Fast Computation of Scattering from Elastic Targets

While the use of high frequency SAS imaging and subsequent use of pattern recognition techniques have proven to be useful in detection and classification of proud targets, these techniques by themselves cannot be applied when the targets are buried in the bottom, as high frequencies sonar signals are severely attenuated there. For this reason, the use of low-frequency techniques, which reveal target resonances and other structural features is sought, either as a stand-alone or a complimentary method. High fidelity models that can produce target response to sonar in a realistic ocean environment are important because they can be used to train classifiers to be able to perform automatic target recognition (ATR). They can also be used to simulate realistic minehunting scenarios. However, these tasks require not only accurate, but very fast models. In this work we use the finite element capabilities developed during Phase II of this effort to 1) develop very fast scattering models using the fast multipole method (FMM) and 2) further investigate the use of modulated radiation pressure to facilitate detection and classification of underwater mines and UXOs and determine ways that this technology can be used to enhance the performance of existing minehunting systems.