底質物理量と音響パラメータとの対応性

抄録

On this paper, we describe the result in a basic study for a technical developing classification of coastal bottom material by using of acoustic reflection method. As the item of classification of bottom material, we selected, especially, such physical properties as grain size distribution and volume concentration (porosity) of particles in soft-mudsediment. Newly physical parameter CPC (cumulative weight percentage of particle volume concentration) is defined.
The other hand, we have derived a new conception of acoustic propagation, sound velocity and attenuation, for a model of N-phase suspension. In the conception, the volume ratio of N-phase particles classified by grain size in modefied suspension is particularly introduced.
The applicability of the conception for the soft-mud sediment was verified through both numerical simulations and laboratory experiments measuring physical properties, sound speed and attenuation at several frequencies.
A center frequency f of sound speed dispersion has a good response with the mediam grain size φ_m (φ_m=-log₂ 2 a_m; a_m is radius of particle in milli-meter) in the CPC curve. Then, the regressive formulation is
φ_m=1.62 F+3.99±0.244
where F≡log₁₀ f; f in kHz.
A maximum V_m of sound velocity at higher frequency range, eg. several hunderd kilo-hertz to several hundred mega-hertz, etc., is corresponding to the maximum of CPC curve at each volume concentration C_p. The theoretical formulation is
C_p=CPC={1.125 (V_m-1)}^1/2
where V_m=|V_s/V_l|_max.
By using these formulas, φ_m and C_p can be predicted from measured F and V_m.