Doppler Spectra of Bistatic Reverberation from the Sea Surface

摘要

The Doppler spectra of sea surface reverberation were investigated in a shallow water environment. A parametric array projected a narrow beam of acoustic energy at the surface and insonified on the surface a well-defined scattering area of limited extent. The surface generated reverberation was received on eight closely spaced hydrophones of a vertical array. The power spectral densities of the instantaneous reverberation--the Doppler spectra--were of primary interest in the analyses of the reverberation data. Doppler spectra were measured as a function of the transmitted parametric difference frequency, the angle of incidence of the array to the sea surface, and the angle of scatter of the reverberation to the receiving hydrophones. In concert with the reverberation experiment, the directional spectrum of the sea surface waves was measured with an acoustic wave height sensing system. A line array of acoustic wave height sensors simultaneously measured the time varying wave height at five discrete points on the sea surface. It is concluded that the surface reverberation Doppler spectra and the sea surface directional spectrum represent a unique data collection that can be used for theoretical reverberation model development and subsequent model verification. Furthermore, the Doppler spectra are applicable to the system design and performance prediction of surface reverberation-limited sonar systems operating in low sea states and at similar sonar frequencies.