Jerald W. Caruthers
Naval Res. Lab., Stennis Space Center, MS 39529
Jorge C. Novarini
PSI, Long Beach, MS 39560
In 1991 and again in 1993, the Acoustic Reverberation Special Research Program (ARSRP) of the Office of Naval Research conducted low-frequency acoustic reverberation experiments just west of the Mid-Atlantic Ridge. To support analyses of these measurements, the ARSRP also conducted geological and geophysical surveys of the region, resulting in nearly full-coverage bathymetry gridded to a resolution of 200x200 m. Direct-path reverberation data have been modeled successfully using Lambert's law applied to the local grazing angle determined from the high-resolution bathymetry. Excellent agreement of this simple model with data shows clearly that, for this region, knowledge of the 2-D seafloor morphology at the proper scale determines the ability to predict reverberation. For a model such as Lambert's law, which glosses over the details of seafloor microroughness or texture at the scale of the acoustic wavelength ((lambda) = 6 m), the bathymetry scale that is critical is shown to be an order of magnitude or two above the acoustic scale. Lambert coefficients for the region varied depending on sedimentation and local geomorphology. For this region, explaining the success of Lambert's law and its regional differences might serve as a goal of more detailed theoretical efforts into scattering at the microscale. [Work supported by ONR.]