Spectrum of a Signal Reflected from a Time-Varying Random Surface
Abstract
The power density spectrum of the received acoustic waveform after reflection off the time-varying random sea surface is evaluated at an arbitrary observation point in the farfield. For a monochromatic transmitted signal and a narrow-band Gaussian surface-height variation, the received acoustic spectrum is shown to consist of an impulse at the transmitted acoustic frequency plus sidelobes centered at frequencies separated from the transmitted frequency by multiples of the surface center frequency. The powers in the coherent component and scattered sideband components of the received pressure waveform are evaluated in terms of the surface roughness and spatial-temporal correlation function of the surface. For the special case of elliptical contours of iso- correlation at zero time delay, the sideband powers and scattering strengths are evaluated in terms of two fundamental parameters that include the geometry of the experiment, the incident acoustic frequency, the root mean square (rms) surface height, and the surface correlation distances. The rms bandwidths of the sideband scatter components are evaluated for small surface roughness and shown to be approximately proportional to the square root of the sideband number. Numerous examples of sideband scattering strengths for a variety of spatial correlation functions, including exponential and Gaussian decay as special cases, are given.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 25, 1970
- Accession Number
- AD0714482
Entities
People
- Albert H. Nuttall
- Benjamin F. Cron
Organizations
- Naval Underwater Systems Center