Drittes Physikalisches Inst., Univ. of Gottingen, Burger-str. 42--44, D-37073 Gottingen, Germany
The classification of submerged bodies with respect to internal properties (material, etc.), rather than geometrical shape, should be possible by means of their scattering resonances. This approach is known as the resonance scattering theory (RST). An essential extension of the RST theory with respect to solving practical problems is possible by applying to the acoustical scattering problem the so-called R-matrix theory (RMT), which has been developed by Wigner and Eisenbud to describe nuclear reactions. This theory includes in a natural way the linewidths, the coupling of the different resonant modes, and the overlapping of the resonances. Properly defined resonances provide the basis from which the whole formalism is constructed, while in the former theory the resonances are introduced after computing the scattering cross section. This allows an extension of the ``acoustical spectroscopy'' of isolated resonances as introduced by Brill to the practically important case of strongly overlapping resonances. However, isolated resonances are included in the RMT theory as special cases as well. A model function is proposed that can be matched---without knowledge of the scattering cross section---to measured differential cross sections in order to extract the resonance features.