doi:
UDK: 534.2

ECHO-SIGNAL FROM A SPHERICAL SCATTERER LOCATED NEAR THE GAS-SATURATED BOTTOM

Григорьева Н. С., Сафронов К. С., Лукьянов В. Д.
Article language: русский

Annotation

The paper describes the theory and implementation issues of modeling the backscattering from a spherical target located near the gas-saturated bottom. Two cases are compared: when the sound speed in sediment is larger and smaller than the sound speed in water (rigid or soft bottom). The bottom is assumed to be a homogeneous water half-space. The transmitter/receiver is located in a homogeneous water half-space. The distance between the transmitter/receiver and the object of interest is supposed to be large compared to the acoustic wavelength. The solution is determined from the Hackman and Sammelmanns general approach. The arising scattering coefficients of the sphere were evaluated using the steepest descent method. The use of the obtained asymptotic formulae for the scattering coefficients allowed to decrease essentially the number of summands in the formula for the form function of the backscattering field. Numerical results are presented for a long-range high frequency detection of the acoustically rigid scatterer. It is shown that the form function in both cases (rigid and soft bottom) have the form of oscillating curves. Their oscillation periods decrease as the distance between the target and the transmitter/receiver increases. These oscillations are the result of the interference of a mirror reflection and waves reflected from the sphere, put on the bottom and came back to the receiver. Keywords: scattering of acoustic waves, echo-signal, spherical scatterer, single-scatter approximation, steepest descent method, gas-saturated sediment

Bibliography

1. Hackman R.H., Sammelmann G.S. Multiple-scattering analysis for a target in an oceanic waveguide, J. Acoust. Soc. Am. 1988. V. 84. № 5. P. 1813-1825.
2. Jensen F.B., Zampolli M., Tesei A. Benchmark problems for acoustic scattering from elastic objects in the free field and near the seafloor, J. Acoust. Soc. Am. 2009. V. 125. № 1. P. 89-98.
3. Grigorieva N.S., Fridman G.M. Scattering of sound by an elastic spherical shell immersed in a waveguide with a fluid bottom, Acoust. Phys. 2013. V. 59. P. 373-381.
4. Williams K.L., Kargl S.G., Thorsos E.I., Burnett D.S., Lopes J.L., Zampolli M., Marston P.L. Acoustic scattering from a solid aluminum cylinder in contact with a sand sediment: Measurements, modeling, and interpretation, J. Acoust. Soc. Am. 2010. V. 127. № 6. P. 3356-3371.
5. Zampolli M., Tesei A., Canepa G., Godin O.A. Computing the far field scattered or radiated by objects inside layered fluid media using approximate Greens functions, J. Acoust. Soc. Am. 2008. V. 123. P. 4051-4058.
6. Grigorev V.A., Lunkov A.A., Petnikov V.G. Sound attenuation in shallow water areas with a gas-filled bottom, Acoust. Phys. 2015. V. 61. P. 90-100.
7. Brekhovskikh L.M. Waves in Layered Media, 2nd edn. Academic Press, New-York, 1980.
8. Bateman H., Erdelyi A. Higher Transcendental Functions. McGraw-Hill, New York, 1953, Vol. 1.
9. Sessarego J.-P., Cristini P., Grigorieva N.S., Fridman G.M. Acoustic scattering by an elastic spherical shell near the seabed, J. Comp. Acoust. 2012. V. 20. № 3. Р. 1250006.1-19.
10. Kargl S.G., Marston P.L. Ray synthesis of Lamb wave contributions to the total scattering cross section for an elastic spherical shell, J. Acoust. Soc. Am. 1990. V. 88. № 3. Р. 1103-1113.
11. Fawcett J.A., Fox W.L.J., Maguer A. Modeling of scattering by objects on the seabed, J. Acoust. Soc. Am. 1988. V. 104. № 6. P. 3296-3304.
12. Bateman H., Erdelyi A. Higher Transcendental Functions. McGraw-Hill, New York, 1953, Vol. 2.
13. Shenderov E.L. Izlucheniye i rasseyaniye voln. Sudostroenie, Leningrad, 1989 [Radiation and dispersion of waves].
14. Fawcett J. A. Complex image approximation to the half-space acousto-elastic Greens function, J. Acoust. Soc. Am. 2000. V. 108. № 6. Р. 2791-2795.
15. Fawcett J. A., Lim R. Evaluation of the integrals of target/seabed scattering using the method of complex images, J. Acoust. Soc. Am. 2003. V. 114. № 3. Р. 1406-1415.
16. Grigorieva N.S., Kupriyanov M.S., Mikhailova D.A., Ostrovskiy D.B. Sound wave scattering by a spherical scatterer located near an ice surface, Acoust. Phys. 2016. V. 62. № 1. P. 8-21.
17. Lim R., Lopes J.L., Hackman R.H., Todoroff D.B. Scattering by objects buried in underwater sediments: Theory and experiments, J. Acoust. Soc. Am. 1993. V. 93. № 4. Pt. 1. P. 1762-1783.