Stability and a fast calculation method of travel speed of pulse peak in convergence zone

A long-range sound propagation experiment was conducted in the West Pacific Ocean in summer 2013. The signals received by a towed array indicate that the travel speed of pulse peak (TSPP) in the convergence zones is stable. Therefore, an equivalent sound speed can be used at all ranges in the convergence zones. A fast calculation method based on the beam-displacement ray-mode (BDRM) theory and convergence zone theory is proposed to calculate this equivalent sound speed. The computation speed of this proposed method is over 1000 times faster than that of the conventional calculation method based on the normal mode theory, with the computation error less than 0.4% compared with the experimental result. Also, the effect of frequency and sound speed profile on the TSPP is studied with the conventional and fast calculation methods, showing that the TSPP is almost independent of the frequency and sound speed profile in the ocean surface layer.