Laboratory measurements of sound scattering from a buried sphere above and below the critical angle (L)

Abstract

Laboratory measurements of low frequency (1–10 kHz) evanescent wave field scattering from a sphere buried in water-saturated sand was examined. A 60 cm stainless steel sphere was buried just below a sand–water interface and the acoustic backscattering cross section was measured for above and below critical angle geometries. The below critical angle insonification results clearly show significant levels of backscatter from the buried sphere due to evanescent wave insonification at the lower end of the spectrum (1–3.5 kHz). These measurements compare favorably with first principle estimates of the backscattered target strength and with a T-matrix-based numerical model.