Broadband ultrasonic target strengths of hollow ceramic flotation spheres

The target strengths of hollow ceramic flotation spheres manufactured by DeepSea Power and Light, Inc., and tested to a pressure equivalent of 12,000 m have been measured as a function of frequency over the bands 10-150 kHz. The spheres are made of alumina, purity 99.9%, with diameter 91.44 ± 0.2 mm, nominal thickness 1.3 mm, mass 140 ± 1 g. The target strength spectra have also been calculated theoretically assuming a mass density of 3.984 g/cm³, longitudinal- and transverse-wave sound speeds of 11000 and 6510 m/s, respectively. Measurements and computations are compared. Potential applications of the sphere as a standard acoustic target are noted.