Experimental and modeling analysis of near-field scattering from complex targets

Abstract

Classification and detection of targets based on the analysis of structural resonances has been of prime interest to ocean acousticians for a long time. To further the understanding on scattering from complex targets, the EVA'06 experiment was conducted by a group of teams that included NURC, NRL and MIT, o the island of Elba in Italy. The experiment involved controlled monostatic and bistatic, near field and far field measurements of scattering from proud and half buried targets, which are representative of real world mines. This thesis focuses on the analysis of near-field bistatic data set obtained by supercritically insonifying proud composite targets and subcritically insonifying an empty spherical shell. Specifically, the arrival times of different waves known to be generated by scattering from cylindrical and spherical shells have been computed at different azimuths and vertical angles. These traces have been obtained by analyzing the experimental data and from simulations using OASES/SCATT. The arrival times, additionally, have been computed using geometry for the 'in-plane' i.e, precise forward and back scattering configurations. This enables accurate identification of different waves for these two azimuths which are then followed with the cage rotation. Also, the average intensity recorded at each receiver as a function of frequency and cage rotation is illustrated in the dome plots. Finally, in the experimental plots some unidentified arrivals have been noted, which could be the waves supported by the filler material contained inside. This work, thus, presents a comprehensive treatment of near-field scattering from complicated targets and provides a framework to do future work on deciphering the arrival times of more complicated waves from targets of arbitrary geometry.