An analytical solution is presented for the electromagnetic scattering from a dielectric circular cylinder embedded in a dielectric half-space with a slightly rough interface. The solution utilizes the spectral (plane-wave) representation of the fields and accounts for all the multiple interactions between the rough interface and the buried cylinder. First-order coefficients from the small perturbation method are used for computation of the scattered fields from the rough surface. The derivation includes both TM and TE polarizations and can be easily extended for other cylindrical buried objects (e.g., cylindrical shell, metallic cylinder). Several scattering scenarios are examined utilizing the new solution for a dielectric cylinder beneath a flat, sinusoidal, and arbitrary rough surface profile. Results indicate that the scattering pattern of a buried object below a slightly rough surface differs from the flat surface case only when the surface roughness spectrum contains a limited range of spatial frequencies. Furthermore, the illuminated area of the incident wave is seen to be a critical factor in the visibility of a buried object below a rough surface.

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Hydrographic data collected with a towed, depth‐cycling instrument (Batfish) in the frontal regions of warm‐core ring 82H during and immediately after its formation were analyzed to study small‐scale structure and processes. The frontal and slope water regions are characterized by a complex water‐mass structure resulting from mixing of the shelf, the slope, and the Sargasso Sea waters. Thermohaline intrusions along constant density surfaces are frequently observed. Two forms of thermohaline intrusions are studied in detail: subsurface tonguelike intrusions and cold filaments. A subsurface tongue of shelf water origin was found in the slope water region outside the frontal zone at 70‐m depth. It had a width of 4 km, a thickness of 20 m, and a length of at least 40 km, and moved in a southeast direction toward the front. Alongside the subsurface tongue, a cold filament 10 km wide, extending from the surface to 120‐m depth, was observed. As the subsurface tongue and the filament moved toward the frontal zone, their orientation became more and more aligned with the front. When they reached the front, the strong frontal current carried them downstream and hence prevented further intrusion into the ring. Mixing in the form of interleaving then became the most important process for cross‐front mixing. Interleaving occurs along the side walls of the subsurface tongue and filament, with more intense interleaving associated with stronger intrusions. This suggests a double‐diffusive generation mechanism of the interleaving.

Abstract-The idea of using acoustically induced Doppler spectra as a means for target detection and identification is introduced. An analytical solution for the calculation of the bistatic scattered Doppler spectrum from an acoustically excited, vibrating metallic circular cylinder is presented. First the electromagnetic scattering solution of a slightly deformed circular cylinder is obtained using a perturbation method. Then, assuming the vibration frequency is much smaller than the frequency of the incident electromagnetic wave, a closed form expression for the time-frequency response of the bistatic scattered field is obtained which can be used directly for estimating the Doppler spectrum. The acoustic scattering solution for an incident acoustic plane wave upon a solid elastic cylinder is applied to give the displacement of the cylinder surface as a function of time. Results indicate that the scattered Doppler frequencies correspond to the mechanical vibration frequencies of the cylinder, and the sidelobe Doppler spectrum level is, to the first order, linearly proportional to the degree of deformation and is a function of bistatic angle. Moreover, the deformation in the cylinder, and thus the Doppler sidelobe level, only becomes sizeable near frequencies of normal modes of free vibration in the cylinder. Utilizing the information in the scattered Doppler spectrum could provide an effective means of buried object identification, where acoustic waves are used to excite the mechanical resonances of a buried object.

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