MEASUREMENTS AND ANALYSIS OF ACOUSTIC BACKSCATTERING BY ELASTIC CUBESAND IRREGULAR POLYHEDRA

Underwater acoustic studies of backscattering by submerged targets hav e generally focused on bodies with spherical and cylindrical symmetry, However, there are interests in scattering by objects which may be ch aracterized by more angular features, with surfaces that tend to be co mposed of facets and edges, To investigate the scattering properties o f such bodies, the backscattering by a number of elastic cubes, and ir regularly shaped polyhedra, have been studied. Data were collected by measuring the band limited impulse response of the scatterers, using a broadband transducer, which operated as a transceiver, both transmitt ing and receiving signals. To present the scattering measurements nond imensionally a form function definition has been employed to normalize the backscattered signals. The normalized frequency has been expresse d as ka, where k is the acoustic wave number, and a is a characteristi c dimension of the scatterer. The cube observations covered a broad ka range, ka = 3-34, thereby encompassing the lower ka scattering region where the cube can be considered to be nominally rigid, through to hi gher ka values where it would be expected that the elastic properties of the cube become important. The measurements on irregular polyhedra are more limited in extent, however, the results are presented for com parison with the cube data. To compare the observations with predictio ns, computations of acoustic backscattering for both rigid and elastic cubes are presented. (C) 1997 Acoustical Society of America.