Abstract:

Bottom loss was measured at a shallow-water (188m) site off the Gulf of Mexico using an L-shaped array. The L-shaped array consisted of a vertical component 153 m long covering most of the water column and a horizontal component 240 m long laid on the bottom. A source transmitting 10-s LFMs (40--440 Hz) continuously was towed toward, then away from the array. It was towed perpendicularly to the horizontal component of the array with a CPA (closest-point approach) about 250 m away from the center of the array. With the vertical component of the array, direct, surface reflected, bottom reflected, surface--bottom, bottom--surface, and surface--bottom--surface paths were identified. Bottom loss from single bottom bounce arrival over grazing angle from 10--40 deg were measured directly using the vertical component of the array. Because the horizontal component of the array was laid on the bottom, the ``(1+R) effect,'' the coherent sum of the arrival incident on the bottom and the resultant bottom reflection for that arrival, was measured. The (1+R) measurement was used to examine the geoacoustic bottom model of the site. [Work supported by the U.S. Navy.]