ASA 125th Meeting Ottawa 1993 May

2aUW5. Broadband bottom scattering measurements in shallow and deep water.

Steven O. McConnell

John H. McCown

Arete Associates, P.O. Box 8050, La Jolla CA 92038

Measurements using broadband signals with bandwidths up to 5 kHz were made in shallow and deep water off San Diego. At the shallow (180--500 m) location 1- to 6-kHz coded signals were used for gathering simultaneous forward loss and backscattering data at grazing angles between 10(degrees) and 40(degrees). Time resolutions as small as 0.25 ms were achieved and from the forward loss measurements these high resolution data clearly revealed a medium scale (~10[sup 2] m) patchiness in the surficial sediment type alternating between sand and silt. The deep (1800-m) water measurements were taken at a deep sea drilling project site using a combination of 1- to 5-kHz coded pulses and 0.05- to 2 kHz-bandpassed SUS charges. Fine scale subbottom layering with typical thicknesses of 1--10 m down to 130 m were delineated using these broadband source signals. The coded pulses yielded a better definition of this layered structure in the upper 40 m, but were limited in depth of penetration because of increased attenuation at higher frequencies. [Work supported by ONR-AEAS.]