Determination of material composition from time-domain and frequency-domain resonance echoes of submerged elongated elastic targets
Abstract
When scattering from elastic targets backscattered echoes yield interesting information in the resonance region. In particular, resonance scattering theory in the frequency domain along with the circumferential nature of resonances imply that material constituency is a characteristic of resonance location. Moreover, recent discussions of resonance signatures in the time domain [see Uberall's book to be published on resonance scattering] can also yield information concerning resonance widths and average phase velocities which can also be related to material characteristics. By adjusting the orientation of the target over a suitable angular region it is possible to ascertain certain symmetries of the target if they exist, particularly if one varies the frequencies over a suitable range of resonances. If one observes axial symmetry through such a process, then it is possible to obtain both the dimensions of the object and the aspect ratio of the object (ratio of length to width). This is assuming that the target is in a “free” environment; that is, the boundaries of the target are not a factor in calculation. Time‐domain responses for specific pulse types also yield information and it is easy to see how a series of questions can form the basis of a scenario that can rule out certain targets or lead to a probability (confidence level) that specific targets are present. To determine the extent that this can be done, targets are examined which are composed of five materials for elastic solid spheroids for aspect ratios of 3 to 1 and 6 to 1 for end‐on incidence and for the case of 4 to 1 for all incident angles.
