By Sabrina Matteucci
Scattering from axially symmetric objects: theory, FEMLAB model implementation and results. NURC-FR-2006-010. April 2006.
The areas of operational relevance addressed by this report are proud and buried target detection and classification. Low frequency SONAR techniques, in the range below 50 kHz for typical mine like objects, have the potential of improving the detection and classification of buried and proud targets. The advantage associated with the low frequencies is that such signals can penetrate the outer shell of the illuminated target, and interact with its interior structure. Hence, low frequency echoes can be used to detect acoustically the presence of explosive inside a target, such as for example a mine or an improvised explosive device. The penetration of low frequency sound into the sediment makes it also possible to obtain echoes from completely buried targets. A fundamental disadvantage associated with the low frequencies is that the spatial resolution is too low to make imaging-like classification possible. For this reason, it is necessary to devise physics-based processing techniques, which can aid in the detection and classification of low frequency echoes. To develop such techniques, it is necessary to rely on a priori knowledge of the low frequency echo structure. Such knowledge can come from numerical simulations or from experimental data. On the other hand, particularly the initial phases of such a research require the availability of reliable target echo models, so that it becomes possible to conduct broadband studies for a variety of different targets, in an affordable amount of time. A numerically efficient modeling tool for the computation of echoes scattered by axially symmetric targets with internal structure is presented. This report presents the mathematical formulation on which the tool is based, implementation instructions, and verified numerical results.