Quantitative evaluation for variability characteristics of reflected sound waves from sea surface

Abstract

Many kinds of hydroacoustic devices are used in the field of ocean development of resources and observations. In evaluating the effect of sound propagation in water, it is important to evaluate the characteristics of sound reflection on sea surface. Amplitude and phase of reflected sound waves often fluctuates because of the changing sea surface with waves. In this paper, we evaluated the amplitude and phase variability characteristics of reflected sound waves on sea surface by acoustic simulation with the finite difference time domain method and water tank test. It is revealed that the energy ratio γ for amplitude variability is uniquely determined by Rayleigh roughness parameter when the sea surface is sufficiently random or the number of surface waves included in the irradiation range of sound waves is large. In addition, the standard deviation of phase for the phase variability is determined by regardless of that is, sea surface spectrum.

Investigation of the Variability Characteristics of Sound Waves Reflected on the Sea Surface Considering Surface Wavelength

“…The authors have examined the impact of the wave height and wavelength of the sea surface waves on variability characteristics through a model experiment in a wave-making tank and simulation with a finite-difference-time-domain (FDTD) method. 14,15) In this paper, we report on the mechanism of the effect of wave height and wavelength of the wave on the sea surface on variability characteristics of the sea surface reflected wave.…”

“…Previous studies also showed that the amplitude variability characteristics of the sea surface reflected wave can be described with σ z . [12][13][14] In this study, σ z was calculated using the water level immediately above the sound source for the sea surface in the simulation. Equation (6) shows the relationship between sea surface wavelength Λ and period T observed under the deep-water wave conditions, in which gravitational waves are dominant.…”

“…Previous studies have shown that there is a good correlation between the amplitude variability characteristics of sea surface reflected wave and the Rayleigh roughness parameter, 26) which is the roughness of sea surface. [12][13][14] The Rayleigh roughness parameter is expressed with 2 kσ z cos φ (k: wave number, φ: incident angle of the sound wave) as shown in Fig. 7.…”

Experimental demonstration on long-range time-reversal multiple-input/multiple-output underwater acoustic communication over tens of kbps in 12.5 km range

“…The first arrival group recorded up to the delay duration about 50 ms are considered to be multiple arrivals of reflected at bottom and refracted at shallow layer. The second and third arrival groups are sparse arrivals including surface [25][26][27][28] therefore it should be noted that there might be some relation to the wind speed fluctuations. Figure 9 shows a Rx channel mean frequency response of measured CIR and transmission voltage response (TVR) of the transducer used for the element of Tx.…”

Recent techniques on sound field simulation

“…Various numerical methods such as the finite-difference method, 1) the finite element method, 2) and the boundary element method 3) have been proposed for the sound field analysis. In recent years, the finite-difference time-domain (FDTD) method [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] has been widely used because of its simple algorithm and easy programming. This is a tutorial paper focusing on the FDTD method.…”