Acoustic Scattering from the Ocean Bottom

An experiment has been conducted to obtain the intensity field of sound scattered from a relatively rough region of the ocean bottom. Pulsed 19.5-kc/sec transmissions, directed towards the bottom, were made from a ship as it approached and passed a special radio sonobuoy. Sets of data were taken with the beam incident on the bottom at grazing angles between 30 and 90 degrees. Bottom-scatter returns in the monostatic direction were received on the source transducer, while reception in other directions was made by the buoy. The source was a tiltable piston transducer with a beam width of approximately 8°. The buoy hydrophone was omnidirectional in the horizontal plane with a rejection of surface-reflected signals in the vertical plane. The data were analyzed on the basis of an isotropic-scatter model, taking the velocity gradient into consideration. Results are presented in the form of polar plots of bottom scattering strength These intensity fields have been obtained from areas east of Bermuda for two bottom types, mudcoral and ooze, in water depths of approximately 750 and 1250 fathoms, respectively. Implications of the characteristics of these fields, along with results of other aspects of the data, are discussed in paper BB6.