Measurements and modeling of acoustic scattering from partially and completely buried spherical shells

Abstract

The use of low-frequency sonars (2-15 kHz) is explored to better exploit scattering features of buried targets that can contribute to their detection and classification. Compared to conventional mine countermeasure sonars, sound penetrates better into the sediment at these frequencies, and the excitation of structural waves in the targets is enhanced. The main contributions to target echo are the specular reflection, geometric diffraction effects, and the structural response, with the latter being particularly important for man-made elastic objects possessing particular symmetries such as bodies of revolution. The resonance response derives from elastic periodic phenomena such as surface circumferential waves revolving around the target. The GOATS'98 experiment, conducted jointly by SACLANTCEN and MIT off the island of Elba, involved controlled monostatic measurements of scattering by spherical shells which were partially and completely buried in sand, and suspended in the water column. The analysis mainly addresses a study of the effect of burial on the dynamics of backscattered elastic waves, which can be clearly identified in the target responses, and is based on the comparison of measurements with appropriate scattering models. Data interpretation results are in good agreement with theory. This positive result demonstrates the applicability of low-frequency methodologies based on resonance analysis to the classification of buried objects.

Modeling acoustic target response by component

“…Given these straightforward equations and appropriate boundary conditions (including perfectly matched layers (PMLs) [17] at the exterior of the modeled water to prevent reflection of the scattered wave), we produce an estimate of the scattered response which matches to a high degree of fidelity with the analytic solution [18] and with data collected in freefield tank experiments at NRL, including phenomena which are interpreted as specular response, resonant components, and surface-guided fluidborne waves. A cartoon representation of this full-physics model is shown in Figure 1a.…”

“…A similar technique was applied to cylindrical shells [10], and physical parameters of the shells were then estimated from the isolated resonances. This work was extended to include the study of buried shells [11]. Matching pursuits [12] have been used to decompose responses into components of the general type (chirps, wavefronts, decaying sinusoids) expected from scatterers.…”

Application of a minimum probability of error classifier with Linear Time-Varying pre-filters for buried target recognition

“…Figs. 3 and 4 give the burial states and the relative geometries used to derive theoretical target impulse responses based on the work in [5]- [9]. Also, the geometrical and the physical parameters of the spherical shell and the sediment are summarized in Tables I and II, respectively. Unfortunately, in many practical applications one cannot reasonably assume the interference component, w, of the Thus, one is faced with the challenge of balancing the demands of reality with a desire for optimality.…”

Numerical Analysis of the Backscattering Amplitude for a Partially Buried Cylinder on a Flat Interface Using Method of Moments

“…Although the investigation of the scattering of sound by partially buried object in sediment has been performed experimentally, [1] and theoretically, [2] the development of fast numerical methods could be helpful for giving insight into aspects of the scattering for a partially buried object.…”