A performance study of acoustic interference structure applications on source depth estimation in deep water

A recent publication by Duan et al. [J. Acoust. Soc. Am. 142(3), EL245-EL250 (2017)] analyzed the interference pattern observed in the plot of acoustic intensity versus source-receiver range and frequency in deep water. This paper extends this work by applying an equivalent acoustic intensity surface versus the vertical angle of arrivals and frequency to depth estimation of broadband sources. A matched-interference-structure (MIS) method that processes the whole acoustic intensity surface is proposed and formulated as a filtration of the surface where the binominal filter weights ±1 for each surface grid point and presumed source depth are based on model-based interference structures. For comparison, the conventional method of matching multipath delays is reformulated and applied to process the surface. Because the numerical prediction of interference structures can be costly, analytical expressions are derived to improve the efficiency. Monte Carlo simulations are carried out to compare the performance and experimental data of broadband random sequences and pulse sources are used to illustrate the methods. The MIS method has a higher resolution and can work under a lower signal-to-noise ratio in the case of weak source depth fluctuation but is not as robust to the large source depth fluctuation as the other method.