Dept. of Phys., Univ. of Rhode Island, Kingston, RI 02881
Ocean and Atmospheric Phys. Div., Arlington, VA 22217
An examination is made of the application of the far-field Born approximation to the case of high-frequency acoustic scattering from a thermally produced buoyant plume using a multiple bistatic antiparallel scattering geometry. Initial results indicate the failure of the predictions made by the far-field Born approximation. Further theoretical development includes the higher-order terms (wavefront curvature) in the far-field expansion to fully describe the scattering process. The previously simple relationship, however, between the scattered pressure field and the Fourier transform of the scattering field becomes greatly complicated. The problem is reduced by considering uniform vertical advection of the scattering field and by taking time series measurements of the plume. The resulting prescription relates the complex acoustic data to the two-dimensional Fourier transform of the scattering field through a two-dimensional low-pass filter function which includes the effects of the wavefront curvature terms and the beam pattern. Data are presented for the case of scattering from an unstable plume. Results confirm the predictions made by theory.