Abstract:
Shallow-water mine counter measurement is difficult due to high noise levels, a complex environment, and a low-frequency cutoff for waterborne modes. However, interface waves may be used as a probe since they have no cutoff frequency. Further advantages are that interface waves have less geometrical spreading than volume waves. A high-order 3-D elastic finite-difference scheme is used to solve the problem. With a sloping seafloor and the mine included, there are no simplifying symmetries. At low frequencies, approximately 30 Hz, a mine can be represented as a point diffractor. The mine is assumed to be buried just below the seabottom interface. The detectors are geophones on the seafloor and on the beach. The potential for interface waves (Scholte and Rayleigh waves) excited by a source and scattered by a mine to be detected at the geophone locations has been investigated. Several experimental configurations are analyzed with the source located in the water, on the seafloor, and on the beach. Calculations have been performed with variations in the physical properties of the mine. A force source on the seafloor or beach gives results which are easier to interpret than for a volume source in the water layer. For realistic physical properties of a plastic mine the backscattered signal was found to be -60 dB compared to the outgoing signal.