Influence of waveguide depth on bottom reverberation strength in very shallow water environments

In comparison with the shallow water environment, the very shallow water environment is more likely to generate stronger bottom reverberation, which hinders the detection for the underwater low-speed small target. To solve this problem, the mechanism and the conditions of the stronger bottom reverberation in very shallow water are analyzed in detail from the perspective of the waveguide depth. Firstly, the multipath propagation model and the bottom scattering model for underwater high-frequency acoustical energy are established. Then, the influence of the waveguide depth on the multipath structure and the bottom scattering strength are analyzed quantitively. Finally, the influence mechanism of the waveguide depth on the bottom reverberation strength is summarized. In this paper, the accumulated value of the multipath strength during a pulse width is defined to measure the bottom reverberation strength, which is the product of the number of multipath during a pulse width (NMPW) and the average strength of multipath during a pulse width (ASMPW). Taking the medium sand and the coarse silt as examples, the theoretical results are verified through numerical simulations. In terms of the coarse silt sediment, ASMPW in very shallow water is significantly lower than that in shallow water, but NMPW in very shallow water is slightly higher than that in shallow water. The ASMPW plays the dominant role in bottom reverberation strength, hence very shallow water shows no stronger bottom reverberation than shallow water. In terms of the medium sand sediment, ASMPW in very shallow water is slightly lower than that in shallow water, but NMPW in very shallow water is significantly higher than that in shallow water. The NMPW plays the dominant role in bottom reverberation strength, hence very shallow water shows stronger bottom reverberation than shallow water.