Acoustic scattering from a solid aluminum cylinder in contact with a sand sediment: measurements, modeling, and interpretation.

Understanding acoustic scattering from objects placed on the interface between two media requires incorporation of scattering off the interface. Here, this class of problems is studied in the particular context of a 61 cm long, 30.5 cm diameter solid aluminum cylinder placed on a flattened sand interface. Experimental results are presented for the monostatic scattering from this cylinder for azimuthal scattering angles from 0 degrees to 90 degrees and frequencies from 1 to 30 kHz. In addition, synthetic aperture sonar (SAS) processing is carried out. Next, details seen within these experimental results are explained using insight derived from physical acoustics. Subsequently, target strength results are compared to finite-element (FE) calculations. The simplest calculation assumes that the source and receiver are at infinity and uses the FE result for the cylinder in free space along with image cylinders for approximating the target/interface interaction. Then the effect of finite geometries and inclusion of a more complete Green's function for the target/interface interaction is examined. These first two calculations use the axial symmetry of the cylinder in carrying out the analysis. Finally, the results from a three dimensional FE analysis are presented and compared to both the experiment and the axially symmetric calculations.

[1]  P. Marston.  Approximations for Leaky Wave Amplitudes in Acoustic Imaging: Applications to High Frequency Sonar , 1997 .

[2]  Raymond Lim,et al.  Evaluation of the integrals of target/seabed scattering using the method of complex images. , 2003, The Journal of the Acoustical Society of America.

[3]  Williams,et al.  Acoustic scattering by a three-dimensional elastic object near a rough surface , 2000, The Journal of the Acoustical Society of America.

[4]  Philip L Marston,et al.  Leaky helical flexural wave backscattering contributions from tilted cylindrical shells in water: observations and modeling. , 2002, The Journal of the Acoustical Society of America.

[5]  P. Marston.  Approximate meridional leaky ray amplitudes for tilted cylinders: End-backscattering enhancements and comparisons with exact theory for infinite solid cylinders , 1997 .

[6]  K. Baik,et al.  Kirchhoff Approximation for a Cylinder Breaking Through a Plane Surface and the Measured Scattering , 2008, IEEE Journal of Oceanic Engineering.

[7]  H. Schmidt,et al.  Measurements and modeling of acoustic scattering from partially and completely buried spherical shells. , 2002, The Journal of the Acoustical Society of America.

[8]  Philip L. Marston,et al.  Backscattering enhancements due to reflection of meridional leaky Rayleigh waves at the blunt truncation of a tilted solid cylinder in water: Observations and theory , 1999 .

[9]  Kevin L. Williams,et al.  Sound speed and attenuation measurements in unconsolidated glass-bead sediments saturated with viscous pore fluids , 2006 .

[10]  X. Bao.  Echoes and helical surface waves on a finite elastic cylinder excited by sound pulses in water , 1993 .

[11]  Alessandra Tesei,et al.  A computationally efficient finite element model with perfectly matched layers applied to scattering from axially symmetric objects. , 2007, The Journal of the Acoustical Society of America.

[12]  M. Gunzburger,et al.  Boundary conditions for the numerical solution of elliptic equations in exterior regions , 1982 .

[13]  Peter T. Gough,et al.  Unified framework for modern synthetic aperture imaging algorithms , 1997 .

[14]  S. K. Numrich,et al.  Scattering of acoustic waves by a finite elastic cylinder immersed in water , 1981 .

[15]  Marston,et al.  Backscattering enhancements from Rayleigh waves on the flat face of a tilted solid cylinder in water , 2000, The Journal of the Acoustical Society of America.

[16]  Alessandra Tesei,et al.  Computing the far field scattered or radiated by objects inside layered fluid media using approximate Green's functions. , 2008, The Journal of the Acoustical Society of America.