solitary waves (ISWs) affect the waveguide invariant is investigated, and it is shown that mode-coupling effects introduce many additional components in the acoustic interference intensity. It is found that the striation slope and value of β for these additional components are determined not only by the acoustic modal dispersion, but are also dependent on the position where the mode coupling occurs. This can lead to a very complicated acoustic interference pattern and result in multiple peaks in the distribution of β. The sensitivity of β to the parameters of ISWs, such as amplitude, horizontal scale, and position, is analyzed. It is found that although all parameters can affect the energy of the peaks, only the position of the internal wave has an obvious impact on the peak values. This indicates that the peak values of β can be utilized for monitoring the position of the internal wave.

Training a U-Net based on a random mode-coupling matrix model to recover acoustic interference striations

“…is the mode-coupling matrix which is caused by the horizontal inhomogeneity, such as NLIW, between 1 r and 2 r [16,17]. Mode-coupling effects introduce many additional components in AISs [13] which results in the distortion of the AISs. [16] and assuming that the phase change of diagonal elements in mode-coupling matrix caused by horizontal inhomogeneity can also be neglected, the random mode-coupling matrix Λ has the following form:…”

“…Generally, normal modes of adjacent numbers are more easily coupled with each other, so the coupling matrix often has a band structure [13].…”

“…AISs, which are related to waveguide-invariant β in a range-independent background ocean waveguide, have been used in source ranging [8][9][10][11]. If horizontal inhomogeneity is introduced into the background ocean waveguide, for example, range-dependent waveguides with NLIWs, AISs will be distorted due to mode coupling [12,13]. In contrast to the βdistribution of an AIS, the β distribution of a distorted AIS may have several peaks [13], which impedes waveguide-invariant related applications.…”

“…If horizontal inhomogeneity is introduced into the background ocean waveguide, for example, range-dependent waveguides with NLIWs, AISs will be distorted due to mode coupling [12,13]. In contrast to the βdistribution of an AIS, the β distribution of a distorted AIS may have several peaks [13], which impedes waveguide-invariant related applications. The purpose of AIS recovery is to eliminate the mode-coupling effect caused by the horizontal inhomogeneity and to recover the corresponding AIS from distorted AIS.…”

“…Although how an AIS becomes a distorted one by mode coupling has been studied [12,13], AIS recovery still remains unsolved in underwater acoustics. In fact, AIS recovery is to build a mapping from distorted AISs to the corresponding AISs.…”