On the Feasibility of a Matched-Field Inversion in a Three-Dimensional Oceanic Environment Ignoring Out-of-Plane Propagation

Inverse problems in ocean acoustics are based on 2-D modeling of sound propagation, hence ignoring the effects of horizontal refraction, referred to as 3-D propagation effects. However, the acoustic propagation in shallow-water environments, such as the continental shelf, may be affected by 3-D effects requiring 3-D modeling to be accounted for. The aim of this work is to investigate the importance of the 3-D effects with respect to the performance and reliability of typical 2-D-model-based inversion procedures of ocean acoustics. The study is carried out on a well-established synthetic test case which exhibits well-known 3-D effects. A matched-field inversion procedure is implemented based on the exhaustive search over the parameter space. The feasibility and the limits of inverting low-frequency noisy 3-D synthetic data for some parameters describing the test case by matching replica from 2-D computations are explored. Both synthetic data and replica are generated using a parabolic-equation-based code. This approach highlights the relevance of using 2-D propagation models when inversions are performed at relatively short ranges from the source. On the other hand, important mismatch occurs when inverting at farther ranges, demonstrating that the use of fully 3-D forward models is required.